[wasm_builder] Lift import / definition restrictions.

Change-Id: Id0651e8e2ad270be5cc3788d361257769088faa6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/316627
Reviewed-by: Ömer Ağacan <[email protected]>
Commit-Queue: Joshua Litt <[email protected]>

Author: joshualitt

pkg/wasm_builder/lib/src/builder/builder.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import '../ir/ir.dart' as ir;
+
 export 'data_segments.dart' show DataSegmentBuilder, DataSegmentsBuilder;
 export 'exports.dart' show ExportsBuilder;
 export 'globals.dart' show GlobalsBuilder, GlobalBuilder;
@@ -20,3 +22,15 @@ mixin Builder<T> {
 
   T forceBuild();
 }
+
+// TODO(joshualitt): Share code when we have mixin composition.
+mixin IndexableBuilder<T> implements Builder<T>, ir.Indexable {
+  @override
+  T? _built;
+
+  @override
+  T build() => _built ??= forceBuild();
+
+  @override
+  T forceBuild();
+}

pkg/wasm_builder/lib/src/builder/function.dart

@@ -5,7 +5,8 @@
 part of 'functions.dart';
 
 /// A function defined in a module.
-class FunctionBuilder extends ir.BaseFunction with Builder<ir.DefinedFunction> {
+class FunctionBuilder extends ir.BaseFunction
+    with IndexableBuilder<ir.DefinedFunction> {
   /// All local variables defined in the function, including its inputs.
   List<ir.Local> get locals => body.locals;
 
@@ -26,8 +27,8 @@ class FunctionBuilder extends ir.BaseFunction with Builder<ir.DefinedFunction> {
 
   @override
   ir.DefinedFunction forceBuild() =>
-      ir.DefinedFunction(body.build(), index, type, functionName);
+      ir.DefinedFunction(body.build(), finalizableIndex, type, functionName);
 
   @override
-  String toString() => exportedName ?? "#$index";
+  String toString() => exportedName ?? "#$finalizableIndex";
 }

pkg/wasm_builder/lib/src/builder/functions.dart

@@ -4,6 +4,7 @@
 
 import '../ir/ir.dart' as ir;
 import 'builder.dart';
+import 'util.dart';
 
 part 'function.dart';
 
@@ -14,14 +15,10 @@ class FunctionsBuilder with Builder<ir.Functions> {
   final _functionBuilders = <FunctionBuilder>[];
   final _importedFunctions = <ir.Import>[];
   int _nameCount = 0;
-  bool _anyFunctionsDefined = false;
   ir.BaseFunction? _start;
 
   FunctionsBuilder(this._module);
 
-  /// This is guarded by [_anyFunctionsDefined].
-  int get _index => _importedFunctions.length + _functionBuilders.length;
-
   set start(ir.BaseFunction init) {
     assert(_start == null);
     _start = init;
@@ -39,8 +36,8 @@ class FunctionsBuilder with Builder<ir.Functions> {
   /// The [DefinedFunction.body] must be completed (including the terminating
   /// `end`) before the module can be serialized.
   FunctionBuilder define(ir.FunctionType type, [String? name]) {
-    _anyFunctionsDefined = true;
-    final function = FunctionBuilder(_module, _index, type, name);
+    final function =
+        FunctionBuilder(_module, ir.FinalizableIndex(), type, name);
     _functionBuilders.add(function);
     _addName(name, function);
     return function;
@@ -52,17 +49,18 @@ class FunctionsBuilder with Builder<ir.Functions> {
   /// using [FunctionsBuilder.define].
   ir.ImportedFunction import(String module, String name, ir.FunctionType type,
       [String? functionName]) {
-    if (_anyFunctionsDefined) {
-      throw "All function imports must be specified before any definitions.";
-    }
-    final function =
-        ir.ImportedFunction(module, name, _index, type, functionName);
+    final function = ir.ImportedFunction(
+        module, name, ir.FinalizableIndex(), type, functionName);
     _importedFunctions.add(function);
     _addName(functionName, function);
     return function;
   }
 
   @override
-  ir.Functions forceBuild() => ir.Functions(_start, _importedFunctions,
-      _functionBuilders.map((f) => f.build()).toList(), _functions, _nameCount);
+  ir.Functions forceBuild() {
+    final built = finalizeImportsAndBuilders<ir.DefinedFunction>(
+        _importedFunctions, _functionBuilders);
+    return ir.Functions(
+        _start, _importedFunctions, built, _functions, _nameCount);
+  }
 }

pkg/wasm_builder/lib/src/builder/global.dart

@@ -5,7 +5,7 @@
 part of 'globals.dart';
 
 /// A global variable defined in a module.
-class GlobalBuilder extends ir.Global with Builder<ir.DefinedGlobal> {
+class GlobalBuilder extends ir.Global with IndexableBuilder<ir.DefinedGlobal> {
   final InstructionsBuilder initializer;
 
   GlobalBuilder(ModuleBuilder module, super.index, super.type)
@@ -14,5 +14,5 @@ class GlobalBuilder extends ir.Global with Builder<ir.DefinedGlobal> {
 
   @override
   ir.DefinedGlobal forceBuild() =>
-      ir.DefinedGlobal(initializer.build(), index, type);
+      ir.DefinedGlobal(initializer.build(), finalizableIndex, type);
 }

pkg/wasm_builder/lib/src/builder/globals.dart

@@ -4,24 +4,20 @@
 
 import '../ir/ir.dart' as ir;
 import 'builder.dart';
+import 'util.dart';
 
 part 'global.dart';
 
 class GlobalsBuilder with Builder<ir.Globals> {
   final ModuleBuilder _module;
   final _importedGlobals = <ir.Import>[];
   final _globalBuilders = <GlobalBuilder>[];
-  bool _anyGlobalsDefined = false;
 
   GlobalsBuilder(this._module);
 
-  /// This is guarded by [_anyGlobalsDefined].
-  int get _index => _importedGlobals.length + _globalBuilders.length;
-
   /// Defines a new global variable in this module.
   GlobalBuilder define(ir.GlobalType type) {
-    _anyGlobalsDefined = true;
-    final global = GlobalBuilder(_module, _index, type);
+    final global = GlobalBuilder(_module, ir.FinalizableIndex(), type);
     _globalBuilders.add(global);
     return global;
   }
@@ -31,15 +27,15 @@ class GlobalsBuilder with Builder<ir.Globals> {
   /// All imported globals must be specified before any globals are declared
   /// using [Globals.define].
   ir.ImportedGlobal import(String module, String name, ir.GlobalType type) {
-    if (_anyGlobalsDefined) {
-      throw "All global imports must be specified before any definitions.";
-    }
-    final global = ir.ImportedGlobal(module, name, _index, type);
+    final global = ir.ImportedGlobal(module, name, ir.FinalizableIndex(), type);
     _importedGlobals.add(global);
     return global;
   }
 
   @override
-  ir.Globals forceBuild() => ir.Globals(
-      _importedGlobals, _globalBuilders.map((g) => g.build()).toList());
+  ir.Globals forceBuild() {
+    final built = finalizeImportsAndBuilders<ir.DefinedGlobal>(
+        _importedGlobals, _globalBuilders);
+    return ir.Globals(_importedGlobals, built);
+  }
 }