broaden type inference from context (assignment statements)

compiler/checker/checker.odin

@@ -1727,7 +1727,7 @@ infer_statements :: proc(
 		case .Assignment:
 			value_type := infer_expr(checker, statement.expr, locals^[:], pkg, file, demanded, local_types)
 			if statement.target != ast.INVALID_EXPR {
-				_ = infer_expr(checker, statement.target, locals^[:], pkg, file, demanded, local_types)
+				target_type := infer_expr(checker, statement.target, locals^[:], pkg, file, demanded, local_types)
 				target_expr := checker.ast_module.exprs[statement.target]
 				if target_expr.kind == .Name && !symbol.is_valid(target_expr.qualifier) {
 					if local_index, ok := find_infer_local_index(locals^[:], target_expr.name); ok &&
@@ -1735,10 +1735,16 @@ infer_statements :: proc(
 						_ = merge_infer_local_type(checker, &locals^[local_index], value_type, local_types)
 					}
 				}
+				// Push the target's concrete type backward onto the RHS so a const used
+				// only in an assignment (e.g. `x += speed`) resolves, mirroring how
+				// declarations and returns demand their context (record_demand self-gates
+				// on a concrete demand and only touches fitting open slots).
+				_ = record_demand(checker, statement.expr, target_type, locals^[:], local_types, pkg, file)
 			} else if statement.name != checker.sink_symbol {
 				if local_index, ok := find_infer_local_index(locals^[:], statement.name); ok &&
 				   locals^[local_index].mutable {
 					_ = merge_infer_local_type(checker, &locals^[local_index], value_type, local_types)
+					_ = record_demand(checker, statement.expr, locals^[local_index].type, locals^[:], local_types, pkg, file)
 				}
 			}
 		case .Expression: