[release-branch.go1.16] cmd/go: clarify errors for commands run outside a module

The new error message tells the user what was wrong (no go.mod found)
and directs them to 'go help modules', which links to tutorials.

Includes test fix from CL 298794
Fixes #44746

Change-Id: I98f31fec4a8757eb1792b45491519da4c552cb0f
Reviewed-on: https://go-review.googlesource.com/c/go/+/298650
Trust: Jay Conrod <[email protected]>
Run-TryBot: Jay Conrod <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>
(cherry picked from commit b87e9b9)
Reviewed-on: https://go-review.googlesource.com/c/go/+/298929

Author: Jay Conrod

src/cmd/go/internal/modget/query.go

@@ -186,7 +186,7 @@ func (q *query) validate() error {
 	if q.pattern == "all" {
 		// If there is no main module, "all" is not meaningful.
 		if !modload.HasModRoot() {
-			return fmt.Errorf(`cannot match "all": working directory is not part of a module`)
+			return fmt.Errorf(`cannot match "all": %v`, modload.ErrNoModRoot)
 		}
 		if !versionOkForMainModule(q.version) {
 			// TODO(bcmills): "all@none" seems like a totally reasonable way to

src/cmd/go/internal/modload/import.go

@@ -51,7 +51,7 @@ func (e *ImportMissingError) Error() string {
 		if e.isStd {
 			return fmt.Sprintf("package %s is not in GOROOT (%s)", e.Path, filepath.Join(cfg.GOROOT, "src", e.Path))
 		}
-		if e.QueryErr != nil {
+		if e.QueryErr != nil && e.QueryErr != ErrNoModRoot {
 			return fmt.Sprintf("cannot find module providing package %s: %v", e.Path, e.QueryErr)
 		}
 		if cfg.BuildMod == "mod" || (cfg.BuildMod == "readonly" && allowMissingModuleImports) {
@@ -66,13 +66,11 @@ func (e *ImportMissingError) Error() string {
 			return fmt.Sprintf("module %s provides package %s and is replaced but not required; to add it:\n\tgo get %s", e.replaced.Path, e.Path, suggestArg)
 		}
 
-		suggestion := ""
-		if !HasModRoot() {
-			suggestion = ": working directory is not part of a module"
-		} else {
-			suggestion = fmt.Sprintf("; to add it:\n\tgo get %s", e.Path)
+		message := fmt.Sprintf("no required module provides package %s", e.Path)
+		if e.QueryErr != nil {
+			return fmt.Sprintf("%s: %v", message, e.QueryErr)
 		}
-		return fmt.Sprintf("no required module provides package %s%s", e.Path, suggestion)
+		return fmt.Sprintf("%s; to add it:\n\tgo get %s", message, e.Path)
 	}
 
 	if e.newMissingVersion != "" {
@@ -318,7 +316,11 @@ func importFromBuildList(ctx context.Context, path string, buildList []module.Ve
 		return mods[0], dirs[0], nil
 	}
 
-	return module.Version{}, "", &ImportMissingError{Path: path, isStd: pathIsStd}
+	var queryErr error
+	if !HasModRoot() {
+		queryErr = ErrNoModRoot
+	}
+	return module.Version{}, "", &ImportMissingError{Path: path, QueryErr: queryErr, isStd: pathIsStd}
 }
 
 // queryImport attempts to locate a module that can be added to the current

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

@@ -177,7 +177,7 @@ func Init() {
 				base.Fatalf("go: cannot find main module, but -modfile was set.\n\t-modfile cannot be used to set the module root directory.")
 			}
 			if RootMode == NeedRoot {
-				base.Fatalf("go: cannot find main module; see 'go help modules'")
+				base.Fatalf("go: %v", ErrNoModRoot)
 			}
 			if !mustUseModules {
 				// GO111MODULE is 'auto', and we can't find a module root.
@@ -338,9 +338,11 @@ func die() {
 		}
 		base.Fatalf("go: cannot find main module, but found %s in %s\n\tto create a module there, run:\n\t%sgo mod init", name, dir, cdCmd)
 	}
-	base.Fatalf("go: cannot find main module; see 'go help modules'")
+	base.Fatalf("go: %v", ErrNoModRoot)
 }
 
+var ErrNoModRoot = errors.New("go.mod file not found in current directory or any parent directory; see 'go help modules'")
+
 // LoadModFile sets Target and, if there is a main module, parses the initial
 // build list from its go.mod file.
 //

src/cmd/go/internal/modload/list.go

@@ -73,7 +73,7 @@ func listModules(ctx context.Context, args []string, listVersions, listRetracted
 			base.Fatalf("go: cannot use relative path %s to specify module", arg)
 		}
 		if !HasModRoot() && (arg == "all" || strings.Contains(arg, "...")) {
-			base.Fatalf("go: cannot match %q: working directory is not part of a module", arg)
+			base.Fatalf("go: cannot match %q: %v", arg, ErrNoModRoot)
 		}
 		if i := strings.Index(arg, "@"); i >= 0 {
 			path := arg[:i]

src/cmd/go/internal/run/run.go

@@ -96,28 +96,12 @@ func runRun(ctx context.Context, cmd *base.Command, args []string) {
 		base.Fatalf("go run: no go files listed")
 	}
 	cmdArgs := args[i:]
-	if p.Error != nil {
-		base.Fatalf("%s", p.Error)
-	}
+	load.CheckPackageErrors([]*load.Package{p})
 
-	p.Internal.OmitDebug = true
-	if len(p.DepsErrors) > 0 {
-		// Since these are errors in dependencies,
-		// the same error might show up multiple times,
-		// once in each package that depends on it.
-		// Only print each once.
-		printed := map[*load.PackageError]bool{}
-		for _, err := range p.DepsErrors {
-			if !printed[err] {
-				printed[err] = true
-				base.Errorf("%s", err)
-			}
-		}
-	}
-	base.ExitIfErrors()
 	if p.Name != "main" {
 		base.Fatalf("go run: cannot run non-main package")
 	}
+	p.Internal.OmitDebug = true
 	p.Target = "" // must build - not up to date
 	if p.Internal.CmdlineFiles {
 		//set executable name if go file is given as cmd-argument

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

@@ -18,7 +18,7 @@ stdout '^m$'
 # Test that we ignore directories when trying to find alternate config files.
 cd $WORK/gopkgdir/x
 ! go list .
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 ! stderr 'Gopkg.lock'
 
 -- $WORK/test/Gopkg.lock --

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

@@ -49,7 +49,7 @@ rm go.mod
 # Test that we ignore directories when trying to find go.mod.
 cd $WORK/gomoddir
 ! go list .
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 [!symlink] stop
 

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

@@ -59,9 +59,9 @@ rm $GOPATH/bin
 env GO111MODULE=on
 go mod download rsc.io/[email protected]
 ! go install $GOPATH/pkg/mod/rsc.io/[email protected]
-stderr '^go: cannot find main module; see ''go help modules''$'
+stderr '^go: go\.mod file not found in current directory or any parent directory; see ''go help modules''$'
 ! go install ../pkg/mod/rsc.io/[email protected]
-stderr '^go: cannot find main module; see ''go help modules''$'
+stderr '^go: go\.mod file not found in current directory or any parent directory; see ''go help modules''$'
 mkdir tmp
 cd tmp
 go mod init tmp

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

@@ -12,13 +12,13 @@ stdout 'NUL|/dev/null'
 # 'go list' without arguments implicitly operates on the current directory,
 # which is not in a module.
 ! go list
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 go list -m
 stdout '^command-line-arguments$'
 # 'go list' in the working directory should fail even if there is a a 'package
 # main' present: without a main module, we do not know its package path.
 ! go list ./needmod
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go list all' lists the transitive import graph of the main module,
 # which is empty if there is no main module.
@@ -41,7 +41,7 @@ stdout 'command-line-arguments'
 
 # 'go list' on a package from a module should fail.
 ! go list example.com/printversion
-stderr '^no required module provides package example.com/printversion: working directory is not part of a module$'
+stderr '^no required module provides package example.com/printversion: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 
 # 'go list -m' with an explicit version should resolve that version.
@@ -54,19 +54,19 @@ stdout 'v1.0.0\s+v1.0.1\s+v1.1.0'
 
 # 'go list -m all' should fail. "all" is not meaningful outside of a module.
 ! go list -m all
-stderr 'go: cannot match "all": working directory is not part of a module'
+stderr 'go: cannot match "all": go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go list -m <mods> all' should also fail.
 ! go list -m example.com/[email protected] all
-stderr 'go: cannot match "all": working directory is not part of a module'
+stderr 'go: cannot match "all": go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 ! stdout 'example.com/version'
 
 # 'go list -m' with wildcards should fail. Wildcards match modules in the
 # build list, so they aren't meaningful outside a module.
 ! go list -m ...
-stderr 'go: cannot match "...": working directory is not part of a module'
+stderr 'go: cannot match "...": go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 ! go list -m rsc.io/quote/...
-stderr 'go: cannot match "rsc.io/quote/...": working directory is not part of a module'
+stderr 'go: cannot match "rsc.io/quote/...": go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 
 # 'go clean' should skip the current directory if it isn't in a module.
@@ -76,20 +76,20 @@ go clean -n
 
 # 'go mod graph' should fail, since there's no module graph.
 ! go mod graph
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go mod why' should fail, since there is no main module to depend on anything.
 ! go mod why -m example.com/version
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go mod edit', 'go mod tidy', and 'go mod fmt' should fail:
 # there is no go.mod file to edit.
 ! go mod tidy
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 ! go mod edit -fmt
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 ! go mod edit -require example.com/[email protected]
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 
 # 'go mod download' without arguments should report an error.
@@ -104,33 +104,33 @@ exists $GOPATH/pkg/mod/cache/download/example.com/printversion/@v/v1.0.0.zip
 
 # 'go mod download all' should fail. "all" is not meaningful outside of a module.
 ! go mod download all
-stderr 'go: cannot match "all": working directory is not part of a module'
+stderr 'go: cannot match "all": go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 
 # 'go mod vendor' should fail: it starts by clearing the existing vendor
 # directory, and we don't know where that is.
 ! go mod vendor
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 
 # 'go mod verify' should fail: we have no modules to verify.
 ! go mod verify
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 
 # 'go get' without arguments implicitly operates on the main module, and thus
 # should fail.
 ! go get
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 ! go get -u
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 ! go get -u ./needmod
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go get -u all' upgrades the transitive import graph of the main module,
 # which is empty.
 ! go get -u all
-stderr 'go get: cannot match "all": working directory is not part of a module'
+stderr '^go get: cannot match "all": go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go get' should check the proposed module graph for consistency,
 # even though we won't write it anywhere.
@@ -147,16 +147,16 @@ exists $GOPATH/pkg/mod/example.com/[email protected]
 # 'go build' without arguments implicitly operates on the current directory, and should fail.
 cd needmod
 ! go build
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 cd ..
 
 # 'go build' of a non-module directory should fail too.
 ! go build ./needmod
-stderr 'cannot find main module'
+stderr '^go: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go build' of source files should fail if they import anything outside std.
 ! go build -n ./needmod/needmod.go
-stderr '^needmod[/\\]needmod.go:10:2: no required module provides package example.com/version: working directory is not part of a module$'
+stderr '^needmod[/\\]needmod.go:10:2: no required module provides package example.com/version: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go build' of source files should succeed if they do not import anything outside std.
 go build -n -o ignore ./stdonly/stdonly.go
@@ -179,7 +179,7 @@ go doc fmt
 
 # 'go doc' should fail for a package path outside a module.
 ! go doc example.com/version
-stderr 'doc: no required module provides package example.com/version: working directory is not part of a module'
+stderr 'doc: no required module provides package example.com/version: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go install' with a version should succeed if all constraints are met.
 # See mod_install_pkg_version.
@@ -194,7 +194,7 @@ stderr '^go install: version is required when current directory is not in a modu
 # 'go install' should fail if a source file imports a package that must be
 # resolved to a module.
 ! go install ./needmod/needmod.go
-stderr 'needmod[/\\]needmod.go:10:2: no required module provides package example.com/version: working directory is not part of a module'
+stderr 'needmod[/\\]needmod.go:10:2: no required module provides package example.com/version: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go install' should succeed with a package in GOROOT.
 go install cmd/addr2line
@@ -206,12 +206,12 @@ stderr 'can only use path@version syntax with'
 
 # 'go run' should fail if a package argument must be resolved to a module.
 ! go run example.com/printversion
-stderr '^no required module provides package example.com/printversion: working directory is not part of a module$'
+stderr '^no required module provides package example.com/printversion: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 # 'go run' should fail if a source file imports a package that must be
 # resolved to a module.
 ! go run ./needmod/needmod.go
-stderr '^needmod[/\\]needmod.go:10:2: no required module provides package example.com/version: working directory is not part of a module$'
+stderr '^needmod[/\\]needmod.go:10:2: no required module provides package example.com/version: go.mod file not found in current directory or any parent directory; see ''go help modules''$'
 
 
 # 'go fmt' should be able to format files outside of a module.

src/go/build/build_test.go

@@ -612,7 +612,7 @@ func TestImportPackageOutsideModule(t *testing.T) {
 	ctxt.GOPATH = gopath
 	ctxt.Dir = filepath.Join(gopath, "src/example.com/p")
 
-	want := "working directory is not part of a module"
+	want := "go.mod file not found in current directory or any parent directory"
 	if _, err := ctxt.Import("example.com/p", gopath, FindOnly); err == nil {
 		t.Fatal("importing package when no go.mod is present succeeded unexpectedly")
 	} else if errStr := err.Error(); !strings.Contains(errStr, want) {