cmd/go: show warnings about symlinks only for patterns containing ...

Go commands show a warning message any time a pattern is expanded and a
symlink to a directory is encountered. For monorepo with non Go projects
using symlinks underneath, the output of go commands could be spammed by
this warning.

This commit includes the behavior change to only print this warning when
there's a pattern containing ... .

Fixes #35941

Change-Id: I094da2628bcd47b86fee8c6529d1066aa013a43b
Reviewed-on: https://go-review.googlesource.com/c/go/+/311890
Run-TryBot: Caleb Spare <cespare@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
Trust: Michael Matloob <matloob@golang.org>

src/cmd/go/internal/modload/search.go

@@ -86,7 +86,7 @@ func matchPackages(ctx context.Context, m *search.Match, tags map[string]bool, f
 			}
 
 			if !fi.IsDir() {
-				if fi.Mode()&fs.ModeSymlink != 0 && want {
+				if fi.Mode()&fs.ModeSymlink != 0 && want && strings.Contains(m.Pattern(), "...") {
 					if target, err := fsys.Stat(path); err == nil && target.IsDir() {
 						fmt.Fprintf(os.Stderr, "warning: ignoring symlink %s\n", path)
 					}

src/cmd/go/internal/search/search.go

@@ -155,7 +155,7 @@ func (m *Match) MatchPackages() {
 			}
 
 			if !fi.IsDir() {
-				if fi.Mode()&fs.ModeSymlink != 0 && want {
+				if fi.Mode()&fs.ModeSymlink != 0 && want && strings.Contains(m.pattern, "...") {
 					if target, err := fsys.Stat(path); err == nil && target.IsDir() {
 						fmt.Fprintf(os.Stderr, "warning: ignoring symlink %s\n", path)
 					}

src/cmd/go/testdata/script/list_symlink_issue35941.txt

@@ -0,0 +1,18 @@
+[!symlink] skip
+env GO111MODULE=off
+
+# Issue 35941: suppress symlink warnings when running 'go list all'.
+symlink goproj/css -> $GOPATH/src/css
+
+go list all
+! stderr 'warning: ignoring symlink'
+
+# Show symlink warnings when patterns contain '...'.
+go list goproj/...
+stderr 'warning: ignoring symlink'
+
+-- goproj/a.go --
+package a
+
+-- css/index.css --
+body {}

src/cmd/go/testdata/script/mod_tidy_symlink_issue35941.txt

@@ -0,0 +1,36 @@
+env GO111MODULE=on
+[!symlink] skip
+
+cd m
+symlink symlink -> ../outside
+
+cp go.mod go.mod.orig
+
+# Issue 35941: suppress symlink warnings when running 'go mod tidy'.
+# 'go mod tidy' should not scan packages in symlinked subdirectories.
+go mod tidy
+! stderr 'warning: ignoring symlink'
+cmp go.mod go.mod.orig
+
+! go build ./symlink
+stderr '^symlink[\\/]symlink.go:3:8: module example.net/unresolved provides package example.net/unresolved and is replaced but not required; to add it:\n\tgo get example.net/unresolved@v0.1.0$'
+
+-- m/go.mod --
+module example.net/m
+
+go 1.16
+
+replace example.net/unresolved v0.1.0 => ../unresolved
+-- m/a.go --
+package a
+-- outside/symlink.go --
+package symlink
+
+import _ "example.net/unresolved"
+-- unresolved/go.mod --
+module example.net/unresolved
+
+go 1.16
+-- unresolved/unresolved.go --
+// Package unresolved exists, but 'go mod tidy' won't add it.
+package unresolved