cmd/guru: handle source file aliasing gracefully

Resolve symlinks in GOPATH or source file path in order to find correct package.

Fixes golang/go#17515

Change-Id: Iaf7e85578fce040b329427ce6f51948a69e57a39
Reviewed-on: https://go-review.googlesource.com/33858
Reviewed-by: Alan Donovan <adonovan@google.com>

cmd/guru/unit_test.go

@@ -0,0 +1,85 @@
+// Copyright 2013 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 main
+
+import (
+	"fmt"
+	"go/build"
+	"io/ioutil"
+	"os"
+	"strings"
+	"testing"
+)
+
+// Unit tests for internal guru functions
+
+func TestIssue17515(t *testing.T) {
+	// Tests handling of symlinks in function guessImportPath
+	// If we have Go code inside $HOME/go/src and create a symlink $HOME/src to it
+	// there are 4 possible cases that need to be tested:
+	// (1) absolute & absolute: GOPATH=$HOME/go/src file=$HOME/go/src/test/test.go
+	// (2) absolute & symlink:  GOPATH=$HOME/go/src file=$HOME/src/test/test.go
+	// (3) symlink & symlink:   GOPATH=$HOME/src file=$HOME/src/test/test.go
+	// (4) symlink & absolute:  GOPATH=$HOME/src file= $HOME/go/src/test/test.go
+
+	// Create a temporary home directory under /tmp
+	home, err := ioutil.TempDir(os.TempDir(), "home")
+	if err != nil {
+		t.Errorf("Unable to create a temporary directory in %s", os.TempDir())
+	}
+
+	// create filepath /tmp/home/go/src/test/test.go
+	if err = os.MkdirAll(home+"/go/src/test", 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	// symlink between /tmp/home/go/src and /tmp/home/src
+	if err = os.Symlink(home+"/go/src", home+"/src"); err != nil {
+		t.Fatal(err)
+	}
+
+	// Defer tear down (removing files, symlinks)
+	defer os.RemoveAll(home)
+
+	var buildContext = build.Default
+
+	// Success test cases
+	for _, test := range []struct {
+		gopath, filename, wantSrcdir string
+	}{
+		{home + "/go", home + "/go/src/test/test.go", home + "/go/src"},
+		{home + "/go", home + "/src/test/test.go", home + "/go/src"},
+		{home, home + "/src/test/test.go", home + "/src"},
+		{home, home + "/go/src/test/test.go", home + "/src"},
+	} {
+		buildContext.GOPATH = test.gopath
+		srcdir, importPath, err := guessImportPath(test.filename, &buildContext)
+		if srcdir != test.wantSrcdir || importPath != "test" || err != nil {
+			t.Errorf("guessImportPath(%v, %v) = %v, %v, %v; want %v, %v, %v",
+				test.filename, test.gopath, srcdir, importPath, err, test.wantSrcdir, "test", "nil")
+		}
+	}
+	// Function to format expected error message
+	errFormat := func(fpath string) string {
+		return fmt.Sprintf("can't evaluate symlinks of %s", fpath)
+	}
+
+	// Failure test cases
+	for _, test := range []struct {
+		gopath, filename, wantErr string
+	}{
+		{home + "/go", home + "/go/src/fake/test.go", errFormat(home + "/go/src/fake")},
+		{home + "/go", home + "/src/fake/test.go", errFormat(home + "/src/fake")},
+		{home, home + "/src/fake/test.go", errFormat(home + "/src/fake")},
+		{home, home + "/go/src/fake/test.go", errFormat(home + "/go/src/fake")},
+	} {
+		buildContext.GOPATH = test.gopath
+		srcdir, importPath, err := guessImportPath(test.filename, &buildContext)
+		if !strings.HasPrefix(fmt.Sprint(err), test.wantErr) {
+			t.Errorf("guessImportPath(%v, %v) = %v, %v, %v; want %v, %v, %v",
+				test.filename, test.gopath, srcdir, importPath, err, "", "", test.wantErr)
+		}
+	}
+}

cmd/guru/what.go

@@ -169,11 +169,16 @@ func what(q *Query) error {
 func guessImportPath(filename string, buildContext *build.Context) (srcdir, importPath string, err error) {
 	absFile, err := filepath.Abs(filename)
 	if err != nil {
-		err = fmt.Errorf("can't form absolute path of %s", filename)
-		return
+		return "", "", fmt.Errorf("can't form absolute path of %s: %v", filename, err)
 	}
-	absFileDir := segments(filepath.Dir(absFile))
 
+	absFileDir := filepath.Dir(absFile)
+	resolvedAbsFileDir, err := filepath.EvalSymlinks(absFileDir)
+	if err != nil {
+		return "", "", fmt.Errorf("can't evaluate symlinks of %s: %v", absFileDir, err)
+	}
+
+	segmentedAbsFileDir := segments(resolvedAbsFileDir)
 	// Find the innermost directory in $GOPATH that encloses filename.
 	minD := 1024
 	for _, gopathDir := range buildContext.SrcDirs() {
@@ -181,14 +186,19 @@ func guessImportPath(filename string, buildContext *build.Context) (srcdir, impo
 		if err != nil {
 			continue // e.g. non-existent dir on $GOPATH
 		}
-		d := prefixLen(segments(absDir), absFileDir)
+		resolvedAbsDir, err := filepath.EvalSymlinks(absDir)
+		if err != nil {
+			continue // e.g. non-existent dir on $GOPATH
+		}
+
+		d := prefixLen(segments(resolvedAbsDir), segmentedAbsFileDir)
 		// If there are multiple matches,
 		// prefer the innermost enclosing directory
 		// (smallest d).
 		if d >= 0 && d < minD {
 			minD = d
 			srcdir = gopathDir
-			importPath = strings.Join(absFileDir[len(absFileDir)-minD:], string(os.PathSeparator))
+			importPath = strings.Join(segmentedAbsFileDir[len(segmentedAbsFileDir)-minD:], string(os.PathSeparator))
 		}
 	}
 	if srcdir == "" {