Add some more @useResult to parser constructors.

lib/src/debug/profile.dart

@@ -1,3 +1,5 @@
+import 'package:meta/meta.dart';
+
 import '../core/parser.dart';
 import '../parser/action/continuation.dart';
 import '../reflection/transform.dart';
@@ -24,6 +26,7 @@ import '../shared/types.dart';
 ///
 /// The optional [output] callback can be used to receive [ProfileFrame]
 /// objects with the full profiling information at the end of the parse.
+@useResult
 Parser<T> profile<T>(Parser<T> root,
     {VoidCallback<ProfileFrame> output = print, Predicate<Parser>? predicate}) {
   final frames = <ProfileFrame>[];

lib/src/debug/progress.dart

@@ -1,3 +1,5 @@
+import 'package:meta/meta.dart';
+
 import '../context/context.dart';
 import '../core/parser.dart';
 import '../parser/action/continuation.dart';
@@ -27,6 +29,7 @@ import '../shared/types.dart';
 ///
 /// The optional [output] callback can be used to continuously receive
 /// [ProgressFrame] updates with the current progress information.
+@useResult
 Parser<T> progress<T>(Parser<T> root,
     {VoidCallback<ProgressFrame> output = print,
     Predicate<Parser>? predicate}) {

lib/src/debug/trace.dart

@@ -1,3 +1,5 @@
+import 'package:meta/meta.dart';
+
 import '../context/context.dart';
 import '../context/result.dart';
 import '../core/parser.dart';
@@ -32,6 +34,7 @@ import '../shared/types.dart';
 ///
 /// The optional [output] callback can be used to continuously receive
 /// [TraceEvent] objects with current enter and exit data.
+@useResult
 Parser<T> trace<T>(Parser<T> root,
     {VoidCallback<TraceEvent> output = print, Predicate<Parser>? predicate}) {
   TraceEvent? parent;

lib/src/definition/grammar.dart

@@ -71,6 +71,7 @@ abstract class GrammarDefinition<R> {
   /// The optional [start] reference specifies a different starting production
   /// into the grammar. The optional [arguments] list parametrizes the called
   /// production.
+  @useResult
   Parser<T> build<T>({Function? start, List<Object> arguments = const []}) {
     if (start != null) {
       return resolve(Function.apply(start, arguments));

lib/src/definition/reference.dart

@@ -1,3 +1,5 @@
+import 'package:meta/meta.dart';
+
 import '../core/parser.dart';
 import 'internal/reference.dart';
 import 'internal/undefined.dart';
@@ -11,6 +13,7 @@ import 'resolve.dart';
 /// using one of the strongly typed alternatives [ref0], [ref1], [ref2], ...
 /// instead.
 @Deprecated('Use [ref0], [ref1], [ref2], ... instead.')
+@useResult
 Parser<T> ref<T>(
   Function function, [
   dynamic arg1 = undefined,
@@ -37,12 +40,14 @@ Parser<T> ref<T>(
 ///
 /// If you function takes arguments, consider one of the typed alternatives
 /// [ref1], [ref2], [ref3], ... instead.
+@useResult
 Parser<T> ref0<T>(Parser<T> Function() function) =>
     ReferenceParser<T>(function, const []);
 
 /// Reference to a production [function] parametrized with 1 argument.
 ///
 /// See [ref0] for a detailed description.
+@useResult
 Parser<T> ref1<T, A1>(
   Parser<T> Function(A1) function,
   A1 arg1,
@@ -52,6 +57,7 @@ Parser<T> ref1<T, A1>(
 /// Reference to a production [function] parametrized with 2 arguments.
 ///
 /// See [ref0] for a detailed description.
+@useResult
 Parser<T> ref2<T, A1, A2>(
   Parser<T> Function(A1, A2) function,
   A1 arg1,
@@ -62,6 +68,7 @@ Parser<T> ref2<T, A1, A2>(
 /// Reference to a production [function] parametrized with 3 arguments.
 ///
 /// See [ref0] for a detailed description.
+@useResult
 Parser<T> ref3<T, A1, A2, A3>(
   Parser<T> Function(A1, A2, A3) function,
   A1 arg1,
@@ -73,6 +80,7 @@ Parser<T> ref3<T, A1, A2, A3>(
 /// Reference to a production [function] parametrized with 4 arguments.
 ///
 /// See [ref0] for a detailed description.
+@useResult
 Parser<T> ref4<T, A1, A2, A3, A4>(
   Parser<T> Function(A1, A2, A3, A4) function,
   A1 arg1,
@@ -85,6 +93,7 @@ Parser<T> ref4<T, A1, A2, A3, A4>(
 /// Reference to a production [function] parametrized with 5 arguments.
 ///
 /// See [ref0] for a detailed description.
+@useResult
 Parser<T> ref5<T, A1, A2, A3, A4, A5>(
   Parser<T> Function(A1, A2, A3, A4, A5) function,
   A1 arg1,
@@ -98,6 +107,7 @@ Parser<T> ref5<T, A1, A2, A3, A4, A5>(
 /// Reference to a production [function] parametrized with 6 arguments.
 ///
 /// See [ref0] for a detailed description.
+@useResult
 Parser<T> ref6<T, A1, A2, A3, A4, A5, A6>(
   Parser<T> Function(A1, A2, A3, A4, A5, A6) function,
   A1 arg1,
@@ -112,6 +122,7 @@ Parser<T> ref6<T, A1, A2, A3, A4, A5, A6>(
 /// Reference to a production [function] parametrized with 7 arguments.
 ///
 /// See [ref0] for a detailed description.
+@useResult
 Parser<T> ref7<T, A1, A2, A3, A4, A5, A6, A7>(
   Parser<T> Function(A1, A2, A3, A4, A5, A6, A7) function,
   A1 arg1,
@@ -127,6 +138,7 @@ Parser<T> ref7<T, A1, A2, A3, A4, A5, A6, A7>(
 /// Reference to a production [function] parametrized with 8 arguments.
 ///
 /// See [ref0] for a detailed description.
+@useResult
 Parser<T> ref8<T, A1, A2, A3, A4, A5, A6, A7, A8>(
   Parser<T> Function(A1, A2, A3, A4, A5, A6, A7, A8) function,
   A1 arg1,
@@ -144,6 +156,7 @@ Parser<T> ref8<T, A1, A2, A3, A4, A5, A6, A7, A8>(
 /// Reference to a production [function] parametrized with 9 arguments.
 ///
 /// See [ref0] for a detailed description.
+@useResult
 Parser<T> ref9<T, A1, A2, A3, A4, A5, A6, A7, A8, A9>(
   Parser<T> Function(A1, A2, A3, A4, A5, A6, A7, A8, A9) function,
   A1 arg1,

lib/src/expression/builder.dart

@@ -1,3 +1,5 @@
+import 'package:meta/meta.dart';
+
 import '../core/parser.dart';
 import '../definition/resolve.dart';
 import '../parser/combinator/settable.dart';
@@ -65,13 +67,15 @@ class ExpressionBuilder<T> {
   final SettableParser<T> _loopback = undefined();
 
   /// Creates a new group of operators that share the same priority.
+  @useResult
   ExpressionGroup<T> group() {
     final group = ExpressionGroup<T>(_loopback);
     _groups.add(group);
     return group;
   }
 
   /// Builds the expression parser.
+  @useResult
   Parser<T> build() {
     final parser = _groups.fold<Parser<T>>(
       failure('Highest priority group should define a primitive parser.'),

lib/src/reflection/optimize.dart

@@ -1,8 +1,11 @@
+import 'package:meta/meta.dart';
+
 import '../core/parser.dart';
 import '../parser/combinator/settable.dart';
 import 'transform.dart';
 
 /// Returns a copy of [parser] with all settable parsers removed.
+@useResult
 @Deprecated('Use `resolve(Parser)` instead.')
 Parser<T> removeSettables<T>(Parser<T> parser) {
   return transformParser(parser, <R>(each) {
@@ -14,6 +17,7 @@ Parser<T> removeSettables<T>(Parser<T> parser) {
 }
 
 /// Returns a copy of [parser] with all duplicates parsers collapsed.
+@useResult
 Parser<T> removeDuplicates<T>(Parser<T> parser) {
   final uniques = <Parser>{};
   return transformParser(parser, <R>(source) {

lib/src/reflection/transform.dart

@@ -1,3 +1,5 @@
+import 'package:meta/meta.dart';
+
 import '../core/parser.dart';
 import 'iterable.dart';
 
@@ -10,6 +12,7 @@ typedef TransformationHandler = Parser<T> Function<T>(Parser<T> parser);
 /// The implementation first creates a copy of each parser reachable in the
 /// input grammar; then the resulting grammar is traversed until all references
 /// to old parsers are replaced with the transformed ones.
+@useResult
 Parser<T> transformParser<T>(Parser<T> parser, TransformationHandler handler) {
   final mapping = Map<Parser, Parser>.identity();
   for (final each in allParser(parser)) {