Support pinning forked Go modules

get.go

@@ -622,10 +622,19 @@ func getPackage(ctx context.Context, logger *log.Logger, c installPackageConfig,
 		}
 
 		if !strings.HasSuffix(target.Module.Version, "+incompatible") {
-			fetchedDirectives, err = autoFetchDirectives(runnable, logger, target)
+			var declaredModulePath string
+			fetchedDirectives, declaredModulePath, err = autoFetchDirectives(runnable, logger, target)
 			if err != nil {
 				return err
 			}
+			if declaredModulePath != "" && declaredModulePath != target.Module.Path {
+				forkModule := target.Module
+				target.Module.Path = declaredModulePath
+				fetchedDirectives.replace = append(fetchedDirectives.replace, mod.ReplaceDirective{
+					Old: module.Version{Path: declaredModulePath},
+					New: forkModule,
+				})
+			}
 		}
 	}
 
@@ -722,10 +731,10 @@ func (d nonRequireDirectives) isEmpty() bool {
 // as the target module we want to install.
 // It's a very common case where modules mitigate faulty modules or conflicts with replace directives.
 // Since we always download single tool dependency module per tool module, we can copy its non-require statements if exists to fix this common case.
-func autoFetchDirectives(runnable runner.Runnable, logger *log.Logger, target bingo.Package) (d nonRequireDirectives, _ error) {
+func autoFetchDirectives(runnable runner.Runnable, logger *log.Logger, target bingo.Package) (d nonRequireDirectives, declaredModulePath string, err error) {
 	gopath, err := runnable.GoEnv("GOPATH")
 	if err != nil {
-		return d, errors.Wrap(err, "go env")
+		return d, "", errors.Wrap(err, "go env")
 	}
 
 	// We leverage fact that when go get runs if downloads the version we find as relevant locally
@@ -734,16 +743,19 @@ func autoFetchDirectives(runnable runner.Runnable, logger *log.Logger, target bi
 	if _, err := os.Stat(targetModFile); err != nil {
 		if os.IsNotExist(err) {
 			// Pre module package.
-			return d, nil
+			return d, "", nil
 		}
-		return d, errors.Wrapf(err, "stat target mod directory %v", targetModFile)
+		return d, "", errors.Wrapf(err, "stat target mod directory %v", targetModFile)
 	}
 
 	// Mod directory has only read permissions.
 	targetModParsed, err := mod.OpenFileForRead(targetModFile)
 	if err != nil {
-		return d, errors.Wrapf(err, "parse target mod file %v", targetModFile)
+		return d, "", errors.Wrapf(err, "parse target mod file %v", targetModFile)
 	}
+	defer errcapture.Do(&err, targetModParsed.Close, "close target mod file")
+
+	declaredModulePath, _ = targetModParsed.Module()
 
 	if semver.MustParse(targetModParsed.GoVersion()).GreaterThan(runnable.GoVersion()) {
 		logger.Printf("WARNING: Go module you are trying to install requires higher Go version (%v) than you are using (%v). Use newer Go version to install it if you encounter build errors (e.g when generics were used).\n", targetModParsed.GoVersion(), runnable.GoVersion().String())
@@ -754,9 +766,9 @@ func autoFetchDirectives(runnable runner.Runnable, logger *log.Logger, target bi
 	d.retract = targetModParsed.RetractDirectives()
 
 	if len(d.retract) > 0 && runnable.GoVersion().LessThan(version.Go116) {
-		return d, errors.Newf("target Go module is using new 'retract' directive. Use Go1.16+ to build it")
+		return d, "", errors.Newf("target Go module is using new 'retract' directive. Use Go1.16+ to build it")
 	}
-	return d, nil
+	return d, declaredModulePath, nil
 }
 
 // gobin mimics the way go install finds where to install go tool.

get_e2e_test.go

@@ -500,6 +500,10 @@ func TestGet_ModuleCases(t *testing.T) {
 	}
 
 	t.Run("benchstat: latest in case where no major version is found", func(t *testing.T) {
+		if goVersion.LessThan(semver.MustParse("v1.25")) {
+			t.Skip("latest golang.org/x/perf requires Go 1.25")
+		}
+
 		g.Clear(t)
 
 		testutil.Ok(t, os.MkdirAll(filepath.Join(g.tmpDir, "newproject"), os.ModePerm))
@@ -538,6 +542,34 @@ func TestGet_ModuleCases(t *testing.T) {
 		}
 	})
 
+	t.Run("fork with a different declared module path", func(t *testing.T) {
+		g.Clear(t)
+
+		testutil.Ok(t, os.MkdirAll(filepath.Join(g.tmpDir, "newproject"), os.ModePerm))
+		p := newTestProject(t, filepath.Join(g.tmpDir, "newproject"), filepath.Join(g.tmpDir, "testproject"), false)
+		p.assertNotChanged(t)
+
+		bingoPath := filepath.Join(g.tmpDir, bingoBin)
+		buildInitialGobin(t, bingoPath)
+
+		const forkVersion = "v1.3.1-0.20220406082449-39bc1352dc62"
+		fmt.Println(g.ExecOutput(t, p.root, bingoPath, "get", "github.com/ypresto/CompileDaemon@"+forkVersion))
+
+		expectBingoListRows(t, []row{{
+			name:       "compiledaemon",
+			binName:    "compiledaemon-" + forkVersion,
+			pkgVersion: "github.com/githubnemo/CompileDaemon@" + forkVersion,
+		}}, g.ExecOutput(t, p.root, bingoPath, "list"))
+		testutil.Equals(t, []string{"compiledaemon-" + forkVersion}, g.existingBinaries(t))
+
+		modFile, err := os.ReadFile(filepath.Join(p.root, defaultModDir, "compiledaemon.mod"))
+		testutil.Ok(t, err)
+		testutil.Equals(t, true, strings.Contains(string(modFile),
+			"replace github.com/githubnemo/CompileDaemon => github.com/ypresto/CompileDaemon "+forkVersion))
+		testutil.Equals(t, true, strings.Contains(string(modFile),
+			"require github.com/githubnemo/CompileDaemon "+forkVersion))
+	})
+
 	// Tricky cases TODO.
 
 	// Regression against https://github.com/bwplotka/bingo/issues/125