parser: make missing semicolon error point to the end of the previous token

lib/std/zig/Ast.zig

@@ -64,6 +64,17 @@ pub fn renderToArrayList(tree: Ast, buffer: *std.ArrayList(u8)) RenderError!void
     return @import("./render.zig").renderTree(buffer, tree);
 }
 
+/// Returns an extra offset for column and byte offset of errors that
+/// should point after the token in the error message.
+pub fn errorOffset(tree:Ast, error_tag: Error.Tag, token: TokenIndex) u32 {
+    return switch (error_tag) {
+        .expected_semi_after_decl,
+        .expected_semi_after_stmt,
+        => @intCast(u32, tree.tokenSlice(token).len),
+        else => 0,
+    };
+}
+
 pub fn tokenLocation(self: Ast, start_offset: ByteOffset, token_index: TokenIndex) Location {
     var loc = Location{
         .line = 0,
@@ -306,6 +317,13 @@ pub fn renderError(tree: Ast, parse_error: Error, stream: anytype) !void {
             return stream.writeAll("function prototype has parameter after varargs");
         },
 
+        .expected_semi_after_decl => {
+            return stream.writeAll("expected ';' after declaration");
+        },
+        .expected_semi_after_stmt => {
+            return stream.writeAll("expected ';' after statement");
+        },
+
         .expected_token => {
             const found_tag = token_tags[parse_error.token];
             const expected_symbol = parse_error.extra.expected_tag.symbol();
@@ -2495,6 +2513,10 @@ pub const Error = struct {
         unattached_doc_comment,
         varargs_nonfinal,
 
+        // these have `token` set to token after which a semicolon was expected
+        expected_semi_after_decl,
+        expected_semi_after_stmt,
+
         /// `expected_tag` is populated.
         expected_token,
     };

lib/std/zig/parse.zig

@@ -586,7 +586,7 @@ const Parser = struct {
         const thread_local_token = p.eatToken(.keyword_threadlocal);
         const var_decl = try p.parseVarDecl();
         if (var_decl != 0) {
-            _ = try p.expectToken(.semicolon);
+            try p.expectSemicolon(.expected_semi_after_decl, false);
             return var_decl;
         }
         if (thread_local_token != null) {
@@ -614,7 +614,7 @@ const Parser = struct {
     fn expectUsingNamespace(p: *Parser) !Node.Index {
         const usingnamespace_token = p.assertToken(.keyword_usingnamespace);
         const expr = try p.expectExpr();
-        _ = try p.expectToken(.semicolon);
+        try p.expectSemicolon(.expected_semi_after_decl, false);
         return p.addNode(.{
             .tag = .@"usingnamespace",
             .main_token = usingnamespace_token,
@@ -851,7 +851,7 @@ const Parser = struct {
 
         const var_decl = try p.parseVarDecl();
         if (var_decl != 0) {
-            _ = try p.expectTokenRecoverable(.semicolon);
+            try p.expectSemicolon(.expected_semi_after_decl, true);
             return var_decl;
         }
 
@@ -915,7 +915,7 @@ const Parser = struct {
 
         const assign_expr = try p.parseAssignExpr();
         if (assign_expr != 0) {
-            _ = try p.expectTokenRecoverable(.semicolon);
+            try p.expectSemicolon(.expected_semi_after_stmt, true);
             return assign_expr;
         }
 
@@ -1205,7 +1205,7 @@ const Parser = struct {
         }
         const assign_expr = try p.parseAssignExpr();
         if (assign_expr != 0) {
-            _ = try p.expectTokenRecoverable(.semicolon);
+            try p.expectSemicolon(.expected_semi_after_stmt, true);
             return assign_expr;
         }
         return null_node;
@@ -3664,6 +3664,15 @@ const Parser = struct {
         }
     }
 
+    fn expectSemicolon(p: *Parser, tag: AstError.Tag, recoverable: bool) Error!void {
+        if (p.token_tags[p.tok_i] == .semicolon) {
+            _ = p.nextToken();
+            return;
+        }
+        try p.warnMsg(.{ .tag = tag, .token = p.tok_i - 1 });
+        if (!recoverable) return error.ParseError;
+    }
+
     fn nextToken(p: *Parser) TokenIndex {
         const result = p.tok_i;
         p.tok_i += 1;

src/Module.zig

@@ -2995,13 +2995,14 @@ pub fn astGenFile(mod: *Module, file: *File) !void {
         const token_starts = file.tree.tokens.items(.start);
         const token_tags = file.tree.tokens.items(.tag);
 
+        const extra_offset = file.tree.errorOffset(parse_err.tag, parse_err.token);
         try file.tree.renderError(parse_err, msg.writer());
         const err_msg = try gpa.create(ErrorMsg);
         err_msg.* = .{
             .src_loc = .{
                 .file_scope = file,
                 .parent_decl_node = 0,
-                .lazy = .{ .byte_abs = token_starts[parse_err.token] },
+                .lazy = .{ .byte_abs = token_starts[parse_err.token] + extra_offset },
             },
             .msg = msg.toOwnedSlice(),
         };

src/main.zig

@@ -4040,13 +4040,14 @@ fn printErrMsgToStdErr(
         notes_len += 1;
     }
 
+    const extra_offset = tree.errorOffset(parse_error.tag, parse_error.token);
     const message: Compilation.AllErrors.Message = .{
         .src = .{
             .src_path = path,
             .msg = text,
-            .byte_offset = @intCast(u32, start_loc.line_start),
+            .byte_offset = @intCast(u32, start_loc.line_start) + extra_offset,
             .line = @intCast(u32, start_loc.line),
-            .column = @intCast(u32, start_loc.column),
+            .column = @intCast(u32, start_loc.column) + extra_offset,
             .source_line = source_line,
             .notes = notes_buffer[0..notes_len],
         },