cmd/go/internal/modload: improve ErrNoModRoot error text

Before this change, in several cases where HasModRoot() returned false,
we'd return ErrNoModRoot. ErrNoModRoot would say that there was no
go.mod file but would not mention workspaces. With this change,
ErrNoModRoot will return error text that's different if we're in a
workspace, saying that there are no modules in the workspace.

Fixes #54419

Change-Id: I77c94d0011947bf8e33c066416ab3762502fd2e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/660675
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 1ffe5052fb359026a9c903d1c1c54204fab5c485..41b3b9df1ba20c394e10872420186b212a9238b4 100644 (file)
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -610,7 +610,7 @@ func inWorkspaceMode() bool {
        return workFilePath != ""
 }
 
-// HasModRoot reports whether a main module is present.
+// HasModRoot reports whether a main module or main modules are present.
 // HasModRoot may return false even if Enabled returns true: for example, 'get'
 // does not require a main module.
 func HasModRoot() bool {
@@ -646,24 +646,34 @@ func die() {
        if cfg.Getenv("GO111MODULE") == "off" {
                base.Fatalf("go: modules disabled by GO111MODULE=off; see 'go help modules'")
        }
-       if inWorkspaceMode() {
-               base.Fatalf("go: no modules were found in the current workspace; see 'go help work'")
-       }
-       if dir, name := findAltConfig(base.Cwd()); dir != "" {
-               rel, err := filepath.Rel(base.Cwd(), dir)
-               if err != nil {
-                       rel = dir
-               }
-               cdCmd := ""
-               if rel != "." {
-                       cdCmd = fmt.Sprintf("cd %s && ", rel)
+       if !inWorkspaceMode() {
+               if dir, name := findAltConfig(base.Cwd()); dir != "" {
+                       rel, err := filepath.Rel(base.Cwd(), dir)
+                       if err != nil {
+                               rel = dir
+                       }
+                       cdCmd := ""
+                       if rel != "." {
+                               cdCmd = fmt.Sprintf("cd %s && ", rel)
+                       }
+                       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, but found %s in %s\n\tto create a module there, run:\n\t%sgo mod init", name, dir, cdCmd)
        }
        base.Fatal(ErrNoModRoot)
 }
 
-var ErrNoModRoot = errors.New("go.mod file not found in current directory or any parent directory; see 'go help modules'")
+// noMainModulesError returns the appropriate error if there is no main module or
+// main modules depending on whether the go command is in workspace mode.
+type noMainModulesError struct{}
+
+func (e noMainModulesError) Error() string {
+       if inWorkspaceMode() {
+               return "no modules were found in the current workspace; see 'go help work'"
+       }
+       return "go.mod file not found in current directory or any parent directory; see 'go help modules'"
+}
+
+var ErrNoModRoot noMainModulesError
 
 type goModDirtyError struct{}
 

diff --git a/src/cmd/go/testdata/script/work_no_mod_root_issue54419.txt b/src/cmd/go/testdata/script/work_no_mod_root_issue54419.txt
new file mode 100644 (file)
index 0000000..385044d
--- /dev/null
+++ b/src/cmd/go/testdata/script/work_no_mod_root_issue54419.txt
@@ -0,0 +1,13 @@
+cd m
+! go mod download
+stderr 'no modules were found in the current workspace'
+
+! go list -m all
+stderr 'no modules were found in the current workspace'
+
+-- go.work --
+go 1.25
+-- m/go.mod --
+module example.com/m
+
+go 1.25