Add yamllint (#5129)

.github/workflows/matchers/yamllint.json

@@ -0,0 +1,22 @@
+{
+    "problemMatcher": [
+      {
+        "owner": "yamllint",
+        "pattern": [
+          {
+            "regexp": "^(.*\\.ya?ml)$",
+            "file": 1
+          },
+          {
+            "regexp": "^\\s{2}(\\d+):(\\d+)\\s+(error|warning)\\s+(.*?)\\s+\\((.*)\\)$",
+            "line": 1,
+            "column": 2,
+            "severity": 3,
+            "message": 4,
+            "code": 5,
+            "loop": true
+          }
+        ]
+      }
+    ]
+  }

.github/workflows/monthly.yml

@@ -1,6 +1,6 @@
 name: Bump our Calendar Version
 
-on:
+on: # yamllint disable-line rule:truthy
   workflow_dispatch:
   schedule:
     - cron: "30 3 1 * *"

.github/workflows/onPush.yml

@@ -1,6 +1,6 @@
 name: On Push
 
-on:
+on: # yamllint disable-line rule:truthy
   workflow_dispatch:
     inputs:
       beta:

.github/workflows/pr.yml

@@ -1,14 +1,26 @@
 name: Pull Request
 
-on:
+on: # yamllint disable-line rule:truthy
   pull_request:
     branches: [master]
 
 jobs:
+  yamllint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Register yamllint problem matcher
+        run: |
+          echo "::add-matcher::.github/workflows/matchers/yamllint.json"
+
+      - name: Validate YAML
+        run: yamllint --strict --format github .
+
   ktlint:
     runs-on: ubuntu-latest
     permissions:
-        security-events: write
+      security-events: write
     steps:
       - uses: actions/checkout@v4
 
@@ -146,7 +158,6 @@ jobs:
           emulator-options: -no-window -gpu swiftshader_indirect -noaudio -no-boot-anim -camera-back none
           script: echo "Generated AVD snapshot for caching."
 
-
       - name: Build projects and run instrumentation tests
         uses: reactivecircus/android-emulator-runner@v2
         with:

.github/workflows/release.yml

@@ -1,6 +1,6 @@
 name: Production Deploy
 
-on:
+on: # yamllint disable-line rule:truthy
   workflow_dispatch:
   release:
     types: [released]

.github/workflows/weekly.yml

@@ -1,6 +1,6 @@
 name: Tag Weekly Release
 
-on:
+on: # yamllint disable-line rule:truthy
   workflow_dispatch:
   schedule:
     - cron: "0 4 * * 0"

.yamllint

@@ -0,0 +1,59 @@
+rules:
+  braces:
+    level: error
+    min-spaces-inside: 0
+    max-spaces-inside: 1
+    min-spaces-inside-empty: -1
+    max-spaces-inside-empty: -1
+  brackets:
+    level: error
+    min-spaces-inside: 0
+    max-spaces-inside: 0
+    min-spaces-inside-empty: -1
+    max-spaces-inside-empty: -1
+  colons:
+    level: error
+    max-spaces-before: 0
+    max-spaces-after: 1
+  commas:
+    level: error
+    max-spaces-before: 0
+    min-spaces-after: 1
+    max-spaces-after: 1
+  comments:
+    level: error
+    require-starting-space: true
+    min-spaces-from-content: 1
+  comments-indentation:
+    level: error
+  document-end:
+    level: error
+    present: false
+  document-start:
+    level: error
+    present: false
+  empty-lines:
+    level: error
+    max: 1
+    max-start: 0
+    max-end: 1
+  hyphens:
+    level: error
+    max-spaces-after: 1
+  indentation:
+    level: error
+    spaces: 2
+    indent-sequences: true
+    check-multi-line-strings: false
+  key-duplicates:
+    level: error
+  line-length: disable
+  new-line-at-end-of-file:
+    level: error
+  new-lines:
+    level: error
+    type: unix
+  trailing-spaces:
+    level: error
+  truthy:
+    level: error