imports: extend findImports to return a boolean, rename, that tells

goimports to use the package name as a local qualifier in an import.
For example, if findImports("pkg", "X") returns ("foo/bar",
rename=true), then goimports adds the import line:
  import pkg "foo/bar"
to satisfy uses of pkg.X in the file.

This change doesn't add any implementations of rename=true, though one
is sketched in a TODO.

LGTM=crawshaw
R=crawshaw, rsc
CC=bradfitz, golang-codereviews
https://golang.org/cl/76400050

imports/fix.go

@@ -93,6 +93,7 @@ func fixImports(fset *token.FileSet, f *ast.File) (added []string, err error) {
 	searches := 0
 	type result struct {
 		ipath string
+		name  string
 		err   error
 	}
 	results := make(chan result)
@@ -101,8 +102,12 @@ func fixImports(fset *token.FileSet, f *ast.File) (added []string, err error) {
 			continue // skip over packages already imported
 		}
 		go func(pkgName string, symbols map[string]bool) {
-			ipath, err := findImport(pkgName, symbols)
+			ipath, rename, err := findImport(pkgName, symbols)
-			results <- result{ipath, err}
+			r := result{ipath: ipath, err: err}
+			if rename {
+				r.name = pkgName
+			}
+			results <- r
 		}(pkgName, symbols)
 		searches++
 	}
@@ -112,7 +117,11 @@ func fixImports(fset *token.FileSet, f *ast.File) (added []string, err error) {
 			return nil, result.err
 		}
 		if result.ipath != "" {
-			astutil.AddImport(fset, f, result.ipath)
+			if result.name != "" {
+				astutil.AddNamedImport(fset, f, result.name, result.ipath)
+			} else {
+				astutil.AddImport(fset, f, result.ipath)
+			}
 			added = append(added, result.ipath)
 		}
 	}
@@ -270,14 +279,19 @@ func loadExportsGoPath(dir string) map[string]bool {
 // extended by adding a file with an init function.
 var findImport = findImportGoPath
 
-func findImportGoPath(pkgName string, symbols map[string]bool) (string, error) {
+func findImportGoPath(pkgName string, symbols map[string]bool) (string, bool, error) {
 	// Fast path for the standard library.
 	// In the common case we hopefully never have to scan the GOPATH, which can
 	// be slow with moving disks.
-	if pkg, ok := findImportStdlib(pkgName, symbols); ok {
+	if pkg, rename, ok := findImportStdlib(pkgName, symbols); ok {
-		return pkg, nil
+		return pkg, rename, nil
 	}
 
+	// TODO(sameer): look at the import lines for other Go files in the
+	// local directory, since the user is likely to import the same packages
+	// in the current Go file.  Return rename=true when the other Go files
+	// use a renamed package that's also used in the current file.
+
 	pkgIndexOnce.Do(loadPkgIndex)
 
 	// Collect exports for packages with matching names.
@@ -311,7 +325,7 @@ func findImportGoPath(pkgName string, symbols map[string]bool) (string, error) {
 		}
 	}
 	if len(pkgs) == 0 {
-		return "", nil
+		return "", false, nil
 	}
 
 	// If there are multiple candidate packages, the shortest one wins.
@@ -323,7 +337,7 @@ func findImportGoPath(pkgName string, symbols map[string]bool) (string, error) {
 			shortest = importPath
 		}
 	}
-	return shortest, nil
+	return shortest, false, nil
 }
 
 type visitFn func(node ast.Node) ast.Visitor
@@ -332,17 +346,17 @@ func (fn visitFn) Visit(node ast.Node) ast.Visitor {
 	return fn(node)
 }
 
-func findImportStdlib(shortPkg string, symbols map[string]bool) (importPath string, ok bool) {
+func findImportStdlib(shortPkg string, symbols map[string]bool) (importPath string, rename, ok bool) {
 	for symbol := range symbols {
 		path := stdlib[shortPkg+"."+symbol]
 		if path == "" {
-			return "", false
+			return "", false, false
 		}
 		if importPath != "" && importPath != path {
 			// Ambiguous. Symbols pointed to different things.
-			return "", false
+			return "", false, false
 		}
 		importPath = path
 	}
-	return importPath, importPath != ""
+	return importPath, false, importPath != ""
 }

imports/fix_test.go

@@ -505,6 +505,20 @@ var (
 	b = gu.a
 	c = fmt.Printf
 )
+`,
+	},
+
+	{
+		name: "renamed package",
+		in: `package main
+
+var _ = str.HasPrefix
+`,
+		out: `package main
+
+import str "strings"
+
+var _ = str.HasPrefix
 `,
 	},
 }
@@ -519,9 +533,10 @@ func TestFixImports(t *testing.T) {
 		"zip":       "archive/zip",
 		"bytes":     "bytes",
 		"snappy":    "code.google.com/p/snappy-go/snappy",
+		"str":       "strings",
 	}
-	findImport = func(pkgName string, symbols map[string]bool) (string, error) {
+	findImport = func(pkgName string, symbols map[string]bool) (string, bool, error) {
-		return simplePkgs[pkgName], nil
+		return simplePkgs[pkgName], pkgName == "str", nil
 	}
 
 	for _, tt := range tests {
@@ -577,20 +592,20 @@ type Buffer2 struct {}
 		build.Default.GOPATH = oldGOPATH
 	}()
 
-	got, err := findImportGoPath("bytes", map[string]bool{"Buffer2": true})
+	got, rename, err := findImportGoPath("bytes", map[string]bool{"Buffer2": true})
 	if err != nil {
 		t.Fatal(err)
 	}
-	if got != bytesPkgPath {
+	if got != bytesPkgPath || rename {
-		t.Errorf(`findImportGoPath("bytes", Buffer2 ...)=%q, want "%s"`, got, bytesPkgPath)
+		t.Errorf(`findImportGoPath("bytes", Buffer2 ...)=%q, %t, want "%s", false`, got, rename, bytesPkgPath)
 	}
 
-	got, err = findImportGoPath("bytes", map[string]bool{"Missing": true})
+	got, rename, err = findImportGoPath("bytes", map[string]bool{"Missing": true})
 	if err != nil {
 		t.Fatal(err)
 	}
-	if got != "" {
+	if got != "" || rename {
-		t.Errorf(`findImportGoPath("bytes", Missing ...)=%q, want ""`, got)
+		t.Errorf(`findImportGoPath("bytes", Missing ...)=%q, %t, want "", false`, got, rename)
 	}
 }
 
@@ -607,12 +622,12 @@ func TestFindImportStdlib(t *testing.T) {
 		{"ioutil", []string{"Discard"}, "io/ioutil"},
 	}
 	for _, tt := range tests {
-		got, ok := findImportStdlib(tt.pkg, strSet(tt.symbols))
+		got, rename, ok := findImportStdlib(tt.pkg, strSet(tt.symbols))
 		if (got != "") != ok {
 			t.Error("findImportStdlib return value inconsistent")
 		}
-		if got != tt.want {
+		if got != tt.want || rename {
-			t.Errorf("findImportStdlib(%q, %q) = %q; want %q", tt.pkg, tt.symbols, got, tt.want)
+			t.Errorf("findImportStdlib(%q, %q) = %q, %t; want %q, false", tt.pkg, tt.symbols, got, rename, tt.want)
 		}
 	}
 }