1 files changed, 67 insertions, 0 deletions
diff --git a/src/cmd/gofmt/simplify.go b/src/cmd/gofmt/simplify.go
new file mode 100644
index 000000000..bcc67c4a6
--- /dev/null
+++ b/src/cmd/gofmt/simplify.go
@@ -0,0 +1,67 @@
+// Copyright 2010 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"
+	"reflect"
+)
+
+
+type simplifier struct{}
+
+func (s *simplifier) Visit(node ast.Node) ast.Visitor {
+	switch n := node.(type) {
+	case *ast.CompositeLit:
+		// array, slice, and map composite literals may be simplified
+		outer := n
+		var eltType ast.Expr
+		switch typ := outer.Type.(type) {
+		case *ast.ArrayType:
+			eltType = typ.Elt
+		case *ast.MapType:
+			eltType = typ.Value
+		}
+
+		if eltType != nil {
+			typ := reflect.NewValue(eltType)
+			for _, x := range outer.Elts {
+				// look at value of indexed/named elements
+				if t, ok := x.(*ast.KeyValueExpr); ok {
+					x = t.Value
+				}
+				simplify(x)
+				// if the element is a composite literal and its literal type
+				// matches the outer literal's element type exactly, the inner
+				// literal type may be omitted
+				if inner, ok := x.(*ast.CompositeLit); ok {
+					if match(nil, typ, reflect.NewValue(inner.Type)) {
+						inner.Type = nil
+					}
+				}
+			}
+
+			// node was simplified - stop walk (there are no subnodes to simplify)
+			return nil
+		}
+
+	case *ast.RangeStmt:
+		// range of the form: for x, _ = range v {...}
+		// can be simplified to: for x = range v {...}
+		if n.Value != nil {
+			if ident, ok := n.Value.(*ast.Ident); ok && ident.Name == "_" {
+				n.Value = nil
+			}
+		}
+	}
+
+	return s
+}
+
+
+func simplify(node ast.Node) {
+	var s simplifier
+	ast.Walk(&s, node)
+}