1 files changed, 44 insertions, 0 deletions
diff --git a/src/cmd/vet/assign.go b/src/cmd/vet/assign.go
new file mode 100644
index 000000000..a11f0f875
--- /dev/null
+++ b/src/cmd/vet/assign.go
@@ -0,0 +1,44 @@
+// Copyright 2013 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.
+
+/*
+This file contains the code to check for useless assignments.
+*/
+
+package main
+
+import (
+	"go/ast"
+	"go/token"
+	"reflect"
+)
+
+// TODO: should also check for assignments to struct fields inside methods
+// that are on T instead of *T.
+
+// checkAssignStmt checks for assignments of the form "<expr> = <expr>".
+// These are almost always useless, and even when they aren't they are usually a mistake.
+func (f *File) checkAssignStmt(stmt *ast.AssignStmt) {
+	if !vet("assign") {
+		return
+	}
+	if stmt.Tok != token.ASSIGN {
+		return // ignore :=
+	}
+	if len(stmt.Lhs) != len(stmt.Rhs) {
+		// If LHS and RHS have different cardinality, they can't be the same.
+		return
+	}
+	for i, lhs := range stmt.Lhs {
+		rhs := stmt.Rhs[i]
+		if reflect.TypeOf(lhs) != reflect.TypeOf(rhs) {
+			continue // short-circuit the heavy-weight gofmt check
+		}
+		le := f.gofmt(lhs)
+		re := f.gofmt(rhs)
+		if le == re {
+			f.Warnf(stmt.Pos(), "self-assignment of %s to %s", re, le)
+		}
+	}
+}