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GitLab Flavored Markdown (GLFM) Specification Guide

Summary

  • GitLab Flavored Markdown (GLFM) is based on GitHub Flavored Markdown (GFM), which is based on CommonMark.
  • GLFM is divided into two "sets" of Markdown syntax:
    • An "official specification", which is not dependent upon any specific implementation or environment, and can be supported in any editor.
    • "Internal extensions", which may be dependent upon the GitLab environment and metadata.
  • Everything in each of these sets of syntax is specified by special Markdown files based on the CommonMark specification syntax, which contain side-by-side "examples" of Markdown and the corresponding generated HTML, and associated documentation describing each example.
  • There are also YAML metadata files, which may contain additional information on how individual Markdown/HTML examples should be processed and rendered.
  • These Markdown/YAML files and the examples they contain serve multiple goals:
    • They are the canonical "source of truth" for how GLFM should be rendered.
    • They support rendering a formatted HTML document containing all of the examples and associated documentation, as the GFM and CommonMark specs also do.
    • They support running standard CommonMark conformance testing against the official specification.
    • They support snapshot testing of GitLab internal GLFM processing logic. This is accomplished by automatically generating YAML "example snapshot files" which are used as fixtures to drive automated testing within the GitLab app.
  • There are various scripts and logic which are used to accomplish the above goals.

Introduction

GitLab supports Markdown in various places. The Markdown dialect we use is called GitLab Flavored Markdown (GLFM).

NOTE: In this document, GFM refers to GitHub Flavored Markdown, not GitLab Flavored Markdown. Refer to the section on acronyms for a detailed explanation of the various acronyms used in this document.

The specification for the GLFM dialect is based on the GitHub Flavored Markdown (GFM) specification, which is in turn based on the CommonMark specification. The GLFM specification includes many additions compared to the GFM specification.

This guide is a developer-facing document that describes the various terms and definitions, goals, tools, and implementations related to the GLFM specification. It is intended to support and augment the user-facing documentation for GitLab Flavored Markdown.

NOTE: This guide and the implementation and files described in it are still a work in progress. As the work progresses, rewrites and consolidation between this guide and the user-facing documentation for GitLab Flavored Markdown are likely.

Terms and definitions

Acronyms: GLFM, GHFM, GFM, CommonMark

GitHub Flavored Markdown is widely referred to by the acronym GFM, and this document follows that convention as well. GitLab Flavored Markdown is referred to as GLFM in this document, to distinguish it from GitHub Flavored Markdown.

Unfortunately, this convention is not yet followed consistently in the rest of the documentation or GitLab codebase. In many places, the GFM acronym is used to refer to GitLab Flavored Markdown. An open issue exists to resolve this inconsistency.

Some places in the code refer to both the GitLab and GitHub specifications simultaneous in the same areas of logic. In these situations, GitHub Flavored Markdown may be referred to with variable or constant names like ghfm_ to avoid confusion. For example, we use the ghfm acronym for the ghfm_spec_v_0.29.md GitHub Flavored Markdown specification file, which is committed to the gitlab repository and used as input to the update_specification.rb script.

The original CommonMark specification is referred to as CommonMark (no acronym).

Various Markdown specifications

The specification format we use is based on the approach used in CommonMark, where a spec.txt file serves as documentation, as well as being in a format that can serve as input to automated conformance tests. It is explained in the CommonMark specification:

This document attempts to specify Markdown syntax unambiguously. It contains many examples with side-by-side Markdown and HTML. These examples are intended to double as conformance tests.

Here are the HTML-rendered versions of the specifications:

However, GLFM has more complex parsing, rendering, and testing requirements than GFM or CommonMark. Therefore, it does not have a static, hardcoded, manually updated spec.txt. Instead, the GLFM spec.txt is automatically generated based on other input files. This process is explained in detail in the Implementation sections below.

NOTE: As of December 2022, the HTML version of the GitHub Flavored Markdown (GFM) specification is outdated, and does not match the specification's spec.txt. An issue has been filed in the cmark-gfm project to report this.

Official specifications vs internal extensions

GFM for GitHub and GLFM for GitLab have two "sets" of Markdown they support:

  • Official specification
  • Internal extensions

The following taxonomy chart shows the taxonomy and terminology of the various specifications:

graph TD
CM[CommonMark - spec.txt - for example, headings] --- GFMS[GFM Specification - spec.txt - for example, strikethrough extension]
GFMS --- GLFM[GLFM Specification - for example, color chips]
GFMS --- GFMI[GFM internal extensions - for example, GitHub-specific references]
GLFM --- GLFS[GLFM internal extensions - for example, GitLab-specific references]
Official specifications

GFM and GLFM each have an official specification, which includes both:

  1. The CommonMark standard.
  2. Generic extensions to the CommonMark standard.

For example, GFM adds the strikethrough extension, and GLFM adds the color chips extension. These extensions in the official specifications are not dependent upon any specific implementation or environment. They can be implemented in any third-party Markdown rendering engine.

Internal extensions

GFM and GLFM each also have a set of internal extensions. These extensions are not part of the GFM or GLFM official specifications, but are part of the GitHub and GitLab internal Markdown renderer and parser implementations. These internal extensions are often dependent upon the GitHub or GitLab implementations or environments, and may depend upon metadata which is only available via interacting with those environments. For example, GitHub supports GitHub-specific automatically linked references, and GitLab also supports GitLab-specific references. These may also be implemented by third-party Markdown rendering engines which integrate with GitHub or GitLab. For example, editor or IDE plugins which enable the user to directly edit Markdown for issues, pull requests, or merge requests within the editor or IDE.

Markdown examples

Everywhere in the context of the specification and this guide, the term examples is specifically used to refer to the convention of using backtick-delimited Markdown + HTML pairs to illustrate the canonical parsing (or rendering) behavior of various Markdown source strings in the standard CommonMark specification format.

In this context, it should not be confused with other similar or related meanings of example, such as RSpec examples.

See the section on the glfm_official_specification.md file for more details on the backtick-delimited Markdown+HTML example syntax.

Parsers and renderers

To understand the various ways in which a specification is used, and how it related to a given Markdown dialect, it's important to understand the distinction between a parser and a renderer:

  • A Markdown parser accepts Markdown as input and produces a Markdown Abstract Syntax Tree (AST) as output.
  • A Markdown renderer accepts the AST produced by a parser, and produces HTML (or a PDF, or any other relevant rendering format) as output.

Types of Markdown tests driven by the GLFM specification

The two main types of automated testing are driven by the Markdown examples and data contained in the GLFM specification. We refer to them as:

  • Markdown conformance testing.
  • Markdown snapshot testing.

Many other types of tests also occur in the GitLab codebase, and some of these tests are also related to the GLFM Markdown dialect. Therefore, to avoid confusion, we use these standard terms for the two types of specification-driven testing referred to in this documentation and elsewhere.

Markdown conformance testing

NOTE: Markdown conformance testing for GLFM is not yet implemented.

Markdown conformance testing refers to the standard testing method used by all CommonMark Markdown dialects to verify that a specific implementation conforms to the CommonMark Markdown specification. It is enforced by running the standard CommonMark tool spec_tests.py against a given spec.txt specification and the implementation, as described in the specification itself

Conformance testing is only to be run against GLFM official specification examples, and is not to be run against internal extension examples. This is because the internal extension examples may have dependencies on the GitLab environment or metadata, but the standard CommonMark conformance testing tool does not support this.

NOTE: spec_tests.py may eventually be re-implemented in Ruby, to not have a dependency on Python.

Markdown snapshot testing

Markdown snapshot testing refers to the automated testing performed in the GitLab codebase, which is driven by example_snapshots fixture data derived from all of the examples in the GLFM specification. It consists of both backend RSpec tests and frontend Jest tests which use the fixture data. This fixture data is contained in YAML files. These files are generated and updated based on the Markdown examples in the specification, and the existing GLFM parser and render implementations. They may also be manually updated as necessary to test-drive incomplete implementations.

Snapshot testing is intended to be comprehensive, so it is run against all examples - both the GLFM official specification and internal extension examples. This means that it uses configuration files to support providing GitLab-specific environment or metadata which is required by internal extension examples, such as glfm_example_metadata.yml.

The design of the snapshot testing helps ensure the correctness of the user-facing GLFM Markdown. The testing thoroughly exercises the backend and frontend parsers and renderers by using a black-box testing approach. It can be considered a type of high-level testing at the "top of the testing pyramid" because of this comprehensive style.

Regarding the terminology used for Markdown snapshot testing:

  1. The Markdown snapshot tests can be considered a form of the Golden Master Testing approach, which is also referred to as Approval Testing or Characterization Testing.
    1. The term Golden Master originally comes from the recording industry, and refers to the process of mastering, or making a final mix from which all other copies are produced.
    2. For more information and background, you can read about Characterization Tests and Golden Masters.
  2. The usage of the term snapshot does not refer to the approach of Jest snapshot testing, as used elsewhere in the GitLab frontend testing suite. However, the Markdown snapshot testing does follow the same philosophy and patterns as Jest snapshot testing:
    1. Snapshot example fixture data is represented as files which are checked into source control.
    2. The files can be automatically generated and updated based on the implementation of the code under tests.
    3. The files can also be manually updated when necessary, for example, to test-drive changes to an incomplete or buggy implementation.
  3. The usage of the term fixture does not refer to standard Rails database fixture files. It instead refers to test fixtures in the more generic definition, as input data to support automated testing.
  4. These example snapshots fixture files are generated from and closely related to the rest of the GLFM specification. Therefore, the example_snapshots directory is colocated under the glfm_specification directory with the rest of the GLFM specification files. They are intentionally not located under the spec/fixtures directory with the rest of the fixture data for the GitLab Rails application. In practice, developers have found it simpler and more understandable to have everything under the glfm_specification directory rather than splitting these files into the spec/fixtures directory.

See also the section on normalization below, which is an important concept used in the Markdown snapshot testing.

Parsing and Rendering

The Markdown dialect used in the GitLab application has a dual requirement for rendering:

  1. Rendering to static read-only HTML format, to be displayed in various places throughout the application.
  2. Rendering editable content in the rich text editor, a "What You See Is What You Get" (WYSIWYG) editor. The rich text editor supports real-time instant switching between an editable Markdown source and an editable WYSIWYG document.

These requirements means that GitLab has two independent parser and renderer implementations:

  1. The backend parser / renderer supports parsing and rendering to static read-only HTML. It is implemented in Ruby. It leverages the commonmarker gem, which is a Ruby wrapper for libcmark-gfm, GitHub's fork of the reference parser for CommonMark. libcmark-gfm is an extended version of the C reference implementation of CommonMark
  2. The frontend parser / renderer supports parsing and WYSIWYG rendering for the rich text editor. It is implemented in JavaScript. Parsing is based on the Remark Markdown parser, which produces a MDAST Abstract Syntax Tree (MDAST). Rendering is the process of turning an MDAST into a ProseMirror document. Then, ProseMirror is used to render a ProseMirror document to WYSIWYG HTML. In this document, we refer to the process of turning Markdown into an MDAST as the frontend / JavaScript parser, and the entire process of rendering Markdown to WYSIWYG HTML in ProseMirror as the rich text editor. Several requirements drive the need for an independent frontend parser / renderer implementation, including:
    1. Lack of necessary support for accurate source mapping in the HTML renderer implementation used on the backend.
    2. Latency and bandwidth concerns: eliminating the need for a round-trip to the backend every time the user switches between the Markdown source and the WYSIWYG document.
    3. Different HTML and browser rendering requirements for WYSIWYG documents. For example, displaying read-only elements such as diagrams and references in an editable form.

Multiple versions of rendered HTML

Both of these GLFM renderer implementations (static and WYSIWYG) produce HTML which may differ from the canonical HTML examples in the GLFM official specification. Therefore, for every Markdown example in the GLFM specification, three versions of HTML can potentially be rendered from the example:

  • Static HTML
  • WYSIWYG HTML
  • Canonical HTML

Static HTML

Static HTML is HTML produced by the backend (Ruby) renderer, which contains extra styling and behavioral HTML. For example, Create task buttons added for dynamically creating an issue from a task list item. The GitLab Markdown API generates HTML for a given Markdown string using this method.

The Markdown specified in the Markdown examples is used to automatically generate HTML in glfm_specification/output_example_snapshots/html.yml via update-example-snapshots.rb. These examples are used when running Markdown snapshot testing.

WYSIWYG HTML

WYSIWYG HTML is HTML produced by the frontend (JavaScript) rich text editor, which includes parsing and rendering logic. It is used to present an editable document in the ProseMirror WYSIWYG editor.

Just like static HTML, the Markdown specified in the Markdown examples is used to automatically generate HTML in glfm_specification/output_example_snapshots/html.yml via update-example-snapshots.rb. These examples are used when running Markdown snapshot testing.

Canonical HTML

Canonical HTML is the clean, basic version of HTML rendered from Markdown, with no unnecessary classes/elements related to styling or any other implementation-specific behavior.

Its purpose is to support Markdown conformance testing against the GLFM spec.txt.

Always hardcoded and manually curated, the HTML is never automatically generated. The Markdown examples specifying it are contained in different files depending on which Markdown specification a given example originally comes from.

Canonical HTML is always specified for all Markdown examples in the CommonMark, GFM, and GLFM official specifications.

However, it is never specified for GLFM internal extensions in the Markdown examples. This is because the internal extensions are never tested via Markdown conformance testing. Therefore, canonical HTML for internal extension examples is never used by any scripts or automated testing.

Here are more details on the sources of canonical HTML examples:

  1. For the examples which are part of the CommonMark specification and GFM extensions specification, the canonical HTML is the exact identical HTML found in the GFM spec.txt Markdown example blocks. These examples are copied verbatim from the GFM spec.txt into the GLFM version of spec.txt.
  2. For the examples which are part of the GLFM official specification, the canonical HTML is manually maintained and curated via the examples contained in the glfm_official_specification.md input specification file.
  3. For the examples which are part of the GLFM internal extensions, the canonical HTML is never specified, and must be left empty in all examples contained in the glfm_internal_extensions.md input specification file.

Canonicalization of HTML

The rendered static HTML and WYSIWYG HTML from the backend (Ruby) and frontend (JavaScript) renderers usually contains extra styling or HTML elements, to support specific appearance and behavioral requirements.

Neither the backend nor the frontend rendering logic can directly render the clean, basic HTML which is necessary to perform comparison to the canonical HTML when running Markdown conformance testing for the GLFM official specification examples.

Nor should they be able to, because:

  • It's not a direct requirement to support any GitLab application feature.
  • Adding this feature adds unnecessary requirements and complexity to the implementations.

Instead, the rendered static or WYSIWYG HTML is converted to canonical HTML by a canonicalization process. This process can strip all the extra styling and behavioral HTML from the static or WYSIWYG HTML, resulting in canonical HTML which exactly matches the canonical HTML examples in a standard spec.txt specification.

Use the canonicalize-html.rb script for this process.

Normalization

Versions of the rendered HTML and ProseMirror JSON can vary for a number of reasons. Differences in styling or HTML structure can occur, but the values of attributes or nodes may also vary across different test runs or environments. For example:

  1. Database record identifiers
  2. Namespace or project identifiers
  3. Portions of URIs
  4. File paths or names
  5. Random values

For the Markdown snapshot testing to work properly, you must account for these differences in a way that ensures the tests are reliable, and always behave the same across different test runs or environments.

To account for these differences, there is a process called normalization. Several ways to approach normalization exist:

  1. Fixture-based normalization
  2. Environment-variable-based normalization
  3. Regex-based normalization

Fixture-based normalization

Fixture-based normalization should be used whenever possible, because it is simpler and easier to understand than regex-based normalization.

The Markdown snapshot testing uses RSpec to generate the example snapshot files. RSpec enables you to:

  • Use the same powerful fixture support and helpers as all the rest of the GitLab RSpec suite.
  • Use fixtures to control the state of the database when the example snapshots are generated.
  • Extract this fixture setup to an RSpec shared context. This shared context is used to ensure the same database state exists wherever the snapshot tests are run, either by the CI suite, or locally via run-snapshot-tests.sh.

You can see the RSpec shared context containing these fixtures in spec/support/shared_contexts/glfm/example_snapshot_fixtures.rb.

Environment-variable-based normalization

In some cases, fixtures may not be usable, because they do not provide control over the varying values. In these cases, we can introduce support for a environment variable into the production code, which allows us to override the randomness in our test environment when we are generating the HTML for footnote examples. Even though it is in the production code path, it has no effect unless it is explicitly set, therefore it is innocuous. It allows us to avoid the more-complex regex-based normalization described below.

The current example of this is when footnote IDs that are usually random are overridden to be deterministic by setting GITLAB_TEST_FOOTNOTE_ID. It is set along with the fixtures setup in the spec/support/shared_contexts/glfm/example_snapshot_fixtures.rb shared context.

Regex-based normalization

If neither fixture-based nor environment-variable-based normalization can be used, use regex-based normalization. It is powerful, but more complex, and requires more maintenance. It requires referring to specific examples by name, and crafting the proper regexes.

Regex-based normalization allows custom regular expressions with capturing groups to be applied to two different versions of HTML or JSON for a given Markdown example, and the contents of the captured groups can be replaced with the same fixed values.

Then, the two normalized versions can be compared to each other to ensure all other non-variable content is identical.

NOTE: We don't care about verifying specific attribute values here, so it's OK if the normalizations discard and replace these variable values with fixed values. Different testing levels have different purposes:

  1. Markdown snapshot testing is intended to enforce the structure of the rendered HTML/JSON, and to ensure that it conforms to the canonical specification.
  2. Individual unit tests of the implementation for a specific Markdown example are responsible for specific and targeted testing of these variable values.

We also use this same regex capture-and-replace normalization approach for canonicalization of HTML, because it is essentially the same process. With canonicalization, instead of just replacing variable values, we are removing non-canonical portions of the HTML.

Refer to glfm_example_normalizations.yml for a detailed explanation of how the normalizations are specified.

Goals

Given all the constraints above, we can summarize the various goals related to the GLFM specification and testing infrastructure:

  1. There is an official specification and single source of truth for how GLFM should render Markdown to HTML. This source of truth is represented by three Markdown files:

    1. ghfm_spec_v_?.??.md for the CommonMark + GFM examples.
    2. glfm_official_specification.md for the GLFM official examples.
    3. glfm_internal_extensions.md for the GLFM internal extensions.

  2. This official specification meets these requirements:

    1. The specification is a strict superset of the GitHub Flavored Markdown (GFM) specification, just as GFM is a strict superset of the CommonMark specification.
    2. Therefore, it contains the superset of all Markdown examples for CommonMark and GFM, as well as the GLFM official specification and internal extensions.
    3. It contains sections and examples for all the additional Markdown contained in the GLFM official specification and internal extensions, with Markdown examples and any accompanying prose, just like the CommonMark and GFM examples.
    4. All headers and Markdown examples should be in the standard format, which can be processed by the standard CommonMark tool spec_tests.py used to perform Markdown conformance testing against all examples contained in a spec.txt.

  3. The GLFM parsers and HTML renderers for both the static backend (Ruby) and WYSIWYG frontend (JavaScript) implementations support consistent rendering of all canonical Markdown + HTML examples in the specification, as verified by run-spec-tests.sh.

    NOTE: Consistent does not mean that both of these implementations render to the identical HTML. They each have different implementation-specific additions to the HTML they render, so their rendered HTML is "canonicalized" to canonical HTML prior to running Markdown conformance testing.

  4. For both the static backend (Ruby) and WYSIWYG frontend (JavaScript) implementations, a set of example snapshots exists in the form of YAML files, which correspond to every Markdown example in the GLFM spec.txt. These example snapshots support the following usages for every GLFM Markdown example:

    1. The backend (Ruby) parser and renderer can convert Markdown to the expected custom static HTML.
    2. The frontend (JavaScript) parser and renderer (which includes GitLab custom code and Remark) can convert Markdown to the expected ProseMirror JSON representing a ProseMirror document.
    3. The rich text editor (which includes the frontend (JavaScript) parser and renderer, and ProseMirror) can convert Markdown to the expected custom WYSIWYG HTML as rendered by ProseMirror.
    4. The rich text editor can complete a round-trip test, which involves converting from Markdown, to MDAST, to ProseMirror Document, then back to Markdown. It ensures the resulting Markdown is exactly identical, with no differences.

Implementation

The following set of scripts and files is complex. However, it allows us to meet all of the goals listed above, and is carefully designed to meet the following implementation goals:

  1. Minimize the amount of manual editing, curation, and maintenance of the GLFM specification and related files.
  2. Automate and simplify the process of updating the GLFM specification and related files when there are changes to the upstream CommonMark spec, GFM extensions, or the GLFM extensions.
  3. Support partial or incomplete implementations of the GLFM specification, whether due to in-progress work, bugs, or new future Markdown support, while still performing all functionality for the existing implementations.
  4. Automate, simplify, and support running various tests, including the standard CommonMark conformance tests and GLFM-implementation-specific unit/acceptance Markdown snapshot tests.
  5. Provide a rich set of extensible metadata around all GLFM specification examples to support current and future requirements, such as automated acceptance testing and automated documentation updates.

The documentation on the implementation is split into three sections:

  1. Scripts.
  2. Specification files.
  3. Example snapshot files: These YAML files are used as input data or fixtures to drive the various tests, and are located under glfm_specification/output_example_snapshots. All example snapshot files are automatically generated based on the specification files and the implementation of the parsers and renderers. However, they can also be directly edited if necessary, such as to test-drive an incomplete implementation.

Scripts

These executable scripts perform various tasks related to maintaining the specification and running tests. Each script has a shell-executable entry point file located under scripts/glfm, but the actual implementation is in unit-tested classes under scripts/lib/glfm.

NOTE: Some of these scripts are implemented in Ruby, and others are shell scripts. Ruby scripts are used for more complex custom scripts, to enable easier unit testing and debugging. Shell scripts are used for simpler scripts which primarily invoke other shell commands, to avoid the challenges related to running other shell sub-processes from Ruby scripts.

NOTE: The Ruby executable scripts under scripts/glfm have dashes instead of underscores in the filenames. This naming is non-standard for a Ruby file, but is used to distinguish them from the corresponding implementation class entry point files under scripts/lib/glfm when searching by filename.

update-specification.rb script

The scripts/glfm/update-specification.rb script uses input specification files to generate and update Markdown and HTML output files for the spec.txt and spec.html output specification files as well as the snapshot_spec.md and snapshot_spec.html output example snapshot files.

The HTML files are created by passing the generated (or updated) Markdown to the backend API for rendering to HTML.

graph LR
subgraph script:
  S{update-specification.rb}
end
subgraph input - markdown files
  I1[glfm_official_specification.md - GLFM official specification examples] --> S
end
subgraph output - specification files
  S --> O1[spec.txt - GLFM official specification examples]
  S --> O2[spec.html - GLFM official specification examples]
end
graph LR
subgraph script:
  S{update-specification.rb}
end
subgraph input - markdown files
  I1[ghfm_spec_v_0.29.md - CommonMark and GHFM specification examples] --> S
  I2[glfm_internal_extensions.md - GLFM internal extension examples] --> S
end
subgraph output - example snapshot files
  S --> O1[snapshot_spec.md - CommonMark, GHFM, GLFM internal extension examples]
  S --> O2[snapshot_spec.html - CommonMark, GHFM, GLFM internal extension examples]
end

canonicalize-html.rb script

The scripts/glfm/canonicalize-html.rb handles the "canonicalization" of HTML. It is a pipe-through helper script which takes as input a static or WYSIWYG HTML string containing extra HTML, and outputs a canonical HTML string.

It is implemented as a standalone, modular, single-purpose script, based on the Unix philosophy. It's easy to use when running the standard CommonMark spec_tests.py script, which expects canonical HTML, against the GitLab renderer implementations.

run-spec-tests.sh script

scripts/glfm/run-spec-tests.sh is a convenience shell script which runs conformance specs via the CommonMark standard spec_tests.py script, which uses the ghfm_spec_v_0.29.md and glfm_specification/output_spec/spec.txt files with the scripts/glfm/canonicalize-html.rb helper script to test the GLFM renderer implementations' support for rendering Markdown specification examples to canonical HTML.

graph LR
subgraph scripts:
  A{run-spec-tests.sh} --> C
  subgraph specification testing process
    B[canonicalize-html.sh] --> C
    C[spec_tests.py]
  end
end
subgraph input
  D1[ghfm_spec_v_0.29.md GLFM specification] --> C
  D2[spec.txt GLFM specification] --> C
  E((GLFM static<br/>renderer implementation)) --> B
  F((GLFM WYSIWYG<br/>renderer implementation)) --> B
end
subgraph output:<br/>test results/output
  C --> G[spec_tests.py output]
end

update-example-snapshots.rb script

The scripts/glfm/update-example-snapshots.rb script creates and updates the example snapshot YAML files.

Its inputs are:

  • The glfm_specification/output_spec/snapshot_spec.md file, which contains the superset of all CommonMark, GFM, and GLFM official and internal examples.
  • The glfm_specification/input/gitlab_flavored_markdown/glfm_example_*.yml YAML files, which contain metadata to control how to generate the example snapshot files.
graph LR
subgraph script:
  A{update-example-snapshots.rb}
end
subgraph input: markdown input specification files
  B1[snapshot_spec.md] --> A
  C1[glfm_example_status.yml] --> A
  C2[glfm_example_normalizations.yml] --> A
  C3[glfm_example_metadata.yml] --> A
end
subgraph output: YAML example snapshot files
  A --> E[examples_index.yml]
  A --> F[markdown.yml]
  A --> G[html.yml]
  A --> H[prosemirror_json.yml]
end

run-snapshot-tests.sh script

The scripts/glfm/run-snapshot-tests.sh convenience shell script runs all relevant Markdown snapshot testing RSpec and Jest *_spec files (from main app spec folder) which are driven by example_snapshot YAML files.

The actual RSpec and Jest test *_spec files (frontend and backend) live under the usual relevant locations under spec, matching the location of their corresponding implementations. They can be run either:

  • As part of the standard pipelines.
  • From the command line or an IDE, just like any other file under spec.

However, they are spread across four different locations:

  • Backend tests under spec/requests.
  • Backend EE tests under ee/spec/requests.
  • Frontend tests under spec/frontend.
  • Frontend EE tests under ee/spec/frontend.

Therefore, this convenience script is intended to only be used in local development. It simplifies running all tests at once and returning a single return code. It contains only shell scripting commands for the relevant bundle exec rspec ... and yarn jest ... commands.

graph LR
subgraph tests:
  B[relevant rspec+jest test files]
end
subgraph script:
  A{run-snapshopt-tests.sh} -->|invokes| B
end
subgraph output:<br/>test results/output
  B --> H[rspec+jest output]
end
subgraph input:<br/>YAML
  C[examples_index.yml] --> B
  D[markdown.yml] --> B
  E[html.yml] --> B
  F[prosemirror_json.yml] --> B
end

verify-all-generated-files-are-up-to-date.rb script

The scripts/glfm/verify-all-generated-files-are-up-to-date.rb script runs the update-specification.rb. update-example-snapshots.rb scripts, It fails with an exception and non-zero return code if running these scripts results in any diffs to the generated and committed output specification files or example snapshot files.

This script is run via the glfm-verify CI job to ensure that all changes to the input specification files are reflected in the generated output specification and example snapshot files.

Specification files

These files represent the GLFM specification itself. They are all located under the root glfm_specification and are further divided into subcategories based on their usage and purpose:

Input specification files

Input specification files are manually curated Markdown files that represent the specification itself. They are located at glfm_specification/input/github_flavored_markdown/*.md and glfm_specification/input/gitlab_flavored_markdown/*.md.

See the main specification files section for more context and details.

GitHub Flavored Markdown specification

glfm_specification/input/github_flavored_markdown/ghfm_spec_v_0.29.md is a copy of the official latest GFM spec.txt.

  • It is automatically downloaded and updated by the update-specification.rb script.
  • When it is downloaded, the version number is added to the filename.
  • The extension is changed from *.txt to *.md so that it can be handled better by Markdown editors.

It currently contains additional Introduction and Appendix prose-only header sections which do not contain any examples.

All header sections which contain examples are expected to be contained within a contiguous file section which is delimited by:

  1. The beginning of the second H1 header (the first one after the Introduction section)
  2. An <!-- END TESTS --> HTML comment line.

NOTE: For extra clarity, this file uses the ghfm acronym in its name instead of gfm, as explained in the Acronyms section.

glfm_official_specification.md

glfm_specification/input/gitlab_flavored_markdown/glfm_official_specification.md consists of the manually updated Markdown+HTML examples for the GLFM official specification, and their associated documentation and descriptions.

  • It contains Markdown examples in the standard backtick-delimited spec.txt format, each of which contains Markdown and the corresponding canonical HTML that should be rendered.
  • For all GitLab examples, the "extension" annotation after the backticks should consist of only example. It does not currently include any additional extension annotations describing the specific Markdown, unlike the GitHub Flavored Markdown examples, which do include these additional annotations (such as example strikethrough).
  • The update-specification.rb script inserts it as new sections before the appendix of generated spec.txt.
  • It should consist of H1 header sections, with all examples nested either 2 or 3 levels deep within H2 or H3 header sections.
  • H3 header sections must be nested within H2 header sections. They cannot be nested directly within H1 header sections.

It may contain additional prose-only header sections which do not contain any examples.

All header sections which contain examples must be contained within a contiguous file section which is delimited by <!-- BEGIN TESTS --> and <!-- END TESTS --> HTML comment lines.

glfm_specification/input/gitlab_flavored_markdown/glfm_official_specification.md sample entries:

# Section with GLFM official specification examples

## Strong

### Strong with two asterisks

```````````````````````````````` example
**bold**
.
<p><strong>bold</strong></p>
````````````````````````````````

### Strong with HTML

```````````````````````````````` example
<strong>
bold
</strong>
.
<p><strong>
bold
</strong></p>
````````````````````````````````
glfm_internal_extensions.md

glfm_specification/input/gitlab_flavored_markdown/glfm_internal_extensions.md consists of the manually updated Markdown examples for the GLFM internal extensions, and their associated documentation and descriptions.

Its general format is identical to glfm_official_specification.md, consisting of H1, H2, or H3 sections containing Markdown examples in the standard backtick-delimited spec.txt format.

However, as described in the canonical HTML section, only the Markdown portion of each example is specified, and the HTML portion is left empty, because internal extension examples are never used for Markdown conformance testing.

It may contain additional prose-only header sections which do not contain any examples.

All header sections which contain examples must be contained within a contiguous file section which is delimited by <!-- BEGIN TESTS --> and <!-- END TESTS --> HTML comment lines.

glfm_specification/input/gitlab_flavored_markdown/glfm_official_specification.md sample entries:

NOTE: All lines in this example are prefixed with a | character. This prefix helps avoid false errors when this file is checked by markdownlint, and possible errors in other Markdown editors. The actual file should not have these prefixed | characters.

|# Section with GLFM Internal Extension Examples
|
|## Video
|
|```````````````````````````````` example
|![video](video.m4v "video title")
|.
|````````````````````````````````

Input specification configuration files

Input specification configuration files are manually curated YAML files that control various aspects of the automated GLFM scripts and processes. They are located at glfm_specification/input/gitlab_flavored_markdown/*.yml.

See the main specification files section for more context and details.

Configuration file validation

All of the manually curated example names in the configuration files must correspond to an existing Markdown example name found in output_example_snapshots/examples_index.yml, which is automatically generated based on the input specification files.

If there is an invalid reference to an example name that does not exist, the scripts/glfm/update-example-snapshots.rb script fails with a descriptive error.

The only exceptions to this validation are example names beginning with 00_, which are reserved for YAML aliases. See the section on glfm_example_normalizations.yml for more details and examples.

glfm_example_status.yml

glfm_specification/input/gitlab_flavored_markdown/glfm_example_status.yml controls the behavior of the scripts and tests.

  • It is manually updated.
  • The skip_update_example_snapshot* fields control the status of automatic generation of snapshot example entries based on Markdown examples.
  • The skip_running_* control allow Markdown conformance tests or Markdown snapshot tests to be skipped for individual examples.
  • This allows control over skipping this processing or testing of various examples when they are unimplemented, partially implemented, broken, cannot be generated, or cannot be tested for some reason.
  • All entries default to false. They can be set to true by specifying a Ruby value which evaluates as truthy. This could be the boolean true value, but ideally should be a string describing why the example's updating or testing is being skipped.
  • When a skip_update_example_snapshot* entry is true, the existing value is preserved. However, since the YAML is re-written, the style of the string value and its Block Chomping Indicator (|) may be modified, because the Ruby psych YAML library automatically determines this.

The following optional entries are supported for each example. They all default to false:

glfm_specification/input/gitlab_flavored_markdown/glfm_example_status.yml sample entry:

07_99_00_an_example_with_incomplete_wysiwyg_implementation_1:
  skip_update_example_snapshots: 'An explanation of the reason for skipping.'
  skip_update_example_snapshot_html_static: 'An explanation of the reason for skipping.'
  skip_update_example_snapshot_html_wysiwyg: 'An explanation of the reason for skipping.'
  skip_update_example_snapshot_prosemirror_json: 'An explanation of the reason for skipping.'
  skip_running_conformance_static_tests: 'An explanation of the reason for skipping.'
  skip_running_conformance_wysiwyg_tests: 'An explanation of the reason for skipping.'
  skip_running_snapshot_static_html_tests: 'An explanation of the reason for skipping.'
  skip_running_snapshot_wysiwyg_html_tests: 'An explanation of the reason for skipping.'
  skip_running_snapshot_prosemirror_json_tests: 'An explanation of the reason for skipping.'
glfm_example_normalizations.yml

glfm_specification/input/gitlab_flavored_markdown/glfm_example_normalizations.yml is used to control the fixture-based normalization process. It allows one or more regex/replacement pairs to be specified for a Markdown example.

  • It is manually updated.
  • It has a nested structure corresponding to the example and type of entry it refers to.
  • It extensively uses YAML anchors and aliases to avoid duplication of regex/replacement pairs and allow them to be shared across multiple examples.
  • The YAML anchors use a naming convention based on the index number of the example, to ensure unique anchor names and avoid naming conflicts.

NOTE: Other approaches to normalization such as fixture-based normalization or environment-variable-based normalization are always preferable to fixture-based normalization.

glfm_specification/input/gitlab_flavored_markdown/glfm_example_normalizations.yml sample entries:

# NOTE: All YAML anchors which are shared across one or more examples are defined in the `00_shared` section.
00_shared:
  00_uri: &00_uri
    - regex: '(href|data-src)(=")(.*?)(test-file\.(png|zip)")'
      replacement: '\1\2URI_PREFIX\4'
01_01_00__section_one__example_containing_a_uri__001:
  html:
    static:
      canonical:
        01_01_00_uri: *00_uri
      snapshot:
        01_01_00_uri: *00_uri
      wysiwyg:
        01_01_00_uri: *00_uri
  prosemirror_json:
    01_01_00_uri: *00_uri
07_01_00__gitlab_specific_markdown__footnotes__001:
  # YAML anchors which are only shared within a single example should be defined within the example
  shared:
    07_01_00_href: &07_01_00_href
      - regex: '(href)(=")(.+?)(")'
        replacement: '\1\2REF\4'
    07_01_00_id: &07_01_00_id
      - regex: '(id)(=")(.+?)(")'
        replacement: '\1\2ID\4'
  html:
    static:
      canonical:
        07_01_00_href: *07_01_00_href
        07_01_00_id: *07_01_00_id
      snapshot:
        07_01_00_href: *07_01_00_href
        07_01_00_id: *07_01_00_id
      wysiwyg:
        07_01_00_href: *07_01_00_href
        07_01_00_id: *07_01_00_id
  prosemirror_json:
    07_01_00_href: *07_01_00_href
    07_01_00_id: *07_01_00_id
glfm_example_metadata.yml

glfm_specification/input/gitlab_flavored_markdown/glfm_example_metadata.yml allows control over other aspects of the snapshot example generation process.

  • It is manually updated.
  • The ee fields determine whether the example is an EE-only example. If the ee field is true, the example will only be run by ee/spec/requests/api/markdown_snapshot_spec.rb, not by spec/requests/api/markdown_snapshot_spec.rb.
  • The api_request_override_path field overrides the API endpoint path which is used to generate the static HTML for the specified example. Different endpoints can generate different HTML in some cases, so we want to be able to exercise different API endpoints for the same Markdown. By default, the /markdown endpoint is used.

glfm_specification/input/gitlab_flavored_markdown/glfm_example_metadata.yml sample entries:

---
08_01_00__examples_using_internal_extensions__markdown_preview_api_request_overrides__001:
  api_request_override_path: /groups/glfm_group/preview_markdown
08_01_00__examples_using_internal_extensions__markdown_preview_api_request_overrides__002:
  api_request_override_path: /glfm_group/glfm_project/preview_markdown
08_01_00__examples_using_internal_extensions__markdown_preview_api_request_overrides__003:
  api_request_override_path: /glfm_group/glfm_project/preview_markdown
08_01_00__examples_using_internal_extensions__markdown_preview_api_request_overrides__004:
  api_request_override_path: /-/snippets/preview_markdown
08_01_00__examples_using_internal_extensions__markdown_preview_api_request_overrides__005:
  api_request_override_path: /glfm_group/glfm_project/-/wikis/new_page/preview_markdown
08_01_00__examples_using_internal_extensions__markdown_preview_api_request_overrides__006:
  ee: true
  api_request_override_path: /groups/glfm_group/-/wikis/new_page/preview_markdown

Output specification files

The glfm_specification/output directory contains the CommonMark standard format spec.txt file which represents the GLFM specification which is generated by the update-specification.rb script. It also contains the rendered spec.html which is generated based on the spec.txt as input.

These output spec.* files, which represent the GLFM specification, are colocated under the same parent folder glfm_specification with the other input specification files. They're located here both for convenience, and because they are all a mix of manually edited and generated files.

In GFM, spec.txt is located in the test dir, and in CommonMark it's located in the project root. No precedent exists for a standard location. In the future, we may decide to move or copy a hosted version of the rendered HTML spec.html version to another location or site.

spec.txt

glfm_specification/output_spec/spec.txt is a Markdown specification file, in the standard format with prose and Markdown + canonical HTML examples.

In the GLFM specification, spex.txt only contains the official specifiaction examples from glfm_official_specification.md. It does not contain the internal extension examples from glfm_internal_extensions.md.

It also serves as input for other scripts such as run-spec-tests.sh.

It is generated or updated by the update-specification.rb script, using the input specification files as input. See the update-specification.rb script section for a diagram and more description on this process.

NOTE: Even though spec.txt is a Markdown file, it is named with a *.txt extension for consistency with the GFM and CommonMark specifications. All other GLFM Markdown files are named with a *.md extension for compatibility with various editors to enable Markdown formatting and syntax highlighting.

spec.html

glfm_specification/output_spec/spec.html is an HTML file, rendered based on spec.txt. It is generated (or updated) by the update-specification.rb script at the same time as spec.txt.

It corresponds to the HTML-rendered versions of the "GitHub Flavored Markdown" (GFM) specification and the CommonMark specification, but only contains GitLab Flavored Markdown (GLFM) examples.

NOTE:

The formatting of this HTML is currently not identical to the GFM and CommonMark HTML-rendered specification. It is only the raw output of running spec.txt through the GitLab Markdown renderer. Properly formatting the HTML will require duplicating or reusing the Lua script and template from the CommonMark project: CommonMark Makefile

Output example snapshot files

The output_example_snapshots directory contains files which are generated by the update-specification.rb and update-example-snapshots.rb scripts based off of the files in the glfm_specification/input directory.

The output-specification.rb script generates output_snapshot_examples/snapshot_spec.md and output_snapshot_examples/snapshot_spec.html. These files are Markdown specification files containing examples generated based on input files, similar to the output_spec/spec.txt and output_spec/spec.html, with the following differences:

  1. They contain a superset of all examples from the CommonMark, GitHub Flavored Markdown, and GitLab Flavored Markdown specifications, whereas spec.* only contains the GLFM specification. This is to provide a single place to refer to all examples when working with snapshot testing.
  2. They contain only header sections which contain examples. They do not contain any prose-only sections which do not contain examples.

The update-example-snapshots.rb script generates the various output_snapshot_examples/*.yml files, which are used as fixtures to drive the snapshot testing.

After the entire GLFM implementation is complete for both backend (Ruby) and frontend (JavaScript), all of these YAML files can be automatically generated. However, while the implementations are still in progress, the skip_update_example_snapshots key in glfm_specification/input/gitlab_flavored_markdown/glfm_example_status.yml can be used to disable automatic generation of some examples. They can instead be manually edited as necessary to help drive the implementations.

snapshot_spec.md

glfm_specification/output_example_snapshots/snapshot_spec.md is a Markdown file, containing standard Markdown + canonical HTML examples like spec.txt.

It is generated or updated by the update-specification.rb script, using the input specification files as input. See the update-specification.rb script section for a diagram and more description on this process. It also serves as input for other scripts such as update-example-snapshots.rb.

It is similar to spec.txt, with the following differences:

  1. spec.txt contains only examples for GitLab Flavored Markdown, but snapshot_spec.md also contains the full superset of examples from the "GitHub Flavored Markdown" (GFM)specification and the CommonMark specification specifications.
  2. spec.txt represents the full GLFM specification, including additional header sections containing only explanatory prose and no examples, but snapshot_spec.md consists of only header sections which contain examples. This is because its purpose is to serve as input for the other output example snapshot files - it is not intended to serve as an actual specification file like spec.txt or spec.html.
snapshot_spec.html

glfm_specification/output_snapshot_examples/snapshot_spec.html is an HTML file, rendered based on snapshot_spec.md. It is generated (or updated) by the update-specification.rb script at the same time as snapshot_spec.md.

NOTE: The formatting of this HTML is currently not identical to the GFM and CommonMark HTML-rendered specification. It is only the raw output of running snapshot_spec.md through the GitLab Markdown renderer. Properly formatting the HTML will require duplicating or reusing the Lua script and template from the CommonMark project: CommonMark Makefile

examples_index.yml

glfm_specification/output_example_snapshots/examples_index.yml is the main list of all CommonMark, GFM, and GLFM example names, each with a uniquely identifying name.

  • It is generated from the hierarchical sections and examples in the GFM spec.txt specification.
  • For CommonMark and GFM examples, these sections originally came from the GFM spec.txt.
  • For GLFM examples, it is generated from glfm_official_specification.md and glfm_internal_extensions.md.
  • It also contains extra metadata about each example, such as:
    1. spec_example_position - The position of the example in the generated GLFM spec.txt file.
      • This value is the index order of each individual Markdown + HTML5 example in the file. It is not the line number in the file.
      • This value can be used to locate the example in the rendered spec.html file, because the standard CommonMark tooling includes the index number for each example in the rendered HTML file. For example: https://spec.commonmark.org/0.30/#example-42
    2. source_specification - Which specification the example originally came from: commonmark, github, or gitlab.
  • The naming convention for example entry names is based on nested header section names and example index in the header.
    • This naming convention should result in fairly stable names and example positions. The CommonMark / GLFM specification rarely changes, and most GLFM examples where multiple examples exist for the same Section 7 subsection are added to the end of the sub-section.

examples_index.yml sample entries:

02_01_00_preliminaries_characters_and_lines_1:
  spec_example_position: 1
  source_specification: commonmark
03_01_00_blocks_and_inlines_precedence_1:
  spec_example_position: 12
  source_specification: commonmark
05_03_00_container_blocks_task_list_items_1:
  spec_example_position: 279
  source_specification: github
06_04_00_inlines_emphasis_and_strong_emphasis_1:
  spec_example_position: 360
  source_specification: github
07_01_00_audio_link_1:
  spec_example_position: 301
  source_specification: gitlab
markdown.yml

glfm_specification/output_example_snapshots/markdown.yml contains the original Markdown for each entry in glfm_specification/output_example_snapshots/examples_index.yml:

glfm_specification/output_example_snapshots/markdown.yml sample entry:

06_04_00_inlines_emphasis_and_strong_emphasis_1: |
  *foo bar*
html.yml

glfm_specification/output_example_snapshots/html.yml contains the HTML for each entry in glfm_specification/output_example_snapshots/examples_index.yml:

Three types of entries exist, with different HTML for each:

  • Canonical
  • Static
    • This is the static (backend (Ruby)-generated) HTML for each entry in glfm_specification/output_example_snapshots/examples_index.yml.
    • It is generated/updated from backend Markdown API (or the underlying internal classes) via the update-example-snapshots.rb script, but can be manually updated for static examples with incomplete implementations.
  • WYSIWYG
    • The WYSIWYG (frontend, JavaScript-generated) HTML for each entry in glfm_specification/output_example_snapshots/examples_index.yml.
    • It is generated (or updated) from the frontend rich text editor implementation via the update-example-snapshots.rb script. It can be manually updated for WYSIWYG examples with incomplete implementations.

Any exceptions or failures which occur when generating HTML are replaced with an Error - check implementation value.

glfm_specification/output_example_snapshots/html.yml sample entry:

06_04_00_inlines_emphasis_and_strong_emphasis_1:
  canonical: |
    <p><em>foo bar</em></p>
  static: |
    <p data-sourcepos="1:1-1:9" dir="auto"><strong>foo bar</strong></p>
  wysiwyg: |
    <p><strong>foo bar</strong></p>

NOTE: The actual static or WYSIWYG entries may differ from the example html.yml, depending on how the implementations evolve.

prosemirror_json.yml

glfm_specification/output_example_snapshots/prosemirror_json.yml contains the ProseMirror JSON for each entry in glfm_specification/output_example_snapshots/examples_index.yml

  • It is generated (or updated) from the frontend code via the update-example-snapshots.rb script, but can be manually updated for examples with incomplete implementations.
  • Any exceptions or failures when generating are replaced with a Error - check implementation value.

glfm_specification/output_example_snapshots/prosemirror_json.yml sample entry:

06_04_00_inlines_emphasis_and_strong_emphasis_1: |-
  {
    "type": "doc",
    "content": [
      {
        "type": "paragraph",
        "content": [
          {
            "type": "text",
            "marks": [
              {
                "type": "bold"
              }
            ],
            "text": "foo bar"
          },
        ]
      },
    ]
  }

Workflows

This section describes how the scripts can be used to manage the GLFM specification and tests.

Update the GLFM specification and run conformance tests

  1. Run update-specification.rb to update the GLFM specification output specification files.
  2. Visually inspect and confirm any resulting changes to the output specification files.
  3. Run run-spec-tests.sh. This script is not yet implemented and only prints a placeholder message. When implemented, it should run the conformance tests against the canonicalized GLFM specification.
  4. Commit any changes to the output specification files.

Update the example snapshots and run snapshot tests

  1. If you are working on an in-progress feature or bug, make any necessary manual updates to the input specification files. This may include:
    1. Updating the canonical Markdown or HTML examples in glfm_official_specification.md or glfm_internal_extensions.md.
    2. Updating glfm_specification/input/gitlab_flavored_markdown/glfm_example_status.yml to reflect the current status of the examples or tests.
  2. Run update-specification.rb to update the spec.txt to reflect any changes which were made to the input specification files.
  3. Visually inspect and confirm any resulting changes to the output specification files.
  4. Run update-example-snapshots.rb to update the example snapshot files.
  5. Visually inspect and confirm any resulting changes to the example snapshot files.
  6. Run run-snapshot-tests.sh as a convenience script to run all relevant frontend (RSpec) and backend (Jest) tests which use the example snapshots.
    1. Any frontend or backend snapshot test may also be run individually.
    2. All frontend and backend tests are also run as part of the continuous integration suite, as they typically are.
  7. Commit any changes to the input specification files, output specification files, or example snapshot files.