From 481b5376af8b54f02829c5f77a09981bd26e47bf Mon Sep 17 00:00:00 2001
From: Lucas Weatherhog <31103312+weatherhog@users.noreply.github.com>
Date: Thu, 2 Jul 2026 10:49:32 +0200
Subject: [PATCH] feat(yaml-diff): colourise diff output via ```diff fenced
 block
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GitHub PR comments can't render ANSI, so colour the semantic diff using
the `diff` code-fence highlighter instead: switch the fence to ```diff,
move dyff's indented go-patch `-`/`+` markers to column 0 (keeping the
indent after the marker) so removed/added values render red/green, and
emit each file header as `@@ <path> @@` for a coloured separator.

The sed rewrite only reorders leading whitespace, so byte counts — and
the per-file/total truncation caps computed earlier — are unchanged.
dyff's own colour stays off (auto-off in CI); we rely purely on GitHub's
syntax highlighting.

Requested in giantswarm/roadmap#4121.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 .github/workflows/yaml-diff.yaml | 13 ++++++++++---
 CHANGELOG.md                     |  6 ++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/yaml-diff.yaml b/.github/workflows/yaml-diff.yaml
index 6119271..747f2cc 100644
--- a/.github/workflows/yaml-diff.yaml
+++ b/.github/workflows/yaml-diff.yaml
@@ -188,7 +188,7 @@ jobs:
             section=$(mktemp)
             {
               echo
-              echo "=== ${path} ==="
+              echo "@@ ${path} @@"
               cat /tmp/yaml-diff/file-diff
             } > "${section}"
 
@@ -227,8 +227,15 @@ jobs:
               echo "<summary>Output</summary>"
               echo "<!-- mandatory empty line -->"
               echo
-              echo '```'
-              cat /tmp/yaml-diff/body
+              echo '```diff'
+              # GitHub colours a `diff` fence by line prefix: `-` red, `+` green,
+              # `@@ … @@` header. dyff go-patch prefixes changed values with an
+              # *indented* `-`/`+`; move the marker to column 0 while keeping the
+              # original indent *after* it, so the highlighter fires and nesting is
+              # still visible. The rewrite only reorders leading whitespace, so byte
+              # counts (and the truncation maths above) are unchanged. dyff colour
+              # stays off (auto-off in CI) — comments cannot render ANSI.
+              sed -E 's/^([[:space:]]*)([+-])([[:space:]].*)$/\2\1\3/' /tmp/yaml-diff/body
               echo '```'
               echo "</details>"
               echo "<!-- mandatory empty line -->"
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f62d6cc..b389716 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 however this project does not use Semantic Versioning and there are no releases.
 Instead this file uses a date-based structure.
 
+## 2026-07-02
+
+### Changed
+
+- `yaml-diff.yaml` now posts its `dyff` output inside a ` ```diff ` fenced block so GitHub colourises it — removed values render red, added values green, and each file gets a `@@ … @@` header. dyff's go-patch `-`/`+` markers are moved to column 0 (indentation preserved after the marker) so the highlighter picks them up; the rewrite only reorders leading whitespace, so the comment-size truncation limits are unaffected. dyff's own ANSI colour stays disabled (comments can't render it). Requested in giantswarm/roadmap#4121.
+
 ## 2026-06-30
 
 ### Fixed