From 8b7383a008c8875637d37c0df18e8773cc0bd06c Mon Sep 17 00:00:00 2001
From: NeilBrown <neil@brown.name>
Date: Tue, 30 Apr 2019 14:00:03 +1000
Subject: [PATCH] oceani: delay constant assignment test to type analysis.

When we get more complex types, it will be easier to
guard against assigning to a constant during type analysis.

Signed-off-by: NeilBrown <neil@brown.name>
---
 csrc/oceani.mdc | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/csrc/oceani.mdc b/csrc/oceani.mdc
index edc3b12..0760674 100644
--- a/csrc/oceani.mdc
+++ b/csrc/oceani.mdc
@@ -1415,7 +1415,7 @@ propagation is needed.
 
 ###### ast
 
-	enum val_rules {Rnolabel = 1<<0, Rboolok = 1<<1};
+	enum val_rules {Rnolabel = 1<<0, Rboolok = 1<<1, Rnoconstant = 2<<1};
 
 ###### format cases
 	case 'r':
@@ -1765,6 +1765,14 @@ link to find the primary instance.
 		}
 		if (v->merged)
 			v = v->merged;
+		if (v->constant && (rules & Rnoconstant)) {
+			type_err(c, "error: Cannot assign to a constant: %v",
+			         prog, NULL, 0, NULL);
+			type_err(c, "info: name was defined as a constant here",
+			         v->where_decl, NULL, 0, NULL);
+			*ok = 0;
+			return v->val.type;
+		}
 		if (v->val.type == NULL) {
 			if (type && *ok != 0) {
 				v->val = val_prepare(type);
@@ -2488,20 +2496,12 @@ it is declared, and error will be raised as the name is created as
 	Declare,
 
 ###### SimpleStatement Grammar
-	| Variable = Expression ${ {
-			struct var *v = cast(var, $1);
-
+	| Variable = Expression ${
 			$0 = new(binode);
 			$0->op = Assign;
 			$0->left = $<1;
 			$0->right = $<3;
-			if (v->var && v->var->constant) {
-				type_err(config2context(config), "Cannot assign to a constant: %v",
-				         $0->left, NULL, 0, NULL);
-				type_err(config2context(config), "name was defined as a constant here",
-				         v->var->where_decl, NULL, 0, NULL);
-			}
-		} }$
+		}$
 	| VariableDecl = Expression ${
 			$0 = new(binode);
 			$0->op = Declare;
@@ -2567,8 +2567,11 @@ it is declared, and error will be raised as the name is created as
 	case Declare:
 		/* Both must match and not be labels,
 		 * Type must support 'dup',
-		 * result is Tnone */
-		t = propagate_types(b->left, c, ok, NULL, Rnolabel);
+		 * For Assign, left must not be constant.
+		 * result is Tnone
+		 */
+		t = propagate_types(b->left, c, ok, NULL,
+		                    Rnolabel | (b->op == Assign ? Rnoconstant : 0));
 		if (!b->right)
 			return Tnone;
 
@@ -2580,7 +2583,8 @@ it is declared, and error will be raised as the name is created as
 		} else {
 			t = propagate_types(b->right, c, ok, NULL, Rnolabel);
 			if (t)
-				propagate_types(b->left, c, ok, t, 0);
+				propagate_types(b->left, c, ok, t,
+				                (b->op == Assign ? Rnoconstant : 0));
 		}
 		if (t && t->dup == NULL) {
 			type_err(c, "error: cannot assign value of type %1", b, t, 0, NULL);
-- 
2.43.0