feat(linter): add file/line to findings; downgrade extends missing-script to warning

Every finding now carries the source file and exact line number of the job
key in its YAML file. Format: [ERROR] job "name" (file.yml:12): message.

Pipeline-level findings (workflow rules, no stages) reference p.SourceFile.
Cross-file include jobs (local, project, component) carry the include source
as their File, set via Pipeline.SetJobOrigin after each ParseBytes call in
the resolver.

Line numbers come from the yaml.Node key node (exact job-name line) in a
new document-level first pass in ParseBytes, replacing the previous
map[string]yaml.Node approach which only gave value-node lines.

Also: jobs that declare extends: but have no script after resolution now
emit WARNING instead of ERROR. The script may come from a base in a remote
include that was not fetched (no token, offline), making the error a false
positive in common project setups.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/linter/linter.go

@@ -17,12 +17,25 @@ const (
 type Finding struct {
 	Severity Severity
 	Job      string // empty for pipeline-level findings
+	File     string // source file where the finding originates
+	Line     int    // line number in File (0 = unknown)
 	Message  string
 }
 
 func (f Finding) String() string {
+	loc := ""
+	if f.File != "" {
+		if f.Line > 0 {
+			loc = fmt.Sprintf(" (%s:%d)", f.File, f.Line)
+		} else {
+			loc = fmt.Sprintf(" (%s)", f.File)
+		}
+	}
 	if f.Job != "" {
-		return fmt.Sprintf("[%s] job %q: %s", f.Severity, f.Job, f.Message)
+		return fmt.Sprintf("[%s] job %q%s: %s", f.Severity, f.Job, loc, f.Message)
+	}
+	if loc != "" {
+		return fmt.Sprintf("[%s]%s: %s", f.Severity, loc, f.Message)
 	}
 	return fmt.Sprintf("[%s] %s", f.Severity, f.Message)
 }
@@ -43,6 +56,7 @@ func checkStages(p *model.Pipeline) []Finding {
 	if len(p.Stages) == 0 {
 		findings = append(findings, Finding{
 			Severity: Warning,
+			File:     p.SourceFile,
 			Message:  "no stages defined; GitLab will use default stages (build, test, deploy)",
 		})
 	}
@@ -58,6 +72,7 @@ func checkWorkflow(p *model.Pipeline) []Finding {
 		if rule.When != "" && !validWorkflowRuleWhen[rule.When] {
 			findings = append(findings, Finding{
 				Severity: Error,
+				File:     p.SourceFile,
 				Message:  fmt.Sprintf("workflow.rules[%d].when has invalid value %q; valid: always, never", i, rule.When),
 			})
 		}
@@ -88,10 +103,16 @@ func checkJob(name string, job model.Job, stageSet map[string]bool) []Finding {
 
 	// After extends resolution, a job with no script/run is an error.
 	// Exceptions: trigger jobs, pages jobs (use pages: keyword), and template jobs.
+	// When the job has extends:, the script may come from a base that couldn't be
+	// fetched (e.g. a remote include without a token), so downgrade to warning.
 	hasScript := scriptNonEmpty(job.Script) || job.Run != nil
 	if !isTemplate && !isTrigger && job.Pages == nil && !hasScript {
+		sev := Error
+		if job.Extends != nil {
+			sev = Warning
+		}
 		findings = append(findings, Finding{
-			Severity: Error,
+			Severity: sev,
 			Job:      name,
 			Message:  "missing required field 'script' (or 'run')",
 		})
@@ -137,6 +158,13 @@ func checkJob(name string, job model.Job, stageSet map[string]bool) []Finding {
 
 	findings = append(findings, checkJobKeywords(name, job)...)
 
+	// Attach source location to every job-scoped finding collected above.
+	for i := range findings {
+		if findings[i].Job != "" && findings[i].File == "" {
+			findings[i].File = job.File
+			findings[i].Line = job.Line
+		}
+	}
 	return findings
 }