cmd/compile: propagate correct line numbers in treecopy

Added a lineno parameter to treecopy and listtreecopy
(ignored if = 0).  When nodes are copied the copy is
assigned the non-zero lineno (normally this would be
the destination).

Fixes #8183

Change-Id: Iffb767a745093fb89aa08bf8a7692c2f0122be98
Reviewed-on: https://go-review.googlesource.com/10334Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/compile/internal/gc/dcl.go

@@ -313,18 +313,19 @@ func variter(vl *NodeList, t *Node, el *NodeList) *NodeList {
  * new_name_list [[type] = expr_list]
  */
 func constiter(vl *NodeList, t *Node, cl *NodeList) *NodeList {
+	lno := int32(0) // default is to leave line number alone in listtreecopy
 	if cl == nil {
 		if t != nil {
 			Yyerror("const declaration cannot have type without expression")
 		}
 		cl = lastconst
 		t = lasttype
+		lno = vl.N.Lineno
 	} else {
 		lastconst = cl
 		lasttype = t
 	}
-
-	cl = listtreecopy(cl)
+	cl = listtreecopy(cl, lno)
 
 	var v *Node
 	var c *Node

src/cmd/compile/internal/gc/order.go

@@ -498,7 +498,7 @@ func orderstmt(n *Node, order *Order) {
 
 		orderexpr(&n.Left, order, nil)
 		n.Left = ordersafeexpr(n.Left, order)
-		tmp1 := treecopy(n.Left)
+		tmp1 := treecopy(n.Left, 0)
 		if tmp1.Op == OINDEXMAP {
 			tmp1.Etype = 0 // now an rvalue not an lvalue
 		}

src/cmd/compile/internal/gc/racewalk.go

@@ -483,7 +483,7 @@ func callinstr(np **Node, init **NodeList, wr int, skip int) bool {
 			*np = n
 		}
 
-		n = treecopy(n)
+		n = treecopy(n, 0)
 		makeaddable(n)
 		var f *Node
 		if t.Etype == TSTRUCT || Isfixedarray(t) {

src/cmd/compile/internal/gc/subr.go

@@ -736,7 +736,12 @@ func aindex(b *Node, t *Type) *Type {
 	return r
 }
 
-func treecopy(n *Node) *Node {
+// treecopy recursively copies n, with the exception of
+// ONAME, OLITERAL, OTYPE, and non-iota ONONAME leaves.
+// Copies of iota ONONAME nodes are assigned the current
+// value of iota_. If lineno != 0, it sets the line number
+// of newly allocated nodes to lineno.
+func treecopy(n *Node, lineno int32) *Node {
 	if n == nil {
 		return nil
 	}
@@ -747,9 +752,12 @@ func treecopy(n *Node) *Node {
 		m = Nod(OXXX, nil, nil)
 		*m = *n
 		m.Orig = m
-		m.Left = treecopy(n.Left)
-		m.Right = treecopy(n.Right)
-		m.List = listtreecopy(n.List)
+		m.Left = treecopy(n.Left, lineno)
+		m.Right = treecopy(n.Right, lineno)
+		m.List = listtreecopy(n.List, lineno)
+		if lineno != -1 {
+			m.Lineno = lineno
+		}
 		if m.Defn != nil {
 			panic("abort")
 		}
@@ -764,6 +772,9 @@ func treecopy(n *Node) *Node {
 
 			*m = *n
 			m.Iota = iota_
+			if lineno != 0 {
+				m.Lineno = lineno
+			}
 			break
 		}
 		fallthrough
@@ -3092,10 +3103,10 @@ func Simsimtype(t *Type) int {
 	return et
 }
 
-func listtreecopy(l *NodeList) *NodeList {
+func listtreecopy(l *NodeList, lineno int32) *NodeList {
 	var out *NodeList
 	for ; l != nil; l = l.Next {
-		out = list(out, treecopy(l.N))
+		out = list(out, treecopy(l.N, lineno))
 	}
 	return out
 }

test/fixedbugs/issue8183.go

+// errorcheck
+
+// Copyright 2015 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.
+
+// Tests correct reporting of line numbers for errors involving iota,
+// Issue #8183.
+package foo
+
+const (
+	ok = byte(iota + 253)
+	bad
+	barn
+	bard // ERROR "constant 256 overflows byte"
+)
+
+const (
+	c = len([1 - iota]int{})
+	d
+	e // ERROR "array bound must be non-negative" "const initializer len\(composite literal\) is not a constant"
+	f // ERROR "array bound must be non-negative" "const initializer len\(composite literal\) is not a constant"
+)