25% smaller sourcemaps

src/bun.js/javascript.zig

@@ -115,6 +115,7 @@ pub const SavedSourceMap = struct {
     mutex: bun.Mutex = .{},
 
     pub const vlq_offset = 24;
+    const debug = bun.Output.scoped(.SourceMap, true);
 
     pub fn init(this: *SavedSourceMap, map: *HashTable) void {
         this.* = .{
@@ -240,7 +241,7 @@ pub const SavedSourceMap = struct {
 
     pub const HashTable = std.HashMap(u64, *anyopaque, IdentityContext(u64), 80);
 
-    pub fn onSourceMapChunk(this: *SavedSourceMap, chunk: SourceMap.Chunk, source: logger.Source) anyerror!void {
+    pub fn onSourceMapChunk(this: *SavedSourceMap, chunk: SourceMap.Chunk, source: *const logger.Source) anyerror!void {
         try this.putMappings(source, chunk.buffer);
     }
 
@@ -269,7 +270,8 @@ pub const SavedSourceMap = struct {
         this.map.deinit();
     }
 
-    pub fn putMappings(this: *SavedSourceMap, source: logger.Source, mappings: MutableString) !void {
+    pub fn putMappings(this: *SavedSourceMap, source: *const logger.Source, mappings: MutableString) !void {
+        debug("put {s} = {}", .{ source.path.text, bun.fmt.size(mappings.list.items.len, .{}) });
         try this.putValue(source.path.text, Value.init(bun.cast(*SavedMappings, mappings.list.items.ptr)));
     }
 
@@ -278,6 +280,7 @@ pub const SavedSourceMap = struct {
         defer this.unlock();
 
         const entry = try this.map.getOrPut(bun.hash(path));
+
         if (entry.found_existing) {
             var old_value = Value.from(entry.value_ptr.*);
             if (old_value.get(ParsedSourceMap)) |parsed_source_map| {
@@ -1056,7 +1059,7 @@ pub const VirtualMachine = struct {
         /// When the inspector is enabled, we want to generate an inline sourcemap.
         /// And, for now, we also store it in source_mappings like normal
         /// This is hideously expensive memory-wise...
-        pub fn onChunk(this: *SourceMapHandlerGetter, chunk: SourceMap.Chunk, source: logger.Source) anyerror!void {
+        pub fn onChunk(this: *SourceMapHandlerGetter, chunk: SourceMap.Chunk, source: *const logger.Source) anyerror!void {
             var temp_json_buffer = bun.MutableString.initEmpty(bun.default_allocator);
             defer temp_json_buffer.deinit();
             temp_json_buffer = try chunk.printSourceMapContentsAtOffset(source, temp_json_buffer, true, SavedSourceMap.vlq_offset, true);

src/bun.js/module_loader.zig

@@ -548,7 +548,7 @@ pub const RuntimeTranspilerStore = struct {
             }
 
             if (cache.entry) |*entry| {
-                vm.source_mappings.putMappings(parse_result.source, .{
+                vm.source_mappings.putMappings(&parse_result.source, .{
                     .list = .{ .items = @constCast(entry.sourcemap), .capacity = entry.sourcemap.len },
                     .allocator = bun.default_allocator,
                 }) catch {};
@@ -1787,7 +1787,7 @@ pub const ModuleLoader = struct {
                 }
 
                 if (cache.entry) |*entry| {
-                    jsc_vm.source_mappings.putMappings(parse_result.source, .{
+                    jsc_vm.source_mappings.putMappings(&parse_result.source, .{
                         .list = .{ .items = @constCast(entry.sourcemap), .capacity = entry.sourcemap.len },
                         .allocator = bun.default_allocator,
                     }) catch {};

src/js_printer.zig

@@ -420,14 +420,14 @@ pub const SourceMapHandler = struct {
     ctx: *anyopaque,
     callback: Callback,
 
-    const Callback = *const fn (*anyopaque, chunk: SourceMap.Chunk, source: logger.Source) anyerror!void;
-    pub fn onSourceMapChunk(self: *const @This(), chunk: SourceMap.Chunk, source: logger.Source) anyerror!void {
+    const Callback = *const fn (*anyopaque, chunk: SourceMap.Chunk, source: *const logger.Source) anyerror!void;
+    pub fn onSourceMapChunk(self: *const @This(), chunk: SourceMap.Chunk, source: *const logger.Source) anyerror!void {
         try self.callback(self.ctx, chunk, source);
     }
 
-    pub fn For(comptime Type: type, comptime handler: (fn (t: *Type, chunk: SourceMap.Chunk, source: logger.Source) anyerror!void)) type {
+    pub fn For(comptime Type: type, comptime handler: (fn (t: *Type, chunk: SourceMap.Chunk, source: *const logger.Source) anyerror!void)) type {
         return struct {
-            pub fn onChunk(self: *anyopaque, chunk: SourceMap.Chunk, source: logger.Source) anyerror!void {
+            pub fn onChunk(self: *anyopaque, chunk: SourceMap.Chunk, source: *const logger.Source) anyerror!void {
                 try handler(@as(*Type, @ptrCast(@alignCast(self))), chunk, source);
             }
 
@@ -454,6 +454,18 @@ pub const Options = struct {
     source_map_allocator: ?std.mem.Allocator = null,
     source_map_handler: ?SourceMapHandler = null,
     source_map_builder: ?*bun.sourcemap.Chunk.Builder = null,
+
+    // Necessary for the `source-map` library to work correctly, which means we
+    // only need it if we're generating source maps externally, such as when
+    // bundling or when the debugger is enabled.
+    //
+    // _tsc.js sourcemap size:
+    //
+    //    on: 3.18 MB
+    //   off: 2.49 MB
+    //
+    source_map_cover_lines_without_mappings: bool = true,
+
     css_import_behavior: Api.CssInJsBehavior = Api.CssInJsBehavior.facade,
     target: options.Target = .browser,
 
@@ -5848,7 +5860,7 @@ pub fn getSourceMapBuilder(
             opts.source_map_allocator orelse opts.allocator,
             is_bun_platform and generate_source_map == .lazy,
         ),
-        .cover_lines_without_mappings = true,
+        .cover_lines_without_mappings = opts.source_map_cover_lines_without_mappings,
         .approximate_input_line_count = tree.approximate_newline_count,
         .prepend_count = is_bun_platform and generate_source_map == .lazy,
         .line_offset_tables = opts.line_offset_tables orelse brk: {
@@ -6016,7 +6028,7 @@ pub fn printAst(
                 cache.put(printer.writer.ctx.getWritten(), source_maps_chunk.buffer.list.items);
             }
 
-            try handler.onSourceMapChunk(source_maps_chunk, source.*);
+            try handler.onSourceMapChunk(source_maps_chunk, source);
         } else {
             if (opts.runtime_transpiler_cache) |cache| {
                 cache.put(printer.writer.ctx.getWritten(), "");
@@ -6024,7 +6036,7 @@ pub fn printAst(
         }
     } else if (comptime generate_source_map) {
         if (opts.source_map_handler) |handler| {
-            try handler.onSourceMapChunk(printer.source_map_builder.generateChunk(printer.writer.ctx.getWritten()), source.*);
+            try handler.onSourceMapChunk(printer.source_map_builder.generateChunk(printer.writer.ctx.getWritten()), source);
         }
     }
 
@@ -6271,7 +6283,7 @@ pub fn printCommonJS(
 
     if (comptime generate_source_map) {
         if (opts.source_map_handler) |handler| {
-            try handler.onSourceMapChunk(printer.source_map_builder.generateChunk(printer.writer.ctx.getWritten()), source.*);
+            try handler.onSourceMapChunk(printer.source_map_builder.generateChunk(printer.writer.ctx.getWritten()), source);
         }
     }
 

src/sourcemap/sourcemap.zig

@@ -1226,7 +1226,7 @@ pub const Chunk = struct {
 
     pub fn printSourceMapContents(
         chunk: Chunk,
-        source: Logger.Source,
+        source: *const Logger.Source,
         mutable: MutableString,
         include_sources_contents: bool,
         comptime ascii_only: bool,
@@ -1243,7 +1243,7 @@ pub const Chunk = struct {
 
     pub fn printSourceMapContentsAtOffset(
         chunk: Chunk,
-        source: Logger.Source,
+        source: *const Logger.Source,
         mutable: MutableString,
         include_sources_contents: bool,
         offset: usize,

src/transpiler.zig

@@ -910,6 +910,12 @@ pub const Transpiler = struct {
                         .print_dce_annotations = transpiler.options.emit_dce_annotations,
                         .hmr_ref = ast.wrapper_ref,
                         .mangled_props = null,
+
+                        .source_map_cover_lines_without_mappings = if (is_bun)
+                            // If the sourcemaps are strictly for internal usage, we can disable this
+                            transpiler.options.debugger or transpiler.options.code_coverage or transpiler.options.dead_code_elimination == false
+                        else
+                            true,
                     },
                     enable_source_map,
                 ),