1 files changed, 75 insertions, 0 deletions
diff --git a/src/cmd/gofix/oserrorstring.go b/src/cmd/gofix/oserrorstring.go
new file mode 100644
index 000000000..5e61ab952
--- /dev/null
+++ b/src/cmd/gofix/oserrorstring.go
@@ -0,0 +1,75 @@
+// 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"
+)
+
+var oserrorstringFix = fix{
+	"oserrorstring",
+	oserrorstring,
+	`Replace os.ErrorString() conversions with calls to os.NewError().
+
+http://codereview.appspot.com/4607052
+`,
+}
+
+func init() {
+	register(oserrorstringFix)
+}
+
+func oserrorstring(f *ast.File) bool {
+	if !imports(f, "os") {
+		return false
+	}
+
+	fixed := false
+	walk(f, func(n interface{}) {
+		// The conversion os.ErrorString(x) looks like a call
+		// of os.ErrorString with one argument.
+		if call := callExpr(n, "os", "ErrorString"); call != nil {
+			// os.ErrorString(args) -> os.NewError(args)
+			call.Fun.(*ast.SelectorExpr).Sel.Name = "NewError"
+			// os.ErrorString(args) -> os.NewError(args)
+			call.Fun.(*ast.SelectorExpr).Sel.Name = "NewError"
+			fixed = true
+			return
+		}
+
+		// Remove os.Error type from variable declarations initialized
+		// with an os.NewError.
+		// (An *ast.ValueSpec may also be used in a const declaration
+		// but those won't be initialized with a call to os.NewError.)
+		if spec, ok := n.(*ast.ValueSpec); ok &&
+			len(spec.Names) == 1 &&
+			isPkgDot(spec.Type, "os", "Error") &&
+			len(spec.Values) == 1 &&
+			callExpr(spec.Values[0], "os", "NewError") != nil {
+			// var name os.Error = os.NewError(x) ->
+			// var name          = os.NewError(x)
+			spec.Type = nil
+			fixed = true
+			return
+		}
+
+		// Other occurrences of os.ErrorString are not fixed
+		// but they are rare.
+
+	})
+	return fixed
+}
+
+
+// callExpr returns the call expression if x is a call to pkg.name with one argument;
+// otherwise it returns nil.
+func callExpr(x interface{}, pkg, name string) *ast.CallExpr {
+	if call, ok := x.(*ast.CallExpr); ok &&
+		len(call.Args) == 1 &&
+		isPkgDot(call.Fun, pkg, name) {
+		return call
+	}
+	return nil
+}