Add link to git commit for unstable changelog too (#2078)

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

changelogs/internal/newsfragments/2078.clarification

@@ -0,0 +1 @@
+Add link to the git commit for the unstable changelog.

layouts/docs/changelog.html

@@ -31,9 +31,17 @@
     <h1>{{ .Title }}</h1>
 
     <table class="release-info">
-        {{ if ne $version "unstable" -}}
-            {{ $commitLink := printf "https://github.com/matrix-org/matrix-spec/tree/%s" $version -}}
+        {{ $rev := $version }}
+        {{ if eq $version "unstable" -}}
+            {{- /*
+                Extract the git SHA from the frontmatter of the changelog, where
+                it was stashed by `generate-changelog.sh`.
+            */ -}}
+            {{ $rev = .Params.commit -}}
+        {{ end -}}
+        {{ $commitLink := printf "https://github.com/matrix-org/matrix-spec/tree/%s" $rev -}}
         <tr><th>Git commit</th><td><a href="{{ $commitLink }}">{{ $commitLink }}</a></td>
+        {{ if ne $version "unstable" }}
         <tr><th>Release date</th><td>{{ .Date | time.Format ":date_long" }}</td>
         {{ end -}}
         {{ $checklist := .OutputFormats.Get "checklist" -}}

scripts/generate-changelog.sh

@@ -44,8 +44,18 @@ outputs:
   - html
   - checklist
 date: $(date -Idate)
----
 EOF
+
+    # Add the commit hash for the unstable versions. It is used to generate a
+    # link to the commit on the repository.
+    if [ "$VERSION" == "vUNSTABLE" ]; then
+        echo "params:"
+        echo "  commit: $(git rev-parse --short HEAD)"
+    fi
+
+    # Close the frontmatter.
+    echo "---"
+
     # Remove trailing whitespace (such as our intentionally blank RST headings)
     sed -e "s/[ ]*$//" rendered.md
 } > ../content/changelog/$FILENAME