Bug 1708293 - [lint] Add a linter to prefer multiline skip-if statements in test manifests, r=releng-reviewers,jmaher

This will warn if someone includes something like:

    skip-if = <condition A> || <condition B>  # reason A is skipped; reason B is skipped

Instead they should use:

    skip-if =
        <condition A>  # reason A is skipped
        <condition B>  # reason B is skipped

Differential Revision: https://phabricator.services.mozilla.com/D113707

taskcluster/ci/source-test/mozlint.yml

@@ -243,7 +243,7 @@ test-manifest:
     treeherder:
         symbol: misc(tm)
     run:
-        mach: lint -v -l test-disable -f treeherder -f json:/builds/worker/mozlint.json *
+        mach: lint -v -l test-manifest-disable -l test-manifest-skip-if -f treeherder -f json:/builds/worker/mozlint.json *
     when:
         files-changed:
             - '**/*.ini'

tools/lint/test-manifest-skip-if.yml

@@ -0,0 +1,18 @@
+---
+multiline-skip-if:
+    description: Conditions joined by || should be on separate lines
+    hint: |
+        skip-if =
+            <condition one>  # reason
+            <condition two>  # reason
+    exclude:
+        - "**/application.ini"
+        - "**/l10n.ini"
+        - dom/canvas/test/webgl-conf/mochitest-errata.ini
+        - testing/mozbase/manifestparser/tests
+        - testing/web-platform
+        - xpcom/tests/unit/data
+    extensions: ['ini']
+    level: warning
+    type: regex
+    payload: '^\s*(skip|fail)-if\s*=[^(]*\|\|'