fix(actions): support matrix when evaluating workflow if expression (#38474) (#38557)

Backport #38474 by @Zettat123

Partially fixes #38466

Added `matrix` to the evaluator for `if` expressions

Signed-off-by: Zettat123 <zettat123@gmail.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>
Co-authored-by: bircni <bircni@icloud.com>

modules/actions/jobparser/model.go

@@ -490,7 +490,19 @@ func EvaluateJobIfExpression(jobID string, job *Job, gitCtx map[string]any, resu
 			RawMatrix:         job.Strategy.RawMatrix,
 		},
 	}
-	evaluator := NewExpressionEvaluator(NewInterpeter(jobID, actJob, nil, toGitContext(gitCtx), results, vars, inputs))
+	// Each per-matrix job carries its single matrix combination in RawMatrix so resolve it and pass it in;
+	// otherwise `matrix.*` references in `if:` evaluate to null.
+	// GetMatrixes always returns at least one element (an empty map for a job without a matrix),
+	// so only a non-empty combination should populate `matrix.*`, leaving it nil otherwise.
+	var matrix map[string]any
+	matrixes, err := actJob.GetMatrixes()
+	if err != nil {
+		return false, err
+	}
+	if len(matrixes) > 0 && len(matrixes[0]) > 0 {
+		matrix = matrixes[0]
+	}
+	evaluator := NewExpressionEvaluator(NewInterpeter(jobID, actJob, matrix, toGitContext(gitCtx), results, vars, inputs))
 	expr, err := rewriteSubExpression(job.If.Value, false)
 	if err != nil {
 		return false, err

modules/actions/jobparser/model_test.go

@@ -4,6 +4,7 @@
 package jobparser
 
 import (
+	"fmt"
 	"strings"
 	"testing"
 
@@ -465,6 +466,51 @@ func TestParseMappingNode(t *testing.T) {
 	}
 }
 
+func TestEvaluateJobIfExpressionMatrix(t *testing.T) {
+	ifExprs := []string{
+		`${{ contains(fromJSON('["linux","windows"]'), matrix.target) }}`,
+		`${{ contains('["linux","windows"]', matrix.target) }}`,
+	}
+
+	want := map[string]bool{
+		"build (linux)":   true,
+		"build (windows)": true,
+		"build (macos)":   false,
+	}
+
+	for _, ifExpr := range ifExprs {
+		t.Run(ifExpr, func(t *testing.T) {
+			content := fmt.Sprintf(`
+name: test
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: %s
+    strategy:
+      fail-fast: false
+      matrix:
+        target: [linux, windows, macos]
+    steps:
+      - run: echo ${{ matrix.target }}
+`, ifExpr)
+
+			swfs, err := Parse([]byte(content))
+			require.NoError(t, err)
+			require.Len(t, swfs, 3)
+
+			got := make(map[string]bool, len(swfs))
+			for _, swf := range swfs {
+				id, job := swf.Job()
+				shouldRun, err := EvaluateJobIfExpression(id, job, map[string]any{}, map[string]*JobResult{id: {}}, nil, nil)
+				require.NoError(t, err)
+				got[job.Name] = shouldRun
+			}
+			assert.Equal(t, want, got)
+		})
+	}
+}
+
 func TestEvaluateJobIfExpression(t *testing.T) {
 	kases := []struct {
 		name       string