go/ast/astutil: add function DeleteNamedImport.

DeleteNamedImport deletes the import with a given
name and path from a parsed file, if present.

imports uses this function to delete named imports.

Fixes golang/go#8149.

Change-Id: I84539d5627191c45f06db2d008507aee4d3b1eb2
Reviewed-on: https://go-review.googlesource.com/19951
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

go/ast/astutil/imports.go

@@ -148,6 +148,11 @@ func AddNamedImport(fset *token.FileSet, f *ast.File, name, ipath string) (added
 
 // DeleteImport deletes the import path from the file f, if present.
 func DeleteImport(fset *token.FileSet, f *ast.File, path string) (deleted bool) {
+	return DeleteNamedImport(fset, f, "", path)
+}
+
+// DeleteNamedImport deletes the import with the given name and path from the file f, if present.
+func DeleteNamedImport(fset *token.FileSet, f *ast.File, name, path string) (deleted bool) {
 	var delspecs []*ast.ImportSpec
 
 	// Find the import nodes that import path, if any.
@@ -160,6 +165,12 @@ func DeleteImport(fset *token.FileSet, f *ast.File, path string) (deleted bool)
 		for j := 0; j < len(gen.Specs); j++ {
 			spec := gen.Specs[j]
 			impspec := spec.(*ast.ImportSpec)
+			if impspec.Name == nil && name != "" {
+				continue
+			}
+			if impspec.Name != nil && impspec.Name.Name != name {
+				continue
+			}
 			if importPath(impspec) != path {
 				continue
 			}

go/ast/astutil/imports_test.go

@@ -761,6 +761,36 @@ import (
 )
 `,
 		out: `package main
+`,
+	},
+	{
+		name:       "import.18",
+		renamedPkg: "x",
+		pkg:        "fmt",
+		in: `package main
+
+import (
+	"fmt"
+	x "fmt"
+)
+`,
+		out: `package main
+
+import "fmt"
+`,
+	},
+	{
+		name:       "import.18",
+		renamedPkg: "x",
+		pkg:        "fmt",
+		in: `package main
+
+import x "fmt"
+import y "fmt"
+`,
+		out: `package main
+
+import y "fmt"
 `,
 	},
 }
@@ -768,7 +798,7 @@ import (
 func TestDeleteImport(t *testing.T) {
 	for _, test := range deleteTests {
 		file := parse(t, test.name, test.in)
-		DeleteImport(fset, file, test.pkg)
+		DeleteNamedImport(fset, file, test.renamedPkg, test.pkg)
 		if got := print(t, test.name, file); got != test.out {
 			t.Errorf("%s:\ngot: %s\nwant: %s", test.name, got, test.out)
 		}

imports/fix.go

@@ -90,18 +90,22 @@ func fixImports(fset *token.FileSet, f *ast.File, filename string) (added []stri
 	ast.Walk(visitor, f)
 
 	// Nil out any unused ImportSpecs, to be removed in following passes
-	unusedImport := map[string]bool{}
+	unusedImport := map[string]string{}
 	for pkg, is := range decls {
 		if refs[pkg] == nil && pkg != "_" && pkg != "." {
-			unusedImport[strings.Trim(is.Path.Value, `"`)] = true
+			name := ""
+			if is.Name != nil {
+				name = is.Name.Name
+			}
+			unusedImport[strings.Trim(is.Path.Value, `"`)] = name
 		}
 	}
-	for ipath := range unusedImport {
+	for ipath, name := range unusedImport {
 		if ipath == "C" {
 			// Don't remove cgo stuff.
 			continue
 		}
-		astutil.DeleteImport(fset, f, ipath)
+		astutil.DeleteNamedImport(fset, f, name, ipath)
 	}
 
 	// Search for imports matching potential package references.

imports/fix_test.go

@@ -726,6 +726,27 @@ func main() { fmt.Println() }
 
 import "fmt"
 
+func main() { fmt.Println() }
+`,
+	},
+
+	// Unused named import is mistaken for unnamed import
+	// golang.org/issue/8149
+	{
+		name: "issue 8149",
+		in: `package main
+
+import (
+	"fmt"
+	x "fmt"
+)
+
+func main() { fmt.Println() }
+`,
+		out: `package main
+
+import "fmt"
+
 func main() { fmt.Println() }
 `,
 	},