Go: Deal with incorrect toolchain versions

go/extractor/cli/go-autobuilder/go-autobuilder.go

@@ -475,7 +475,7 @@ func installDependencies(workspace project.GoWorkspace) {
 	} else {
 		if workspace.Modules == nil {
 			project.InitGoModForLegacyProject(workspace.BaseDir)
-			workspace.Modules = project.LoadGoModules([]string{filepath.Join(workspace.BaseDir, "go.mod")})
+			workspace.Modules = project.LoadGoModules(true, []string{filepath.Join(workspace.BaseDir, "go.mod")})
 		}
 
 		// get dependencies for all modules

go/extractor/diagnostics/diagnostics.go

@@ -508,3 +508,18 @@ func EmitExtractionFailedForProjects(path []string) {
 		noLocation,
 	)
 }
+
+func EmitInvalidToolchainVersion(goModPath string, version string) {
+	emitDiagnostic(
+		"go/autobuilder/invalid-go-toolchain-version",
+		fmt.Sprintf("`%s` is not a valid Go toolchain version", version),
+		strings.Join([]string{
+			"As of Go 1.21, toolchain versions [must use the 1.N.P syntax](https://tip.golang.org/doc/toolchain#version).",
+			fmt.Sprintf("`%s` in `%s` does not match this syntax and there is no additional `toolchain` directive, which may cause some `go` commands to fail.", version, goModPath),
+		},
+			"\n\n"),
+		severityWarning,
+		fullVisibility,
+		&locationStruct{File: goModPath},
+	)
+}

go/extractor/project/project.go

@@ -176,10 +176,13 @@ func findGoModFiles(root string) []string {
 	return util.FindAllFilesWithName(root, "go.mod", "vendor")
 }
 
+// A regular expression for the Go toolchain version syntax.
+var toolchainVersionRe *regexp.Regexp = regexp.MustCompile(`(?m)^([0-9]+\.[0-9]+\.[0-9]+)$`)
+
 // Given a list of `go.mod` file paths, try to parse them all. The resulting array of `GoModule` objects
 // will be the same length as the input array and the objects will contain at least the `go.mod` path.
 // If parsing the corresponding file is successful, then the parsed contents will also be available.
-func LoadGoModules(goModFilePaths []string) []*GoModule {
+func LoadGoModules(emitDiagnostics bool, goModFilePaths []string) []*GoModule {
 	results := make([]*GoModule, len(goModFilePaths))
 
 	for i, goModFilePath := range goModFilePaths {
@@ -201,6 +204,15 @@ func LoadGoModules(goModFilePaths []string) []*GoModule {
 		}
 
 		results[i].Module = modFile
+
+		// If this `go.mod` file specifies a Go language version, that version is `1.21` or greater, and
+		// there is no `toolchain` directive, check that it is a valid Go toolchain version. Otherwise,
+		// `go` commands which try to download the right version of the Go toolchain will fail. We detect
+		// this situation and emit a diagnostic.
+		if modFile.Toolchain == nil && modFile.Go != nil &&
+			!toolchainVersionRe.Match([]byte(modFile.Go.Version)) && semver.Compare("v"+modFile.Go.Version, "v1.21.0") >= 0 {
+			diagnostics.EmitInvalidToolchainVersion(goModFilePath, modFile.Go.Version)
+		}
 	}
 
 	return results
@@ -209,7 +221,7 @@ func LoadGoModules(goModFilePaths []string) []*GoModule {
 // Given a path to a `go.work` file, this function attempts to parse the `go.work` file. If unsuccessful,
 // we attempt to discover `go.mod` files within subdirectories of the directory containing the `go.work`
 // file ourselves.
-func discoverWorkspace(workFilePath string) GoWorkspace {
+func discoverWorkspace(emitDiagnostics bool, workFilePath string) GoWorkspace {
 	log.Printf("Loading %s...\n", workFilePath)
 	baseDir := filepath.Dir(workFilePath)
 	workFileSrc, err := os.ReadFile(workFilePath)
@@ -223,7 +235,7 @@ func discoverWorkspace(workFilePath string) GoWorkspace {
 
 		return GoWorkspace{
 			BaseDir: baseDir,
-			Modules: LoadGoModules(goModFilePaths),
+			Modules: LoadGoModules(emitDiagnostics, goModFilePaths),
 			DepMode: GoGetWithModules,
 			ModMode: getModMode(GoGetWithModules, baseDir),
 		}
@@ -240,7 +252,7 @@ func discoverWorkspace(workFilePath string) GoWorkspace {
 
 		return GoWorkspace{
 			BaseDir: baseDir,
-			Modules: LoadGoModules(goModFilePaths),
+			Modules: LoadGoModules(emitDiagnostics, goModFilePaths),
 			DepMode: GoGetWithModules,
 			ModMode: getModMode(GoGetWithModules, baseDir),
 		}
@@ -263,7 +275,7 @@ func discoverWorkspace(workFilePath string) GoWorkspace {
 	return GoWorkspace{
 		BaseDir:       baseDir,
 		WorkspaceFile: workFile,
-		Modules:       LoadGoModules(goModFilePaths),
+		Modules:       LoadGoModules(emitDiagnostics, goModFilePaths),
 		DepMode:       GoGetWithModules,
 		ModMode:       ModReadonly, // Workspaces only support "readonly"
 	}
@@ -286,7 +298,7 @@ func discoverWorkspaces(emitDiagnostics bool) []GoWorkspace {
 		for i, goModFile := range goModFiles {
 			results[i] = GoWorkspace{
 				BaseDir: filepath.Dir(goModFile),
-				Modules: LoadGoModules([]string{goModFile}),
+				Modules: LoadGoModules(emitDiagnostics, []string{goModFile}),
 				DepMode: GoGetWithModules,
 				ModMode: getModMode(GoGetWithModules, filepath.Dir(goModFile)),
 			}
@@ -303,7 +315,7 @@ func discoverWorkspaces(emitDiagnostics bool) []GoWorkspace {
 
 		results := make([]GoWorkspace, len(goWorkFiles))
 		for i, workFilePath := range goWorkFiles {
-			results[i] = discoverWorkspace(workFilePath)
+			results[i] = discoverWorkspace(emitDiagnostics, workFilePath)
 		}
 
 		// Add all stray `go.mod` files (i.e. those not referenced by `go.work` files)
@@ -335,7 +347,7 @@ func discoverWorkspaces(emitDiagnostics bool) []GoWorkspace {
 				log.Printf("Module %s is not referenced by any go.work file; adding it separately.\n", goModFile)
 				results = append(results, GoWorkspace{
 					BaseDir: filepath.Dir(goModFile),
-					Modules: LoadGoModules([]string{goModFile}),
+					Modules: LoadGoModules(emitDiagnostics, []string{goModFile}),
 					DepMode: GoGetWithModules,
 					ModMode: getModMode(GoGetWithModules, filepath.Dir(goModFile)),
 				})