GitHub Action: Check local Markdown links on push (#2067)

Adds an GitHub Action to check all local (non http://, https:// ) links in all Markdown files of the repository for liveness.
Fails if a file is not found.

# Goal
This should help maintaining the quality of the documentation.

# Impact
Takes ~24 seconds currently and found 3 dead links (pull requests already created).

# Dependent PRs
* #2064 
* #2065 
* #2066

# Info
See [markdown-link-check](https://github.com/marketplace/actions/markdown-link-check).

# Example output
```
FILE: ./docs/profiling.md

1 links checked.

FILE: ./docs/plugins_guidelines.md

37 links checked.

FILE: ./docs/linters.md
[✖] ../.github/linters/markdown-lint.yml → Status: 400 [Error: ENOENT: no such file or directory, access '/github/workspace/.github/linters/markdown-lint.yml'] {
  errno: -2,
  code: 'ENOENT',
  syscall: 'access',
  path: '/github/workspace/.github/linters/markdown-lint.yml'
}
```

# Improvements
* Can also be used to check external links, but fails because of:
  * Too many requests (429) responses:
```
FILE: ./CHANGELOG.md
[✖] https://github.com/bevyengine/bevy/pull/1762 → Status: 429
```
   * crates.io links respond 404
```
FILE: ./README.md
[✖] https://crates.io/crates/bevy → Status: 404
```

.github/bors.toml

@@ -7,6 +7,7 @@ status = [
     "build-wasm (nightly, ubuntu-latest)",
     "build-android",
     "markdownlint",
+    "check-markdown-links",
     "run-examples",
     "check-doc",
 ]

.github/linters/markdown-link-check.json

@@ -0,0 +1,21 @@
+{
+  "ignorePatterns": [
+    {
+      "pattern": "^https?://github\\.com/"
+    }
+  ],
+  "replacementPatterns": [],
+  "httpHeaders": [
+    {
+      "urls": ["https://crates.io"],
+      "headers": {
+        "Accept": "text/html"
+      }
+    }
+  ],
+  "timeout": "20s",
+  "retryOn429": true,
+  "retryCount": 5,
+  "fallbackRetryDelay": "30s",
+  "aliveStatusCodes": [200, 206]
+}

.github/workflows/ci.yml

@@ -93,6 +93,16 @@ jobs:
           # Not needed here as only one Linter is used.
           #GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
+  check-markdown-links:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - uses: gaurav-nelson/github-action-markdown-link-check@0fe4911067fa322422f325b002d2038ba5602170
+      with:
+        use-quiet-mode: 'yes'
+        use-verbose-mode: 'yes'
+        config-file: '.github/linters/markdown-link-check.json'
+
   run-examples:
     runs-on: ubuntu-latest
 

docs/linters.md

@@ -28,7 +28,7 @@ Explanation:
 ### [markdownlint](https://github.com/DavidAnson/markdownlint)
 
 `markdownlint` is provided by `super-linter` and is responsible for `.md` files.
-Its configuration is saved in the [.markdown-lint.yml](../.github/linters/markdown-lint.yml) file.
+Its configuration is saved in the [.markdown-lint.yml](../.github/linters/.markdown-lint.yml) file.
 
 The provided rules are documented [here](https://github.com/DavidAnson/markdownlint/blob/main/doc/Rules.md) and information about setting the config can be seen [here](https://github.com/DavidAnson/markdownlint#optionsconfig).
 

examples/README.md

@@ -280,7 +280,9 @@ Please reference `cargo-apk` [README](https://crates.io/crates/cargo-apk) for ot
 
 ### Old phones
 
-Bevy by default targets Android API level 29 in its examples which is the [Play Store's minimum API to upload or update apps](https://developer.android.com/distribute/best-practices/develop/target-sdk). Users of older phones may want to use an older API when testing.
+Bevy by default targets Android API level 29 in its examples which is the <!-- markdown-link-check-disable -->
+[Play Store's minimum API to upload or update apps](https://developer.android.com/distribute/best-practices/develop/target-sdk). <!-- markdown-link-check-enable -->
+Users of older phones may want to use an older API when testing.
 
 To use a different API, the following fields must be updated in Cargo.toml: