imports: assume import x/y/v2 is package y

This will be true in general for Go modules, so it's the right fallback.
Note that if the package can be found in GOPATH, the code still
uses the actual package name from GOPATH, so this only changes
the fallback path. The fallback path is what currently executes
when using modules (because they are not in GOPATH).

Change-Id: I3d48517583eae9431e139371d363ce354c89340a
Reviewed-on: https://go-review.googlesource.com/122616
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

imports/fix.go

@@ -19,6 +19,7 @@ import (
 	"path"
 	"path/filepath"
 	"sort"
+	"strconv"
 	"strings"
 	"sync"
 
@@ -367,9 +368,19 @@ func fixImports(fset *token.FileSet, f *ast.File, filename string) (added []stri
 // importPathToName returns the package name for the given import path.
 var importPathToName func(importPath, srcDir string) (packageName string) = importPathToNameGoPath
 
-// importPathToNameBasic assumes the package name is the base of import path.
+// importPathToNameBasic assumes the package name is the base of import path,
+// except that if the path ends in foo/vN, it assumes the package name is foo.
 func importPathToNameBasic(importPath, srcDir string) (packageName string) {
-	return path.Base(importPath)
+	base := path.Base(importPath)
+	if strings.HasPrefix(base, "v") {
+		if _, err := strconv.Atoi(base[1:]); err == nil {
+			dir := path.Dir(importPath)
+			if dir != "." {
+				return path.Base(dir)
+			}
+		}
+	}
+	return base
 }
 
 // importPathToNameGoPath finds out the actual package name, as declared in its .go files.

imports/fix_test.go

@@ -1140,6 +1140,32 @@ var (
 
 }
 
+// Test for x/y/v2 convention for package y.
+func TestFixModuleVersion(t *testing.T) {
+	testConfig{}.test(t, func(t *goimportTest) {
+		input := `package p
+
+import (
+	"fmt"
+
+	"foo/v2"
+)
+
+var (
+	_ = fmt.Print
+	_ = foo.Foo
+)
+`
+		buf, err := Process(filepath.Join(t.gopath, "src/mypkg.com/outpkg/toformat.go"), []byte(input), &Options{})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got := string(buf); got != input {
+			t.Fatalf("results differ\nGOT:\n%s\nWANT:\n%s\n", got, input)
+		}
+	})
+}
+
 // Test for correctly identifying the name of a vendored package when it
 // differs from its directory name. In this test, the import line
 // "mypkg.com/mypkg.v1" would be removed if goimports wasn't able to detect
@@ -1670,8 +1696,8 @@ func TestImportPathToNameGoPathParse(t *testing.T) {
 func TestIgnoreConfiguration(t *testing.T) {
 	testConfig{
 		gopathFiles: map[string]string{
-			".goimportsignore":                                     "# comment line\n\n example.net", // tests comment, blank line, whitespace trimming
-			"example.net/pkg/pkg.go":                               "package pkg\nconst X = 1",
+			".goimportsignore":       "# comment line\n\n example.net", // tests comment, blank line, whitespace trimming
+			"example.net/pkg/pkg.go": "package pkg\nconst X = 1",
 			"otherwise-longer-so-worse.example.net/foo/pkg/pkg.go": "package pkg\nconst X = 1",
 		},
 	}.test(t, func(t *goimportTest) {