fix(actions): make cancelled() work in job if evaluation (#38495) (#38497)

Backport #38495 by @Zettat123

Fix #38485

#37478 moved `if` evaluation from runner to server. But `NewInterpeter`
always provides a nil `JobContext` for the evaluator, which makes
[`cancelled()`](https://gitea.com/gitea/runner/src/commit/ad967330a8788c9b8ab723abbc1a86d53c3bc5e6/act/exprparser/functions.go#L299)
panic on `Job.Status` because `Job` is a nil pointer.

Co-authored-by: Zettat123 <zettat123@gmail.com>

modules/actions/jobparser/interpeter.go

@@ -57,9 +57,14 @@ func NewInterpeter(
 	}
 
 	ee := &exprparser.EvaluationEnvironment{
-		Github:   gitCtx,
+		Github: gitCtx,
-		Env:      nil, // no need
+		Env:    nil, // no need
-		Job:      nil, // no need
+		// Job must be non-nil because cancelled() dereferences Job.Status unconditionally.
+		// See: https://gitea.com/gitea/runner/src/commit/ad967330a8788c9b8ab723abbc1a86d53c3bc5e6/act/exprparser/functions.go#L299
+		// TODO: The empty JobContext.Status is right for now because Gitea never checks `if` condition when the workflow run is cancelled.
+		// This is an implementation gap in Gitea Actions. When a workflow run is cancelled, Gitea should check the job's `if` condition,
+		// and if the condition is met (e.g. `if: ${{ cancelled() }}` ), the job should be executed rather than cancelled.
+		Job:      &model.JobContext{},
 		Steps:    nil, // no need
 		Runner:   nil, // no need
 		Secrets:  nil, // no need

modules/actions/jobparser/model_test.go

@@ -464,3 +464,61 @@ func TestParseMappingNode(t *testing.T) {
 		})
 	}
 }
+
+func TestEvaluateJobIfExpression(t *testing.T) {
+	kases := []struct {
+		name       string
+		ifCond     string
+		needResult string
+		expected   bool
+	}{
+		{name: "empty need success", ifCond: "${{ 1 == 1 }}", needResult: "success", expected: true},
+		{name: "always", ifCond: "${{ always() }}", needResult: "failure", expected: true},
+		{name: "failure true", ifCond: "${{ failure() }}", needResult: "failure", expected: true},
+		{name: "failure false", ifCond: "${{ failure() }}", needResult: "success", expected: false},
+		{name: "success true", ifCond: "${{ success() }}", needResult: "success", expected: true},
+		// cancelled() is always false on the server: a cancelled run never evaluates a blocked job's `if:`
+		{name: "cancelled", ifCond: "${{ cancelled() }}", needResult: "success", expected: false},
+		{name: "not cancelled or failure", ifCond: "${{ !(cancelled() || failure()) }}", needResult: "success", expected: true},
+		{name: "not cancelled or failure, need failed", ifCond: "${{ !(cancelled() || failure()) }}", needResult: "failure", expected: false},
+	}
+	for _, kase := range kases {
+		t.Run(kase.name, func(t *testing.T) {
+			content := strings.ReplaceAll(`
+name: test
+on: push
+jobs:
+  job1:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo job1
+  job2:
+    runs-on: ubuntu-latest
+    needs: [job1]
+    if: IF_COND
+    steps:
+      - run: echo job2
+`, "IF_COND", kase.ifCond)
+
+			workflows, err := Parse([]byte(content))
+			require.NoError(t, err)
+
+			var job2 *Job
+			for _, wf := range workflows {
+				if id, job := wf.Job(); id == "job2" {
+					job2 = job
+				}
+			}
+			require.NotNil(t, job2)
+
+			// mirrors findJobNeedsAndFillJobResults: the needs' results plus a self entry carrying Needs
+			results := map[string]*JobResult{
+				"job1": {Result: kase.needResult},
+				"job2": {Needs: []string{"job1"}},
+			}
+			got, err := EvaluateJobIfExpression("job2", job2, map[string]any{}, results, nil, nil)
+			require.NoError(t, err)
+			assert.Equal(t, kase.expected, got)
+		})
+	}
+}