From 990f3e4b97756bc6941c8d36f6387c33d2bf10c8 Mon Sep 17 00:00:00 2001
From: Aliaksandr <grubian2@gmail.com>
Date: Wed, 17 Jun 2026 00:43:05 +0300
Subject: [PATCH] ci/eval: name the base branch in the performance comparison
 summary

The performance comparison summary previously stated it compared against
"its pull request base branch (e.g., 'master')" regardless of the actual
base branch.

Plumb the base branch classification computed in prepare.js through the
eval workflow to the `compare` derivation so the summary names the real
base branch (e.g. "staging-25.11"). The local `eval.full` helper defaults
to "master", matching its touched-files convention.

Assisted-by: claude-code with claude-opus-4-8[1m]-high
(cherry picked from commit a100d091a07cccbfbc2440fdc4a9de4b261e04f4)
---
 .github/workflows/eval.yml                | 5 +++++
 .github/workflows/merge-group.yml         | 1 +
 .github/workflows/pull-request-target.yml | 1 +
 ci/eval/compare/default.nix               | 3 ++-
 ci/eval/default.nix                       | 5 ++++-
 5 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/eval.yml b/.github/workflows/eval.yml
index dd2ea029dcd6..0b576a464220 100644
--- a/.github/workflows/eval.yml
+++ b/.github/workflows/eval.yml
@@ -15,6 +15,9 @@ on:
       targetSha:
         required: true
         type: string
+      baseBranch:
+        required: true
+        type: string
       systems:
         required: true
         type: string
@@ -291,6 +294,7 @@ jobs:
       - name: Compare against the target branch
         env:
           TARGET_SHA: ${{ inputs.mergedSha }}
+          BASE_BRANCH: ${{ fromJSON(inputs.baseBranch).branch }}
         run: |
           git -C nixpkgs/trusted diff --name-only "$TARGET_SHA" \
             | jq --raw-input --slurp 'split("\n")[:-1]' > touched-files.json
@@ -299,6 +303,7 @@ jobs:
           nix-build nixpkgs/trusted/ci --arg nixpkgs ./nixpkgs/trusted-pinned -A eval.compare \
             --arg combinedDir ./combined \
             --arg touchedFilesJson ./touched-files.json \
+            --argstr baseBranch "$BASE_BRANCH" \
             --out-link comparison
 
           cat comparison/step-summary.md >> "$GITHUB_STEP_SUMMARY"
diff --git a/.github/workflows/merge-group.yml b/.github/workflows/merge-group.yml
index 6ff67aefae60..196bf3040068 100644
--- a/.github/workflows/merge-group.yml
+++ b/.github/workflows/merge-group.yml
@@ -97,6 +97,7 @@ jobs:
       artifact-prefix: ${{ inputs.artifact-prefix }}
       mergedSha: ${{ needs.prepare.outputs.mergedSha }}
       targetSha: ${{ needs.prepare.outputs.targetSha }}
+      baseBranch: ${{ needs.prepare.outputs.baseBranch }}
       systems: ${{ needs.prepare.outputs.systems }}
 
   build:
diff --git a/.github/workflows/pull-request-target.yml b/.github/workflows/pull-request-target.yml
index 8edde367c13b..d4fda08d2e01 100644
--- a/.github/workflows/pull-request-target.yml
+++ b/.github/workflows/pull-request-target.yml
@@ -110,6 +110,7 @@ jobs:
       mergedSha: ${{ needs.prepare.outputs.mergedSha }}
       headSha: ${{ github.event.pull_request.head.sha }}
       targetSha: ${{ needs.prepare.outputs.targetSha }}
+      baseBranch: ${{ needs.prepare.outputs.baseBranch }}
       systems: ${{ needs.prepare.outputs.systems }}
       testVersions: ${{ contains(fromJSON(needs.prepare.outputs.touched), 'pinned') && !contains(fromJSON(needs.prepare.outputs.headBranch).type, 'development') }}
 
diff --git a/ci/eval/compare/default.nix b/ci/eval/compare/default.nix
index 26cc12487155..057331e0f05b 100644
--- a/ci/eval/compare/default.nix
+++ b/ci/eval/compare/default.nix
@@ -49,6 +49,7 @@ in
 {
   combinedDir,
   touchedFilesJson,
+  baseBranch,
   ownersFile ? ../../OWNERS,
 }:
 let
@@ -240,7 +241,7 @@ runCommand "compare"
       echo
       echo "# Performance comparison"
       echo
-      echo "This compares the performance of this branch against its pull request base branch (e.g., 'master')"
+      echo "This compares the performance of this branch against the \`${baseBranch}\` branch."
       echo
     } >> $out/step-summary.md
 
diff --git a/ci/eval/default.nix b/ci/eval/default.nix
index 7c0a2e9f3139..2e8bec41ca5d 100644
--- a/ci/eval/default.nix
+++ b/ci/eval/default.nix
@@ -288,6 +288,9 @@ let
       #   | jq --raw-input --slurp 'split("\n")[:-1]' > touched-files.json
       # ```
       touchedFilesJson ? builtins.toFile "touched-files.json" "[ ]",
+      # The branch the local comparison is made against; matches the `master`
+      # used in the touched-files expression above.
+      baseBranch ? "master",
     }:
     let
       diffs = symlinkJoin {
@@ -305,7 +308,7 @@ let
       };
       comparisonReport = compare {
         combinedDir = combine { diffDir = diffs; };
-        inherit touchedFilesJson;
+        inherit touchedFilesJson baseBranch;
       };
     in
     comparisonReport;