go/analysis/unitchecker: add cfg.WarnDiagnostics

This flag, set by go vet and go fix but not go test,
allows unitchecker to exit successfully even when
it prints diagnostics, allowing the go command to
cache its output.

The legacy behavior remains in place for other
build systems.

Updates golang/go#71859

Change-Id: I4e025ef896fe191795e6bc4f284ab739dc3b6abc
Reviewed-on: https://go-review.googlesource.com/c/tools/+/703995
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
Auto-Submit: Alan Donovan <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>

Author: adonovan

go/analysis/unitchecker/unitchecker.go

@@ -74,7 +74,8 @@ type Config struct {
 	VetxOnly                  bool              // run analysis only for facts, not diagnostics
 	VetxOutput                string            // where to write file of fact information
 	Stdout                    string            // write stdout (e.g. JSON, unified diff) to this file
-	SucceedOnTypecheckFailure bool
+	SucceedOnTypecheckFailure bool              // obsolete awful hack; see #18395 and below
+	WarnDiagnostics           bool              // printing diagnostics should not cause a non-zero exit
 }
 
 // Main is the main function of a vet-like analysis tool that must be
@@ -162,7 +163,7 @@ func Run(configFile string, analyzers []*analysis.Analyzer) {
 
 	// In VetxOnly mode, the analysis is run only for facts.
 	if !cfg.VetxOnly {
-		code = processResults(fset, cfg.ID, results)
+		code = processResults(fset, cfg.ID, results, cfg.WarnDiagnostics)
 	}
 
 	os.Exit(code)
@@ -186,7 +187,7 @@ func readConfig(filename string) (*Config, error) {
 	return cfg, nil
 }
 
-func processResults(fset *token.FileSet, id string, results []result) (exit int) {
+func processResults(fset *token.FileSet, id string, results []result, warnDiagnostics bool) (exit int) {
 	if analysisflags.Fix {
 		// Don't print the diagnostics,
 		// but apply all fixes from the root actions.
@@ -235,7 +236,9 @@ func processResults(fset *token.FileSet, id string, results []result) (exit int)
 		for _, res := range results {
 			for _, diag := range res.diagnostics {
 				analysisflags.PrintPlain(os.Stderr, fset, analysisflags.Context, diag)
-				exit = 1
+				if !warnDiagnostics {
+					exit = 1
+				}
 			}
 		}
 	}