gofix: test import insertion, deletion

Small change to go/ast, go/parser, go/printer so that
gofix can delete the blank line left from deleting an import.

R=golang-dev, bradfitz, adg
CC=golang-dev
https://golang.org/cl/5321046

src/cmd/gofix/fix.go

@@ -19,7 +19,7 @@ type fix struct {
 	desc string
 }
 
-// main runs sort.Sort(fixes) after init process is done.
+// main runs sort.Sort(fixes) before printing list of fixes.
 type fixlist []fix
 
 func (f fixlist) Len() int           { return len(f) }
@@ -316,6 +316,20 @@ func importPath(s *ast.ImportSpec) string {
 	return ""
 }
 
+// declImports reports whether gen contains an import of path.
+func declImports(gen *ast.GenDecl, path string) bool {
+	if gen.Tok != token.IMPORT {
+		return false
+	}
+	for _, spec := range gen.Specs {
+		impspec := spec.(*ast.ImportSpec)
+		if importPath(impspec) == path {
+			return true
+		}
+	}
+	return false
+}
+
 // isPkgDot returns true if t is the expression "pkg.name"
 // where pkg is an imported identifier.
 func isPkgDot(t ast.Expr, pkg, name string) bool {
@@ -486,12 +500,18 @@ func addImport(f *ast.File, path string) {
 	var impdecl *ast.GenDecl
 
 	// Find an import decl to add to.
-	for _, decl := range f.Decls {
+	var lastImport int = -1
+	for i, decl := range f.Decls {
 		gen, ok := decl.(*ast.GenDecl)
 
 		if ok && gen.Tok == token.IMPORT {
-			impdecl = gen
-			break
+			lastImport = i
+			// Do not add to import "C", to avoid disrupting the
+			// association with its doc comment, breaking cgo.
+			if !declImports(gen, "C") {
+				impdecl = gen
+				break
+			}
 		}
 	}
 
@@ -501,8 +521,8 @@ func addImport(f *ast.File, path string) {
 			Tok: token.IMPORT,
 		}
 		f.Decls = append(f.Decls, nil)
-		copy(f.Decls[1:], f.Decls)
-		f.Decls[0] = impdecl
+		copy(f.Decls[lastImport+2:], f.Decls[lastImport+1:])
+		f.Decls[lastImport+1] = impdecl
 	}
 
 	// Ensure the import decl has parentheses, if needed.
@@ -540,7 +560,6 @@ func deleteImport(f *ast.File, path string) {
 		}
 		for j, spec := range gen.Specs {
 			impspec := spec.(*ast.ImportSpec)
-
 			if oldImport != impspec {
 				continue
 			}
@@ -558,7 +577,13 @@ func deleteImport(f *ast.File, path string) {
 			} else if len(gen.Specs) == 1 {
 				gen.Lparen = token.NoPos // drop parens
 			}
-
+			if j > 0 {
+				// We deleted an entry but now there will be
+				// a blank line-sized hole where the import was.
+				// Close the hole by making the previous
+				// import appear to "end" where this one did.
+				gen.Specs[j-1].(*ast.ImportSpec).EndPos = impspec.End()
+			}
 			break
 		}
 	}

src/cmd/gofix/import_test.go

@@ -0,0 +1,269 @@
+// Copyright 2011 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 "go/ast"
+
+func init() {
+	addTestCases(importTests, nil)
+}
+
+var importTests = []testCase{
+	{
+		Name: "import.0",
+		Fn:   addImportFn("os"),
+		In: `package main
+
+import (
+	"os"
+)
+`,
+		Out: `package main
+
+import (
+	"os"
+)
+`,
+	},
+	{
+		Name: "import.1",
+		Fn:   addImportFn("os"),
+		In: `package main
+`,
+		Out: `package main
+
+import "os"
+`,
+	},
+	{
+		Name: "import.2",
+		Fn:   addImportFn("os"),
+		In: `package main
+
+// Comment
+import "C"
+`,
+		Out: `package main
+
+// Comment
+import "C"
+import "os"
+`,
+	},
+	{
+		Name: "import.3",
+		Fn:   addImportFn("os"),
+		In: `package main
+
+// Comment
+import "C"
+
+import (
+	"io"
+	"utf8"
+)
+`,
+		Out: `package main
+
+// Comment
+import "C"
+
+import (
+	"io"
+	"os"
+	"utf8"
+)
+`,
+	},
+	{
+		Name: "import.4",
+		Fn:   deleteImportFn("os"),
+		In: `package main
+
+import (
+	"os"
+)
+`,
+		Out: `package main
+`,
+	},
+	{
+		Name: "import.5",
+		Fn:   deleteImportFn("os"),
+		In: `package main
+
+// Comment
+import "C"
+import "os"
+`,
+		Out: `package main
+
+// Comment
+import "C"
+`,
+	},
+	{
+		Name: "import.6",
+		Fn:   deleteImportFn("os"),
+		In: `package main
+
+// Comment
+import "C"
+
+import (
+	"io"
+	"os"
+	"utf8"
+)
+`,
+		Out: `package main
+
+// Comment
+import "C"
+
+import (
+	"io"
+	"utf8"
+)
+`,
+	},
+	{
+		Name: "import.7",
+		Fn:   deleteImportFn("io"),
+		In: `package main
+
+import (
+	"io"   // a
+	"os"   // b
+	"utf8" // c
+)
+`,
+		Out: `package main
+
+import (
+	// a
+	"os"   // b
+	"utf8" // c
+)
+`,
+	},
+	{
+		Name: "import.8",
+		Fn:   deleteImportFn("os"),
+		In: `package main
+
+import (
+	"io"   // a
+	"os"   // b
+	"utf8" // c
+)
+`,
+		Out: `package main
+
+import (
+	"io" // a
+	// b
+	"utf8" // c
+)
+`,
+	},
+	{
+		Name: "import.9",
+		Fn:   deleteImportFn("utf8"),
+		In: `package main
+
+import (
+	"io"   // a
+	"os"   // b
+	"utf8" // c
+)
+`,
+		Out: `package main
+
+import (
+	"io" // a
+	"os" // b
+	// c
+)
+`,
+	},
+	{
+		Name: "import.10",
+		Fn:   deleteImportFn("io"),
+		In: `package main
+
+import (
+	"io"
+	"os"
+	"utf8"
+)
+`,
+		Out: `package main
+
+import (
+	"os"
+	"utf8"
+)
+`,
+	},
+	{
+		Name: "import.11",
+		Fn:   deleteImportFn("os"),
+		In: `package main
+
+import (
+	"io"
+	"os"
+	"utf8"
+)
+`,
+		Out: `package main
+
+import (
+	"io"
+	"utf8"
+)
+`,
+	},
+	{
+		Name: "import.12",
+		Fn:   deleteImportFn("utf8"),
+		In: `package main
+
+import (
+	"io"
+	"os"
+	"utf8"
+)
+`,
+		Out: `package main
+
+import (
+	"io"
+	"os"
+)
+`,
+	},
+}
+
+func addImportFn(path string) func(*ast.File) bool {
+	return func(f *ast.File) bool {
+		if !imports(f, path) {
+			addImport(f, path)
+			return true
+		}
+		return false
+	}
+}
+
+func deleteImportFn(path string) func(*ast.File) bool {
+	return func(f *ast.File) bool {
+		if imports(f, path) {
+			deleteImport(f, path)
+			return true
+		}
+		return false
+	}
+}

src/pkg/go/ast/ast.go

@@ -752,6 +752,7 @@ type (
 		Name    *Ident        // local package name (including "."); or nil
 		Path    *BasicLit     // import path
 		Comment *CommentGroup // line comments; or nil
+		EndPos  token.Pos     // end of spec (overrides Path.Pos if nonzero)
 	}
 
 	// A ValueSpec node represents a constant or variable declaration
@@ -785,7 +786,13 @@ func (s *ImportSpec) Pos() token.Pos {
 func (s *ValueSpec) Pos() token.Pos { return s.Names[0].Pos() }
 func (s *TypeSpec) Pos() token.Pos  { return s.Name.Pos() }
 
-func (s *ImportSpec) End() token.Pos { return s.Path.End() }
+func (s *ImportSpec) End() token.Pos {
+	if s.EndPos != 0 {
+		return s.EndPos
+	}
+	return s.Path.End()
+}
+
 func (s *ValueSpec) End() token.Pos {
 	if n := len(s.Values); n > 0 {
 		return s.Values[n-1].End()

src/pkg/go/parser/parser.go

@@ -1909,7 +1909,7 @@ func parseImportSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
 	p.expectSemi() // call before accessing p.linecomment
 
 	// collect imports
-	spec := &ast.ImportSpec{doc, ident, path, p.lineComment}
+	spec := &ast.ImportSpec{doc, ident, path, p.lineComment, token.NoPos}
 	p.imports = append(p.imports, spec)
 
 	return spec

src/pkg/go/printer/nodes.go

@@ -1278,6 +1278,7 @@ func (p *printer) spec(spec ast.Spec, n int, doIndent bool, multiLine *bool) {
 		}
 		p.expr(s.Path, multiLine)
 		p.setComment(s.Comment)
+		p.print(s.EndPos)
 
 	case *ast.ValueSpec:
 		if n != 1 {