Improve the handling of jobs.<job_id>.if (#31070)

Fix #25897
Fix #30322

#29464 cannot handle some complex `if` conditions correctly because it
only checks `always()` literally. In fact, it's not easy to evaluate the
`if` condition on the Gitea side because evaluating it requires a series
of contexts. But act_runner is able to evaluate the `if` condition
before running the job (for more information, see
[`gitea/act`](517d11c671/pkg/runner/run_context.go (L739-L753)))
. So we can use act_runner to check the `if` condition.

In this PR, how to handle a blocked job depends on its `needs` and `if`:
- If not all jobs in `needs` completed successfully and the job's `if`
is empty, set the job status to `StatusSkipped`
- In other cases, the job status will be set to `StatusWaiting`, and
then act_runner will check the `if` condition and run the job if the
condition is met

services/actions/job_emitter.go

@@ -7,7 +7,6 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"strings"
 
 	actions_model "code.gitea.io/gitea/models/actions"
 	"code.gitea.io/gitea/models/db"
@@ -141,18 +140,19 @@ func (r *jobStatusResolver) resolve() map[int64]actions_model.Status {
 			if allSucceed {
 				ret[id] = actions_model.StatusWaiting
 			} else {
-				// If a job's "if" condition is "always()", the job should always run even if some of its dependencies did not succeed.
-				// See https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idneeds
-				always := false
+				// Check if the job has an "if" condition
+				hasIf := false
 				if wfJobs, _ := jobparser.Parse(r.jobMap[id].WorkflowPayload); len(wfJobs) == 1 {
 					_, wfJob := wfJobs[0].Job()
-					expr := strings.TrimSpace(strings.TrimSuffix(strings.TrimPrefix(wfJob.If.Value, "${{"), "}}"))
-					always = expr == "always()"
+					hasIf = len(wfJob.If.Value) > 0
 				}
 
-				if always {
+				if hasIf {
+					// act_runner will check the "if" condition
 					ret[id] = actions_model.StatusWaiting
 				} else {
+					// If the "if" condition is empty and not all dependent jobs completed successfully,
+					// the job should be skipped.
 					ret[id] = actions_model.StatusSkipped
 				}
 			}