Commit 0a188190b3b2b42906d0cc38f101b010bc07b414 | zig

author	Veikka Tuominen <git@vexu.eu> 2022-11-08 19:48:21+02:00
committer	Veikka Tuominen <git@vexu.eu> 2022-11-11 17:59:53+02:00
log	0a188190b3b2b42906d0cc38f101b010bc07b414
tree	60f1914391ff3467f5eb97d389a18dbe73e1684f
parent	d2cc55109a64aaf004384b942e08e95829b9341f

AstGen: make pointless discard error more strict

The error should only happen as a result of `_ = <expr>` not
for an operand of a break expression that is discarded.

Closes #13212

2 files changed, 20 insertions(+), 5 deletions(-)

src
- AstGen.zig
test
- cases
  - compile_errors
    pointless discard.zig

src/AstGen.zig+12-5

 @@ -339,6 +339,8 @@ pub const ResultInfo = struct {
         fn_arg,
         /// The expression is the right-hand side of an initializer for a `const` variable
         const_init,
+        /// The expression is the right-hand side of an assignment expression.
+        assignment,
         /// No specific operator in particular.
         none,
     };
 @@ -3216,7 +3218,7 @@ fn assign(gz: *GenZir, scope: *Scope, infix_node: Ast.Node.Index) InnerError!voi
         // This intentionally does not support `@"_"` syntax.
         const ident_name = tree.tokenSlice(main_tokens[lhs]);
         if (mem.eql(u8, ident_name, "_")) {
-            _ = try expr(gz, scope, .{ .rl = .discard }, rhs);
+            _ = try expr(gz, scope, .{ .rl = .discard, .ctx = .assignment }, rhs);
             return;
         }
     }
 @@ -7088,7 +7090,7 @@ fn localVarRef(
             if (local_val.name == name_str_index) {
                 // Locals cannot shadow anything, so we do not need to look for ambiguous
                 // references in this case.
-                if (ri.rl == .discard) {
+                if (ri.rl == .discard and ri.ctx == .assignment) {
                     local_val.discarded = ident_token;
                 } else {
                     local_val.used = ident_token;
 @@ -7111,7 +7113,7 @@ fn localVarRef(
         .local_ptr => {
             const local_ptr = s.cast(Scope.LocalPtr).?;
             if (local_ptr.name == name_str_index) {
-                if (ri.rl == .discard) {
+                if (ri.rl == .discard and ri.ctx == .assignment) {
                     local_ptr.discarded = ident_token;
                 } else {
                     local_ptr.used = ident_token;
 @@ -10672,14 +10674,19 @@ const GenZir = struct {
                 gz.break_result_info = parent_ri;
             },
-            .discard, .none, .ref => {
+            .none, .ref => {
                 gz.rl_ty_inst = .none;
                 gz.break_result_info = parent_ri;
             },
+            .discard => {
+                gz.rl_ty_inst = .none;
+                gz.break_result_info = .{ .rl = .discard };
+            },
             .ptr => |ptr_res| {
                 gz.rl_ty_inst = .none;
-                gz.break_result_info = .{ .rl = .{ .ptr = .{ .inst = ptr_res.inst } } };
+                gz.break_result_info = .{ .rl = .{ .ptr = .{ .inst = ptr_res.inst } }, .ctx = parent_ri.ctx };
             },
             .inferred_ptr => |ptr| {

test/cases/compile_errors/pointless discard.zig +8

...	@@ -3,6 +3,14 @@ export fn foo() void {	...	@@ -3,6 +3,14 @@ export fn foo() void {
3	x += 1;	3	x += 1;
4	_ = x;	4	_ = x;
5	}	5	}
		6	export fn bar() void {
		7	var b: u32 = 1;
		8	_ = blk: {
		9	const a = 1;
		10	b = a;
		11	break :blk a;
		12	};
		13	}
6		14
7	// error	15	// error
8	// backend=stage2	16	// backend=stage2