cmd/go: mention go.work when local path outside modules in go.work

In workspace mode, if a user lists a package or patternthat's inside a
module that's not listed in go.work, mention that the package or pattern
is outside the modules listed in go.work so the user has a better idea
of how to fix the issue.

(Question: it's valid in those flows to add a pattern that points into
the module cache. Should we expand the error to say "package outside
modules listed in go.work file or contained in module cache"? That seems
clunky (and is the uncommon case) which is why I didn't do so in this
case, but it's possible)

Fixes #49632

Change-Id: I3f0ea1b2f566d52a8079b58593fcc5cc095e7a41
Reviewed-on: https://go-review.googlesource.com/c/go/+/384236
Trust: Michael Matloob <matloob@golang.org>
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 10 insertions, 2 deletions

diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index 617b634d263..a4a7cb263eb 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -479,7 +479,11 @@ func matchLocalDirs(ctx context.Context, modRoots []string, m *search.Match, rs
 		}
 		if !found && search.InDir(absDir, cfg.GOROOTsrc) == "" && pathInModuleCache(ctx, absDir, rs) == "" {
 			m.Dirs = []string{}
-			m.AddError(fmt.Errorf("directory prefix %s outside available modules", base.ShortPath(absDir)))
+			scope := "main module or its selected dependencies"
+			if inWorkspaceMode() {
+				scope = "modules listed in go.work or their selected dependencies"
+			}
+			m.AddError(fmt.Errorf("directory prefix %s does not contain %s", base.ShortPath(absDir), scope))
 			return
 		}
 	}
@@ -601,7 +605,11 @@ func resolveLocalPackage(ctx context.Context, dir string, rs *Requirements) (str
 
 	pkg := pathInModuleCache(ctx, absDir, rs)
 	if pkg == "" {
-		return "", fmt.Errorf("directory %s outside available modules", base.ShortPath(absDir))
+		scope := "main module or its selected dependencies"
+		if inWorkspaceMode() {
+			scope = "modules listed in go.work or their selected dependencies"
+		}
+		return "", fmt.Errorf("directory %s outside %s", base.ShortPath(absDir), scope)
 	}
 	return pkg, nil
 }