mutable decl syntax change

compiler/parser/parser.odin

@@ -1868,15 +1868,35 @@ parse_statement :: proc(parser: ^Parser) -> ast.Stmt_Id {
 			had_type = true
 		}
 		operator := current(parser)
-		if operator.kind == .Colon_Colon || operator.kind == .Equal {
+		if had_type && operator.kind == .Equal {
+			diagnostic := source.add(
+				parser.diagnostics,
+				operator.span,
+				"mutable declarations use ':=' instead of '='",
+			)
+			for current(parser).kind != .Newline &&
+			    current(parser).kind != .Right_Brace &&
+			    current(parser).kind != .Eof {
+				advance(parser)
+			}
+			id := ast.stmt_id(len(parser.module.statements))
+			append(&parser.module.statements, ast.Stmt{
+				kind=.Invalid,
+				span=span_from(name.span, operator.span),
+				expr=ast.INVALID_EXPR,
+				diagnostic=diagnostic,
+			})
+			return id
+		}
+		is_sink := name.kind == .Underscore && operator.kind == .Equal
+		if operator.kind == .Colon_Colon || operator.kind == .Colon_Equal || is_sink {
 			advance(parser)
 			skip_newlines(parser)
-			kind := ast.Stmt_Kind.Assignment
-			immutable := false
-			if operator.kind == .Colon_Colon || had_type {
-				kind = .Declaration
-				immutable = operator.kind == .Colon_Colon
+			kind := ast.Stmt_Kind.Declaration
+			if is_sink {
+				kind = .Assignment
 			}
+			immutable := operator.kind == .Colon_Colon
 			// A labeled value block (`x :: blk: { … yield :blk v }`): the label lets a
 			// `yield :blk` exit the block past a nested `if`. Block-init body + label.
 			if current(parser).kind == .Identifier && peek(parser).kind == .Colon {
@@ -1954,6 +1974,11 @@ parse_statement :: proc(parser: ^Parser) -> ast.Stmt_Id {
 	}
 
 	expr := parse_expression(parser)
+	assignment_name := symbol.INVALID
+	target_expr := parser.module.exprs[expr]
+	if target_expr.kind == .Name && !symbol.is_valid(target_expr.qualifier) {
+		assignment_name = target_expr.name
+	}
 	if _, ok := allow(parser, .Equal); ok {
 		skip_newlines(parser)
 		// A labeled value block assigned to a complex target (`a[i] = blk: { … }`).
@@ -1964,6 +1989,7 @@ parse_statement :: proc(parser: ^Parser) -> ast.Stmt_Id {
 			append(&parser.module.statements, ast.Stmt{
 				kind=.Assignment,
 				span=span_from(parser.module.exprs[expr].span, previous(parser).span),
+				name=assignment_name,
 				target=expr,
 				label=label,
 				expr=ast.INVALID_EXPR,
@@ -1980,6 +2006,7 @@ parse_statement :: proc(parser: ^Parser) -> ast.Stmt_Id {
 			append(&parser.module.statements, ast.Stmt{
 				kind=.Assignment,
 				span=span_from(parser.module.exprs[expr].span, brace.span),
+				name=assignment_name,
 				target=expr,
 				expr=ast.INVALID_EXPR,
 				body=body,
@@ -1995,6 +2022,7 @@ parse_statement :: proc(parser: ^Parser) -> ast.Stmt_Id {
 			append(&parser.module.statements, ast.Stmt{
 				kind=.Assignment,
 				span=span_from(parser.module.exprs[expr].span, previous(parser).span),
+				name=assignment_name,
 				target=expr,
 				value_control_flow=true,
 				expr=ast.INVALID_EXPR,
@@ -2008,6 +2036,7 @@ parse_statement :: proc(parser: ^Parser) -> ast.Stmt_Id {
 		append(&parser.module.statements, ast.Stmt{
 			kind=.Assignment,
 			span=span_from(parser.module.exprs[expr].span, parser.module.exprs[value].span),
+			name=assignment_name,
 			target=expr,
 			expr=value,
 			diagnostic=source.INVALID_DIAGNOSTIC,
@@ -3312,8 +3341,16 @@ parse_top_level :: proc(parser: ^Parser) {
 		type_syntax = parse_type(parser)
 	}
 	operator := current(parser)
-	if operator.kind != .Colon_Colon && operator.kind != .Equal {
-		source.add(parser.diagnostics, operator.span, "expected '::' or '=' after top-level name")
+	if operator.kind == .Equal {
+		source.add(parser.diagnostics, operator.span, "mutable declarations use ':=' instead of '='")
+		for current(parser).kind != .Newline && current(parser).kind != .Eof {
+			advance(parser)
+		}
+		_ = finish_statement(parser)
+		return
+	}
+	if operator.kind != .Colon_Colon && operator.kind != .Colon_Equal {
+		source.add(parser.diagnostics, operator.span, "expected '::' or ':=' after top-level name")
 		_ = finish_statement(parser)
 		return
 	}