go/ast: respect ImportSpec.EndPos

Fixes #2566.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5541068

src/cmd/gofix/import_test.go

@@ -351,7 +351,7 @@ var addr = flag.String("addr", ":1718", "http service address") // Q=17, R=18
 `,
 	},
 	{
-		Name: "import.3",
+		Name: "import.17",
 		Fn:   addImportFn("x/y/z", "x/a/c"),
 		In: `package main
 
@@ -382,6 +382,26 @@ import (
 
 	"d/f"
 )
+`,
+	},
+	{
+		Name: "import.18",
+		Fn:   addDelImportFn("e", "o"),
+		In: `package main
+
+import (
+	"f"
+	"o"
+	"z"
+)
+`,
+		Out: `package main
+
+import (
+	"e"
+	"f"
+	"z"
+)
 `,
 	},
 }
@@ -409,6 +429,21 @@ func deleteImportFn(path string) func(*ast.File) bool {
 	}
 }
 
+func addDelImportFn(p1 string, p2 string) func(*ast.File) bool {
+	return func(f *ast.File) bool {
+		fixed := false
+		if !imports(f, p1) {
+			addImport(f, p1)
+			fixed = true
+		}
+		if imports(f, p2) {
+			deleteImport(f, p2)
+			fixed = true
+		}
+		return fixed
+	}
+}
+
 func rewriteImportFn(oldnew ...string) func(*ast.File) bool {
 	return func(f *ast.File) bool {
 		fixed := false

src/pkg/go/ast/import.go

@@ -67,12 +67,7 @@ func sortSpecs(fset *token.FileSet, f *File, specs []Spec) {
 	// Record positions for specs.
 	pos := make([]posSpan, len(specs))
 	for i, s := range specs {
-		// Cannot use s.End(), because it looks at len(s.Path.Value),
-		// and that string might have gotten longer or shorter.
-		// Instead, use s.Pos()+1, which is guaranteed to be > s.Pos()
-		// and still before the original end of the string, since any
-		// string literal must be at least 2 characters ("" or ``).
-		pos[i] = posSpan{s.Pos(), s.Pos() + 1}
+		pos[i] = posSpan{s.Pos(), s.End()}
 	}
 
 	// Identify comments in this range.