cmd/compile: simplify noding const declarations

By grouping all the logic into constDecl, we're able to get rid of the
lastconst and lasttype globals, and simplify the logic slightly. Still
clunky, but much easier to reason about.

Change-Id: I446696c31084b3bfc1fd5d3651655a81ddd159ab
Reviewed-on: https://go-review.googlesource.com/36023
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 52 insertions, 24 deletions

diff --git a/src/cmd/compile/internal/gc/noder.go b/src/cmd/compile/internal/gc/noder.go
index 2de5b18f7c..14dc1a1d87 100644
--- a/src/cmd/compile/internal/gc/noder.go
+++ b/src/cmd/compile/internal/gc/noder.go
@@ -117,9 +117,7 @@ func (p *noder) node() {
 }
 
 func (p *noder) decls(decls []syntax.Decl) (l []*Node) {
-	var lastConstGroup *syntax.Group
-	var lastConstRHS []*Node
-	var iotaVal int64
+	var cs constState
 
 	for _, decl := range decls {
 		p.lineno(decl)
@@ -131,23 +129,7 @@ func (p *noder) decls(decls []syntax.Decl) (l []*Node) {
 			l = append(l, p.varDecl(decl)...)
 
 		case *syntax.ConstDecl:
-			// Tricky to handle golang.org/issue/15550 correctly.
-
-			if decl.Group == nil || decl.Group != lastConstGroup {
-				iotaVal = 0
-				lastConstRHS = nil
-			}
-
-			lastconst = lastConstRHS
-
-			l = append(l, p.constDecl(decl, iotaVal)...)
-
-			lastConstRHS = lastconst
-			lastconst = nil
-
-			iotaVal++
-
-			lastConstGroup = decl.Group
+			l = append(l, p.constDecl(decl, &cs)...)
 
 		case *syntax.TypeDecl:
 			l = append(l, p.typeDecl(decl))
@@ -222,16 +204,62 @@ func (p *noder) varDecl(decl *syntax.VarDecl) []*Node {
 	return variter(names, typ, exprs)
 }
 
-func (p *noder) constDecl(decl *syntax.ConstDecl, iotaVal int64) []*Node {
+type constState struct {
+	group  *syntax.Group
+	typ    *Node
+	values []*Node
+	iota   int64
+}
+
+func (p *noder) constDecl(decl *syntax.ConstDecl, cs *constState) []*Node {
+	if decl.Group == nil || decl.Group != cs.group {
+		*cs = constState{
+			group: decl.Group,
+		}
+	}
+
 	names := p.declNames(decl.NameList)
 	typ := p.typeExprOrNil(decl.Type)
 
-	var exprs []*Node
+	var values []*Node
 	if decl.Values != nil {
-		exprs = p.exprList(decl.Values)
+		values = p.exprList(decl.Values)
+		cs.typ, cs.values = typ, values
+	} else {
+		if typ != nil {
+			yyerror("const declaration cannot have type without expression")
+		}
+		typ, values = cs.typ, cs.values
 	}
 
-	return constiter(names, typ, exprs, iotaVal)
+	var nn []*Node
+	for i, n := range names {
+		if i >= len(values) {
+			yyerror("missing value in const declaration")
+			break
+		}
+		v := values[i]
+		if decl.Values == nil {
+			v = treecopy(v, n.Pos)
+		}
+
+		n.Op = OLITERAL
+		declare(n, dclcontext)
+
+		n.Name.Param.Ntype = typ
+		n.Name.Defn = v
+		n.SetIota(cs.iota)
+
+		nn = append(nn, p.nod(decl, ODCLCONST, n, nil))
+	}
+
+	if len(values) > len(names) {
+		yyerror("extra expression in const declaration")
+	}
+
+	cs.iota++
+
+	return nn
 }
 
 func (p *noder) typeDecl(decl *syntax.TypeDecl) *Node {