fix: return early in DiscoverRunner to avoid unnecessary env checks

Stop iterating through all runner factories after the first matching
runner is found. Previously, DiscoverRunner would check every registered
runner (GitHub, GitLab, Azure, Jenkins, CircleCI, Dagger, TeamCity,
Tekton) even after finding a match. Some runners perform expensive
operations in CheckEnv() — opening k8s config files (Tekton) or making
API calls (GitHub) — making attestation init slower as more runners are
added.

Fixes #2834

Author: waveywaves

pkg/attestation/crafter/runner.go

@@ -114,35 +114,19 @@ func NewRunner(t schemaapi.CraftingSchema_Runner_RunnerType, authToken string, l
 
 // DiscoverRunner the runner environment
 // This method does a simple check to see which runner is available in the environment
-// by iterating over the different runners and performing duck-typing checks
-// If more than one runner is detected, we default to generic since its an incongruent result
+// by iterating over the different runners and performing duck-typing checks.
+// It returns the first matching runner immediately to avoid unnecessary environment
+// checks (e.g., opening k8s config files, making API calls) from other runners.
 func DiscoverRunner(authToken string, logger zerolog.Logger) SupportedRunner {
-	detected := []SupportedRunner{}
-
-	// Create all runners and check their environment
-	for _, factory := range RunnerFactories {
+	for runnerType, factory := range RunnerFactories {
 		r := factory(authToken, &logger)
 		if r.CheckEnv() {
-			detected = append(detected, r)
-		}
-	}
-
-	// if we don't detect any runner or more than one, we default to generic
-	if len(detected) == 0 {
-		return runners.NewGeneric()
-	}
-
-	if len(detected) > 1 {
-		var detectedStr []string
-		for _, d := range detected {
-			detectedStr = append(detectedStr, d.ID().String())
+			logger.Debug().Str("runner", runnerType.String()).Msg("runner detected")
+			return r
 		}
-
-		logger.Warn().Strs("detected", detectedStr).Msg("multiple runners detected, incongruent environment")
-		return runners.NewGeneric()
 	}
 
-	return detected[0]
+	return runners.NewGeneric()
 }
 
 func DiscoverAndEnforceRunner(enforcedRunnerType schemaapi.CraftingSchema_Runner_RunnerType, dryRun bool, authToken string, logger zerolog.Logger) (SupportedRunner, error) {