cmd/go: limit test input file change detection to local GOROOT/GOPATH tree

We've had a series of problems with tests unexpectedly (and innocently)
looking at system files that appear to (but don't) change in meaningful ways,
like /dev/null on OS X having a modification time set to the current time.

Cut all these off by only applying file change detection to the local package
root: the GOROOT or specific sub-GOPATH in which the package being tested
is found.

(This means that if you test reads /tmp/x and you change /tmp/x, the cached
result will still be used. Don't do that, or else use -count=1.)

Fixes #23390.

Change-Id: I30b6dd194835deb645a040aea5e6e4f68af09edb
Reviewed-on: https://go-review.googlesource.com/87015
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

5 files changed, 82 insertions, 28 deletions

diff --git a/src/cmd/go/go_test.go b/src/cmd/go/go_test.go
index 42eea06dc2..02c63de57f 100644
--- a/src/cmd/go/go_test.go
+++ b/src/cmd/go/go_test.go
@@ -5307,6 +5307,30 @@ func TestTestCacheInputs(t *testing.T) {
 	tg.run("test", "testcache", "-run=DirList")
 	tg.grepStdout(`\(cached\)`, "did not cache")
 
+	tg.tempFile("file.txt", "")
+	tg.must(ioutil.WriteFile(filepath.Join(tg.pwd(), "testdata/src/testcache/testcachetmp_test.go"), []byte(`package testcache
+
+		import (
+			"os"
+			"testing"
+		)
+
+		func TestExternalFile(t *testing.T) {
+			os.Open(`+fmt.Sprintf("%q", tg.path("file.txt"))+`)
+			_, err := os.Stat(`+fmt.Sprintf("%q", tg.path("file.txt"))+`)
+			if err != nil {
+				t.Fatal(err)
+			}
+		}
+	`), 0666))
+	defer os.Remove(filepath.Join(tg.pwd(), "testdata/src/testcache/testcachetmp_test.go"))
+	tg.run("test", "testcache", "-run=ExternalFile")
+	tg.run("test", "testcache", "-run=ExternalFile")
+	tg.grepStdout(`\(cached\)`, "did not cache")
+	tg.must(os.Remove(filepath.Join(tg.tempdir, "file.txt")))
+	tg.run("test", "testcache", "-run=ExternalFile")
+	tg.grepStdout(`\(cached\)`, "did not cache")
+
 	switch runtime.GOOS {
 	case "nacl", "plan9", "windows":
 		// no shell scripts
diff --git a/src/cmd/go/internal/load/path.go b/src/cmd/go/internal/load/path.go
index 9cc85dd757..45a9e7b242 100644
--- a/src/cmd/go/internal/load/path.go
+++ b/src/cmd/go/internal/load/path.go
@@ -56,25 +56,3 @@ func expandPath(p string) string {
 	}
 	return p
 }
-
-// hasFilePathPrefix reports whether the filesystem path s begins with the
-// elements in prefix.
-func hasFilePathPrefix(s, prefix string) bool {
-	sv := strings.ToUpper(filepath.VolumeName(s))
-	pv := strings.ToUpper(filepath.VolumeName(prefix))
-	s = s[len(sv):]
-	prefix = prefix[len(pv):]
-	switch {
-	default:
-		return false
-	case sv != pv:
-		return false
-	case len(s) == len(prefix):
-		return s == prefix
-	case len(s) > len(prefix):
-		if prefix != "" && prefix[len(prefix)-1] == filepath.Separator {
-			return strings.HasPrefix(s, prefix)
-		}
-		return s[len(prefix)] == filepath.Separator && s[:len(prefix)] == prefix
-	}
-}
diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index 2b3d7fd0e1..a0d052a26f 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -520,13 +520,13 @@ func VendoredImportPath(parent *Package, path string) (found string) {
 
 	dir := filepath.Clean(parent.Dir)
 	root := filepath.Join(parent.Root, "src")
-	if !hasFilePathPrefix(dir, root) || parent.ImportPath != "command-line-arguments" && filepath.Join(root, parent.ImportPath) != dir {
+	if !str.HasFilePathPrefix(dir, root) || parent.ImportPath != "command-line-arguments" && filepath.Join(root, parent.ImportPath) != dir {
 		// Look for symlinks before reporting error.
 		dir = expandPath(dir)
 		root = expandPath(root)
 	}
 
-	if !hasFilePathPrefix(dir, root) || len(dir) <= len(root) || dir[len(root)] != filepath.Separator || parent.ImportPath != "command-line-arguments" && !parent.Internal.Local && filepath.Join(root, parent.ImportPath) != dir {
+	if !str.HasFilePathPrefix(dir, root) || len(dir) <= len(root) || dir[len(root)] != filepath.Separator || parent.ImportPath != "command-line-arguments" && !parent.Internal.Local && filepath.Join(root, parent.ImportPath) != dir {
 		base.Fatalf("unexpected directory layout:\n"+
 			"	import path: %s\n"+
 			"	root: %s\n"+
@@ -670,14 +670,14 @@ func disallowInternal(srcDir string, p *Package, stk *ImportStack) *Package {
 		i-- // rewind over slash in ".../internal"
 	}
 	parent := p.Dir[:i+len(p.Dir)-len(p.ImportPath)]
-	if hasFilePathPrefix(filepath.Clean(srcDir), filepath.Clean(parent)) {
+	if str.HasFilePathPrefix(filepath.Clean(srcDir), filepath.Clean(parent)) {
 		return p
 	}
 
 	// Look for symlinks before reporting error.
 	srcDir = expandPath(srcDir)
 	parent = expandPath(parent)
-	if hasFilePathPrefix(filepath.Clean(srcDir), filepath.Clean(parent)) {
+	if str.HasFilePathPrefix(filepath.Clean(srcDir), filepath.Clean(parent)) {
 		return p
 	}
 
@@ -770,14 +770,14 @@ func disallowVendorVisibility(srcDir string, p *Package, stk *ImportStack) *Pack
 		return p
 	}
 	parent := p.Dir[:truncateTo]
-	if hasFilePathPrefix(filepath.Clean(srcDir), filepath.Clean(parent)) {
+	if str.HasFilePathPrefix(filepath.Clean(srcDir), filepath.Clean(parent)) {
 		return p
 	}
 
 	// Look for symlinks before reporting error.
 	srcDir = expandPath(srcDir)
 	parent = expandPath(parent)
-	if hasFilePathPrefix(filepath.Clean(srcDir), filepath.Clean(parent)) {
+	if str.HasFilePathPrefix(filepath.Clean(srcDir), filepath.Clean(parent)) {
 		return p
 	}
 
diff --git a/src/cmd/go/internal/str/path.go b/src/cmd/go/internal/str/path.go
new file mode 100644
index 0000000000..84ca9d581e
--- /dev/null
+++ b/src/cmd/go/internal/str/path.go
@@ -0,0 +1,32 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package str
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+// HasFilePathPrefix reports whether the filesystem path s begins with the
+// elements in prefix.
+func HasFilePathPrefix(s, prefix string) bool {
+	sv := strings.ToUpper(filepath.VolumeName(s))
+	pv := strings.ToUpper(filepath.VolumeName(prefix))
+	s = s[len(sv):]
+	prefix = prefix[len(pv):]
+	switch {
+	default:
+		return false
+	case sv != pv:
+		return false
+	case len(s) == len(prefix):
+		return s == prefix
+	case len(s) > len(prefix):
+		if prefix != "" && prefix[len(prefix)-1] == filepath.Separator {
+			return strings.HasPrefix(s, prefix)
+		}
+		return s[len(prefix)] == filepath.Separator && s[:len(prefix)] == prefix
+	}
+}
diff --git a/src/cmd/go/internal/test/test.go b/src/cmd/go/internal/test/test.go
index f7f6c64a86..0bc27c17ea 100644
--- a/src/cmd/go/internal/test/test.go
+++ b/src/cmd/go/internal/test/test.go
@@ -1637,11 +1637,19 @@ func computeTestInputsID(a *work.Action, testlog []byte) (cache.ActionID, error)
 			if !filepath.IsAbs(name) {
 				name = filepath.Join(pwd, name)
 			}
+			if !inDir(name, a.Package.Root) {
+				// Do not recheck files outside the GOPATH or GOROOT root.
+				break
+			}
 			fmt.Fprintf(h, "stat %s %x\n", name, hashStat(name))
 		case "open":
 			if !filepath.IsAbs(name) {
 				name = filepath.Join(pwd, name)
 			}
+			if !inDir(name, a.Package.Root) {
+				// Do not recheck files outside the GOPATH or GOROOT root.
+				break
+			}
 			fh, err := hashOpen(name)
 			if err != nil {
 				if cache.DebugTest {
@@ -1656,6 +1664,18 @@ func computeTestInputsID(a *work.Action, testlog []byte) (cache.ActionID, error)
 	return sum, nil
 }
 
+func inDir(path, dir string) bool {
+	if str.HasFilePathPrefix(path, dir) {
+		return true
+	}
+	xpath, err1 := filepath.EvalSymlinks(path)
+	xdir, err2 := filepath.EvalSymlinks(dir)
+	if err1 == nil && err2 == nil && str.HasFilePathPrefix(xpath, xdir) {
+		return true
+	}
+	return false
+}
+
 func hashGetenv(name string) cache.ActionID {
 	h := cache.NewHash("getenv")
 	v, ok := os.LookupEnv(name)