cmd/go: return more errors from ReadModFile, loadModFile

Return more errors instead of base.Fatalf, so we can handle them
in the callers.

For #57001.

Change-Id: If3e63d3f64188148f5d750991f9cb1175790d89d
Reviewed-on: https://go-review.googlesource.com/c/go/+/499983
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

src/cmd/go/internal/gover/toolchain.go

@@ -60,6 +60,7 @@ var Startup struct {
 type TooNewError struct {
 	What      string
 	GoVersion string
+	Toolchain string // for callers if they want to use it, but not printed
 }
 
 func (e *TooNewError) Error() string {

src/cmd/go/internal/modload/buildlist.go

@@ -541,7 +541,10 @@ func (mg *ModuleGraph) allRootsSelected() bool {
 // LoadModGraph need only be called if LoadPackages is not,
 // typically in commands that care about modules but no particular package.
 func LoadModGraph(ctx context.Context, goVersion string) (*ModuleGraph, error) {
-	rs := LoadModFile(ctx)
+	rs, err := loadModFile(ctx, nil)
+	if err != nil {
+		return nil, err
+	}
 
 	if goVersion != "" {
 		v, _ := rs.rootSelected("go")

src/cmd/go/internal/modload/init.go

@@ -731,12 +731,16 @@ func UpdateWorkFile(wf *modfile.WorkFile) {
 // it for global consistency. Most callers outside of the modload package should
 // use LoadModGraph instead.
 func LoadModFile(ctx context.Context) *Requirements {
-	return loadModFile(ctx, nil)
+	rs, err := loadModFile(ctx, nil)
+	if err != nil {
+		base.Fatal(err)
+	}
+	return rs
 }
 
-func loadModFile(ctx context.Context, opts *PackageOpts) *Requirements {
+func loadModFile(ctx context.Context, opts *PackageOpts) (*Requirements, error) {
 	if requirements != nil {
-		return requirements
+		return requirements, nil
 	}
 
 	Init()
@@ -745,7 +749,7 @@ func loadModFile(ctx context.Context, opts *PackageOpts) *Requirements {
 		var err error
 		workFile, modRoots, err = loadWorkFile(workFilePath)
 		if err != nil {
-			base.Fatalf("reading go.work: %v", err)
+			return nil, fmt.Errorf("reading go.work: %w", err)
 		}
 		for _, modRoot := range modRoots {
 			sumFile := strings.TrimSuffix(modFilePath(modRoot), ".mod") + ".sum"
@@ -796,22 +800,23 @@ func loadModFile(ctx context.Context, opts *PackageOpts) *Requirements {
 			// with no dependencies.
 			requirements.initVendor(nil)
 		}
-		return requirements
+		return requirements, nil
 	}
 
 	var modFiles []*modfile.File
 	var mainModules []module.Version
 	var indices []*modFileIndex
+	var errs []error
 	for _, modroot := range modRoots {
 		gomod := modFilePath(modroot)
 		var fixed bool
 		data, f, err := ReadModFile(gomod, fixVersion(ctx, &fixed))
 		if err != nil {
 			if inWorkspaceMode() {
-				base.Fatalf("go: cannot load module %s listed in go.work file: %v", base.ShortPath(gomod), err)
-			} else {
-				base.Fatalf("go: %v", err)
+				err = fmt.Errorf("cannot load module %s listed in go.work file: %w", base.ShortPath(gomod), err)
 			}
+			errs = append(errs, err)
+			continue
 		}
 
 		modFiles = append(modFiles, f)
@@ -823,9 +828,12 @@ func loadModFile(ctx context.Context, opts *PackageOpts) *Requirements {
 			if pathErr, ok := err.(*module.InvalidPathError); ok {
 				pathErr.Kind = "module"
 			}
-			base.Fatalf("go: %v", err)
+			errs = append(errs, err)
 		}
 	}
+	if len(errs) > 0 {
+		return nil, errors.Join(errs...)
+	}
 
 	MainModules = makeMainModules(mainModules, modRoots, modFiles, indices, workFile)
 	setDefaultBuildMod() // possibly enable automatic vendoring
@@ -835,7 +843,7 @@ func loadModFile(ctx context.Context, opts *PackageOpts) *Requirements {
 		// We don't need to do anything for vendor or update the mod file so
 		// return early.
 		requirements = rs
-		return rs
+		return rs, nil
 	}
 
 	mainModule := MainModules.mustGetSingleMainModule()
@@ -855,7 +863,7 @@ func loadModFile(ctx context.Context, opts *PackageOpts) *Requirements {
 		var err error
 		rs, err = updateRoots(ctx, rs.direct, rs, nil, nil, false)
 		if err != nil {
-			base.Fatal(err)
+			return nil, err
 		}
 	}
 
@@ -880,7 +888,7 @@ func loadModFile(ctx context.Context, opts *PackageOpts) *Requirements {
 				var err error
 				rs, err = convertPruning(ctx, rs, pruned)
 				if err != nil {
-					base.Fatal(err)
+					return nil, err
 				}
 			}
 		} else {
@@ -889,7 +897,7 @@ func loadModFile(ctx context.Context, opts *PackageOpts) *Requirements {
 	}
 
 	requirements = rs
-	return requirements
+	return requirements, nil
 }
 
 // CreateModFile initializes a new module by creating a go.mod file.

src/cmd/go/internal/modload/load.go

@@ -341,7 +341,10 @@ func LoadPackages(ctx context.Context, opts PackageOpts, patterns ...string) (ma
 		}
 	}
 
-	initialRS := loadModFile(ctx, &opts)
+	initialRS, err := loadModFile(ctx, &opts)
+	if err != nil {
+		base.Fatal(err)
+	}
 
 	ld := loadFromRoots(ctx, loaderParams{
 		PackageOpts:  opts,

src/cmd/go/internal/modload/modfile.go

@@ -30,6 +30,7 @@ import (
 // ReadModFile reads and parses the mod file at gomod. ReadModFile properly applies the
 // overlay, locks the file while reading, and applies fix, if applicable.
 func ReadModFile(gomod string, fix modfile.VersionFixer) (data []byte, f *modfile.File, err error) {
+	gomod = base.ShortPath(gomod) // use short path in any errors
 	if gomodActual, ok := fsys.OverlayPath(gomod); ok {
 		// Don't lock go.mod if it's part of the overlay.
 		// On Plan 9, locking requires chmod, and we don't want to modify any file
@@ -45,14 +46,18 @@ func ReadModFile(gomod string, fix modfile.VersionFixer) (data []byte, f *modfil
 	f, err = modfile.Parse(gomod, data, fix)
 	if err != nil {
 		// Errors returned by modfile.Parse begin with file:line.
-		return nil, nil, fmt.Errorf("errors parsing go.mod:\n%s\n", err)
+		return nil, nil, fmt.Errorf("errors parsing %s:\n%w", gomod, err)
 	}
-	if f.Go != nil && gover.Compare(f.Go.Version, gover.Local()) > 0 && cfg.CmdName != "mod edit" {
-		base.Fatalf("go: %v", &gover.TooNewError{What: base.ShortPath(gomod), GoVersion: f.Go.Version})
+	if f.Go != nil && gover.Compare(f.Go.Version, gover.Local()) > 0 {
+		toolchain := ""
+		if f.Toolchain != nil {
+			toolchain = f.Toolchain.Name
+		}
+		return nil, nil, &gover.TooNewError{What: gomod, GoVersion: f.Go.Version, Toolchain: toolchain}
 	}
 	if f.Module == nil {
 		// No module declaration. Must add module path.
-		return nil, nil, errors.New("no module declaration in go.mod. To specify the module path:\n\tgo mod edit -module=example.com/mod")
+		return nil, nil, fmt.Errorf("error reading %s: missing module declaration. To specify the module path:\n\tgo mod edit -module=example.com/mod", gomod)
 	}
 
 	return data, f, err

src/cmd/go/testdata/script/mod_goline_too_new.txt

@@ -8,7 +8,7 @@ stderr '^go: go.mod requires go >= 1.99999 \(running go 1\..+\)$'
 # go.mod referenced from go.work too new
 cp go.work.old go.work
 ! go build .
-stderr '^go: go.mod requires go >= 1.99999 \(running go 1\..+\)$'
+stderr '^go: cannot load module go.mod listed in go.work file: go.mod requires go >= 1.99999 \(running go 1\..+\)$'
 
 # go.work too new
 cp go.work.new go.work

src/cmd/go/testdata/script/mod_invalid_path.txt

@@ -3,7 +3,7 @@
 # Test that go list fails on a go.mod with no module declaration.
 cd $WORK/gopath/src/mod
 ! go list .
-stderr '^go: no module declaration in go.mod. To specify the module path:\n\tgo mod edit -module=example.com/mod$'
+stderr '^go: error reading go.mod: missing module declaration. To specify the module path:\n\tgo mod edit -module=example.com/mod$'
 
 # Test that go mod init in GOPATH doesn't add a module declaration
 # with a path that can't possibly be a module path, because

src/cmd/go/testdata/script/mod_invalid_version.txt

@@ -50,7 +50,7 @@ cd outside
 stderr 'go: example.com@v0.0.0 \(replaced by \./\.\.\): parsing ..[/\\]go.mod: '$WORK'[/\\]gopath[/\\]src[/\\]go.mod:5: require golang.org/x/text: version "v2.1.1-0.20170915032832-14c0d48ead0c" invalid: should be v0 or v1, not v2'
 cd ..
 ! go list -m golang.org/x/text
-stderr $WORK'[/\\]gopath[/\\]src[/\\]go.mod:5: require golang.org/x/text: version "v2.1.1-0.20170915032832-14c0d48ead0c" invalid: should be v0 or v1, not v2'
+stderr '^go.mod:5: require golang.org/x/text: version "v2.1.1-0.20170915032832-14c0d48ead0c" invalid: should be v0 or v1, not v2'
 
 # A pseudo-version with fewer than 12 digits of SHA-1 prefix is invalid.
 cp go.mod.orig go.mod