cmd/go/internal/modload: do not prune the module root when walking directories

When walking filesystem paths to locate packages, we normally prune
out subdirectories with names beginning with ".", "_", or equal to
"testdata". However, we should not prune out such a directory if it is
at or above the module root, since its name is not part of the package
path.

Fixes #28481
Updates #27852

Change-Id: Ice82b1f908afaab50f5592f6c38ca6a0fe911edf
Reviewed-on: https://go-review.googlesource.com/c/go/+/196297
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/cmd/go/internal/modload/search.go b/src/cmd/go/internal/modload/search.go
index d82386eca30538511800a4cd408a0004cdd4665e..98c384161b541538eff67e13e2c16912895489f2 100644 (file)
--- a/src/cmd/go/internal/modload/search.go
+++ b/src/cmd/go/internal/modload/search.go
@@ -48,16 +48,20 @@ func matchPackages(pattern string, tags map[string]bool, useStd bool, modules []
                                return nil
                        }
 
-                       // Don't use GOROOT/src but do walk down into it.
-                       if path == root && importPathRoot == "" {
-                               return nil
-                       }
-
                        want := true
-                       // Avoid .foo, _foo, and testdata directory trees.
-                       _, elem := filepath.Split(path)
-                       if strings.HasPrefix(elem, ".") || strings.HasPrefix(elem, "_") || elem == "testdata" {
-                               want = false
+                       elem := ""
+
+                       // Don't use GOROOT/src but do walk down into it.
+                       if path == root {
+                               if importPathRoot == "" {
+                                       return nil
+                               }
+                       } else {
+                               // Avoid .foo, _foo, and testdata subdirectory trees.
+                               _, elem = filepath.Split(path)
+                               if strings.HasPrefix(elem, ".") || strings.HasPrefix(elem, "_") || elem == "testdata" {
+                                       want = false
+                               }
                        }
 
                        name := importPathRoot + filepath.ToSlash(path[len(root):])

diff --git a/src/cmd/go/testdata/script/mod_in_testdata_dir.txt b/src/cmd/go/testdata/script/mod_in_testdata_dir.txt
new file mode 100644 (file)
index 0000000..f582569
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_in_testdata_dir.txt
@@ -0,0 +1,45 @@
+# Regression test for golang.org/issue/28481:
+# 'mod tidy' removed dependencies if the module root was
+# within a directory named 'testdata' or '_foo'.
+
+env GO111MODULE=on
+
+# A module should be allowed in a directory named testdata.
+cd $WORK/testdata
+go mod init testdata.tld/foo
+
+# Building a package within that module should resolve its dependencies.
+go build
+grep 'rsc.io/quote' go.mod
+
+# Tidying the module should preserve those dependencies.
+go mod tidy
+grep 'rsc.io/quote' go.mod
+
+[short] stop
+
+# Vendoring the module's dependencies should work too.
+go mod vendor
+exists vendor/rsc.io/quote
+
+# The same should work in directories with names starting with underscores.
+cd $WORK/_ignored
+go mod init testdata.tld/foo
+
+go build
+grep 'rsc.io/quote' go.mod
+
+go mod tidy
+grep 'rsc.io/quote' go.mod
+
+go mod vendor
+exists vendor/rsc.io/quote
+
+-- $WORK/testdata/main.go --
+package foo
+
+import _ "rsc.io/quote"
+-- $WORK/_ignored/main.go --
+package foo
+
+import _ "rsc.io/quote"