reject invalid map key types at compile time

R=ken
OCL=25720
CL=25720

src/cmd/gc/go.h

@@ -657,6 +657,7 @@ int	isslice(Type*);
 int	isinter(Type*);
 int	isnilinter(Type*);
 int	isddd(Type*);
+Type*	maptype(Type*, Type*);
 Type*	dclmethod(Type*);
 Type*	methtype(Type*);
 int	methconv(Type*);

src/cmd/gc/go.y

@@ -1019,9 +1019,7 @@ convtype:
 |	LMAP '[' type ']' type
 	{
 		// map literal
-		$$ = typ(TMAP);
-		$$->down = $3;
-		$$->type = $5;
+		$$ = maptype($3, $5);
 	}
 |	structtype
 |	'(' type ')'
@@ -1126,9 +1124,7 @@ Aothertype:
 	}
 |	LMAP '[' type ']' Atype
 	{
-		$$ = typ(TMAP);
-		$$->down = $3;
-		$$->type = $5;
+		$$ = maptype($3, $5);
 	}
 |	'*' Atype
 	{
@@ -1160,9 +1156,7 @@ Bothertype:
 	}
 |	LMAP '[' type ']' Btype
 	{
-		$$ = typ(TMAP);
-		$$->down = $3;
-		$$->type = $5;
+		$$ = maptype($3, $5);
 	}
 |	'*' Btype
 	{
@@ -1806,9 +1800,7 @@ hidden_type1:
 	}
 |	LMAP '[' hidden_type ']' hidden_type
 	{
-		$$ = typ(TMAP);
-		$$->down = $3;
-		$$->type = $5;
+		$$ = maptype($3, $5);
 	}
 |	LSTRUCT '{' ohidden_structdcl_list '}'
 	{

src/cmd/gc/subr.c

@@ -305,6 +305,25 @@ algtype(Type *t)
 	return a;
 }
 
+Type*
+maptype(Type *key, Type *val)
+{
+	Type *t;
+
+	if(key != nil && key->etype != TANY && algtype(key) == ANOEQ)
+		yyerror("invalid map key type %T", key);
+	t = typ(TMAP);
+	t->down = key;
+	t->type = val;
+	return t;
+}
+
+int
+iskeytype(Type *t)
+{
+	return algtype(t) != ANOEQ;
+}
+
 Node*
 list(Node *a, Node *b)
 {