more flexible error reporting for SymbolResult

src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt

@@ -146,7 +146,9 @@ System.CommandLine
     public static LocalizationResources Instance { get; }
     public System.String ArgumentConversionCannotParse(System.String value, System.Type expectedType)
     public System.String ArgumentConversionCannotParseForCommand(System.String value, System.String commandAlias, System.Type expectedType)
+    public System.String ArgumentConversionCannotParseForCommand(System.String value, System.String commandAlias, System.Type expectedType, System.Collections.Generic.IEnumerable<System.String> completions)
     public System.String ArgumentConversionCannotParseForOption(System.String value, System.String optionAlias, System.Type expectedType)
+    public System.String ArgumentConversionCannotParseForOption(System.String value, System.String optionAlias, System.Type expectedType, System.Collections.Generic.IEnumerable<System.String> completions)
     public System.String DirectoryDoesNotExist(System.String path)
     public System.String ErrorReadingResponseFile(System.String filePath, System.IO.IOException e)
     public System.String ExceptionHandlerHeader()
@@ -386,6 +388,7 @@ System.CommandLine.IO
 System.CommandLine.Parsing
   public class ArgumentResult : SymbolResult
     public System.CommandLine.Argument Argument { get; }
+    public System.Void AddError(System.String errorMessage)
     public System.Object GetValueOrDefault()
     public T GetValueOrDefault<T>()
     public System.Void OnlyTake(System.Int32 numberOfTokens)
@@ -423,10 +426,10 @@ System.CommandLine.Parsing
     public static System.Threading.Tasks.Task<System.Int32> InvokeAsync(this Parser parser, System.String[] args, System.CommandLine.IConsole console = null, System.Threading.CancellationToken cancellationToken = null)
     public static System.CommandLine.ParseResult Parse(this Parser parser, System.String commandLine)
   public abstract class SymbolResult
-    public System.String ErrorMessage { get; set; }
     public System.CommandLine.LocalizationResources LocalizationResources { get; }
     public SymbolResult Parent { get; }
     public System.Collections.Generic.IReadOnlyList<Token> Tokens { get; }
+    public System.Void AddError(System.String errorMessage)
     public ArgumentResult FindResultFor(System.CommandLine.Argument argument)
     public CommandResult FindResultFor(System.CommandLine.Command command)
     public OptionResult FindResultFor(System.CommandLine.Option option)

src/System.CommandLine.NamingConventionBinder/ModelBinder.cs

@@ -132,7 +132,7 @@ private bool ShortCutTheBinding()
         var valueSource = GetValueSource(bindingSources, bindingContext, ValueDescriptor, EnforceExplicitBinding);
         return bindingContext.TryBindToScalarValue(ValueDescriptor,
                                                    valueSource,
-                                                   bindingContext.ParseResult.CommandResult.LocalizationResources,
+                                                   bindingContext.ParseResult,
                                                    out var boundValue)
                    ? (true, boundValue?.Value, true)
                    : (false, null, false);
@@ -277,7 +277,7 @@ internal static (BoundValue? boundValue, bool usedNonDefault) GetBoundValue(
         if (bindingContext.TryBindToScalarValue(
                 valueDescriptor,
                 valueSource,
-                bindingContext.ParseResult.CommandResult.LocalizationResources,
+                bindingContext.ParseResult,
                 out var boundValue))
         {
             return (boundValue, true);

src/System.CommandLine.Tests/ArgumentTests.cs

@@ -124,7 +124,7 @@ public void Validation_failure_message_can_be_specified_when_parsing_tokens()
             {
                 var argument = new Argument<FileSystemInfo>(result =>
                 {
-                    result.ErrorMessage = "oops!";
+                    result.AddError("oops!");
                     return null;
                 });
 
@@ -143,7 +143,7 @@ public void Validation_failure_message_can_be_specified_when_evaluating_default_
             {
                 var argument = new Argument<FileSystemInfo>(result =>
                 {
-                    result.ErrorMessage = "oops!";
+                    result.AddError("oops!");
                     return null;
                 }, true);
 
@@ -164,7 +164,7 @@ public void Validation_failure_message_can_be_specified_when_evaluating_default_
                     "-x",
                     result =>
                     {
-                        result.ErrorMessage = "oops!";
+                        result.AddError("oops!");
                         return null;
                     }, true);
 
@@ -389,15 +389,15 @@ public void Multiple_command_arguments_can_have_custom_parse_delegates()
                 {
                     new Argument<FileInfo[]>("from", argumentResult =>
                     {
-                        argumentResult.ErrorMessage = "nope";
+                        argumentResult.AddError("nope");
                         return null;
                     }, true)
                     {
                         Arity = new ArgumentArity(0, 2)
                     },
                     new Argument<DirectoryInfo>("to", argumentResult =>
                     {
-                        argumentResult.ErrorMessage = "UH UH";
+                        argumentResult.AddError("UH UH");
                         return null;
                     }, true)
                     {
@@ -426,7 +426,7 @@ public void When_custom_conversion_fails_then_an_option_does_not_accept_further_
                     new Argument<string>(),
                     new Option<string>("-x", argResult =>
                         {
-                            argResult.ErrorMessage = "nope";
+                            argResult.AddError("nope");
                             return default;
                         })
                 };
@@ -446,7 +446,7 @@ public void When_argument_cannot_be_parsed_as_the_specified_type_then_getting_va
                         return value;
                     }
 
-                    argumentResult.ErrorMessage = $"'{argumentResult.Tokens.Single().Value}' is not an integer";
+                    argumentResult.AddError($"'{argumentResult.Tokens.Single().Value}' is not an integer");
 
                     return default;
                 });

src/System.CommandLine.Tests/OptionTests.cs

@@ -287,11 +287,11 @@ public void Option_T_default_value_is_validated()
         {
             var option = new Option<int>("-x", () => 123);
             option.Validators.Add(symbol =>
-                                    symbol.ErrorMessage = symbol.Tokens
+                                    symbol.AddError(symbol.Tokens
                                                                 .Select(t => t.Value)
                                                                 .Where(v => v == "123")
                                                                 .Select(_ => "ERR")
-                                                                .FirstOrDefault());
+                                                                .First()));
 
             option
                 .Parse("-x 123")

src/System.CommandLine.Tests/ParseDiagramTests.cs

@@ -59,7 +59,7 @@ public void Parse_diagram_shows_type_conversion_errors()
 
             result.Diagram()
                   .Should()
-                  .Be($"[ {RootCommand.ExecutableName} [ -f !<not-an-int> ] ]");
+                  .Be($"[ {RootCommand.ExecutableName} ![ -f <not-an-int> ] ]");
         }
 
         [Fact]

src/System.CommandLine.Tests/ParsingValidationTests.cs

@@ -60,13 +60,17 @@ public void When_FromAmong_is_used_then_the_OptionResult_ErrorMessage_is_set()
 
             var parseResult = command.Parse("test --opt c");
 
-            parseResult.FindResultFor(option)
-                       .ErrorMessage
-                       .Should()
-                       .Be(parseResult.Errors.Single().Message)
-                       .And
-                       .Should()
-                       .NotBeNull();
+            var error = parseResult.Errors.Single();
+
+            error
+               .Message
+               .Should()
+               .Be(parseResult.CommandResult.LocalizationResources.UnrecognizedArgument("c", new []{ "a", "b"}));
+            error
+                .SymbolResult
+                .Should()
+                .BeOfType<OptionResult>();
+
         }
 
         [Fact] // https://github.com/dotnet/command-line-api/issues/1475
@@ -79,13 +83,16 @@ public void When_FromAmong_is_used_then_the_ArgumentResult_ErrorMessage_is_set()
 
             var parseResult = command.Parse("test c");
 
-            parseResult.FindResultFor(argument)
-                       .ErrorMessage
-                       .Should()
-                       .Be(parseResult.Errors.Single().Message)
-                       .And
-                       .Should()
-                       .NotBeNull();
+            var error = parseResult.Errors.Single();
+
+            error
+                .Message
+                .Should()
+                .Be(parseResult.CommandResult.LocalizationResources.UnrecognizedArgument("c", new []{ "a", "b"}));
+            error
+                .SymbolResult
+                .Should()
+                .BeOfType<ArgumentResult>();
         }
 
         [Fact] // https://github.com/dotnet/command-line-api/issues/1556
@@ -171,7 +178,7 @@ public void When_FromAmong_is_used_for_multiple_arguments_and_invalid_input_is_p
         }
 
         [Fact]
-        public void When_FromAmong_is_used_and_multiple_invalid_inputs_are_provided_the_error_mentions_first_invalid_argument()
+        public void When_FromAmong_is_used_and_multiple_invalid_inputs_are_provided_the_errors_mention_all_invalid_arguments()
         {
             Option<string[]> option = new(new[] { "--columns" });
             option.AcceptOnlyFromAmong("author", "language", "tags", "type");
@@ -185,12 +192,17 @@ public void When_FromAmong_is_used_and_multiple_invalid_inputs_are_provided_the_
 
             var result = command.Parse("list --columns c1 c2");
 
-            // Currently there is no possibility for a single validator to produce multiple errors,
-            // so only the first one is checked.
+            result.Errors.Count.Should().Be(2);
+
             result.Errors[0]
-                  .Message
-                  .Should()
-                  .Be(LocalizationResources.Instance.UnrecognizedArgument("c1", new[] { "author", "language", "tags", "type" }));
+                .Message
+                .Should()
+                .Be(LocalizationResources.Instance.UnrecognizedArgument("c1", new[] { "author", "language", "tags", "type" }));
+
+            result.Errors[1]
+                .Message
+                .Should()
+                .Be(LocalizationResources.Instance.UnrecognizedArgument("c2", new[] { "author", "language", "tags", "type" }));
         }
 
         [Fact]
@@ -334,7 +346,7 @@ public void A_custom_validator_can_be_added_to_a_command()
                 if (commandResult.Children.Any(sr => ((OptionResult)sr).Option.HasAlias("--one")) &&
                     commandResult.Children.Any(sr => ((OptionResult)sr).Option.HasAlias("--two")))
                 {
-                    commandResult.ErrorMessage = "Options '--one' and '--two' cannot be used together.";
+                    commandResult.AddError("Options '--one' and '--two' cannot be used together.");
                 }
             });
 
@@ -358,7 +370,7 @@ public void A_custom_validator_can_be_added_to_an_option()
             {
                 var value = r.GetValueOrDefault<int>();
 
-                r.ErrorMessage = $"Option {r.Token.Value} cannot be set to {value}";
+                r.AddError($"Option {r.Token.Value} cannot be set to {value}");
             });
 
             var command = new RootCommand { option };
@@ -385,7 +397,7 @@ public void A_custom_validator_can_be_added_to_an_argument()
             {
                 var value = r.GetValueOrDefault<int>();
 
-                r.ErrorMessage = $"Argument {r.Argument.Name} cannot be set to {value}";
+                r.AddError($"Argument {r.Argument.Name} cannot be set to {value}");
             });
 
             var command = new RootCommand { argument };
@@ -449,7 +461,7 @@ public void Validators_on_global_options_are_executed_when_invoking_a_subcommand
             var option = new Option<FileInfo>("--file");
             option.Validators.Add(r =>
             {
-                r.ErrorMessage = "Invoked validator";
+                r.AddError("Invoked validator");
             });
 
             var subCommand = new Command("subcommand");
@@ -484,7 +496,7 @@ public async Task A_custom_validator_added_to_a_global_option_is_checked(string
             var handlerWasCalled = false;
 
             var globalOption = new Option<int>("--value");
-            globalOption.Validators.Add(r => r.ErrorMessage = "oops!");
+            globalOption.Validators.Add(r => r.AddError("oops!"));
 
             var grandchildCommand = new Command("grandchild");
 
@@ -514,7 +526,7 @@ public void Custom_validator_error_messages_are_not_repeated()
         {
             var errorMessage = "that's not right...";
             var argument = new Argument<string>();
-            argument.Validators.Add(r => r.ErrorMessage = errorMessage);
+            argument.Validators.Add(r => r.AddError(errorMessage));
 
             var cmd = new Command("get")
             {
@@ -541,7 +553,7 @@ public void The_parsed_value_of_an_argument_is_available_within_a_validator()
 
                 if (value < 0 || value > 100)
                 {
-                    result.ErrorMessage = errorMessage;
+                    result.AddError(errorMessage);
                 }
             });
 
@@ -565,7 +577,7 @@ public void The_parsed_value_of_an_option_is_available_within_a_validator()
 
                 if (value < 0 || value > 100)
                 {
-                    result.ErrorMessage = errorMessage;
+                    result.AddError(errorMessage);
                 }
             });
 
@@ -1196,7 +1208,7 @@ public void Arity_failures_are_not_reported_for_both_an_argument_and_its_parent_
         public void Multiple_validators_on_the_same_command_do_not_report_duplicate_errors()
         {
             var command = new RootCommand();
-            command.Validators.Add(result => result.ErrorMessage = "Wrong");
+            command.Validators.Add(result => result.AddError("Wrong"));
             command.Validators.Add(_ => { });
 
             var parseResult = command.Parse("");
@@ -1214,7 +1226,7 @@ public void Multiple_validators_on_the_same_command_do_not_report_duplicate_erro
         public void Multiple_validators_on_the_same_option_do_not_report_duplicate_errors()
         {
             var option = new Option<string>("-x");
-            option.Validators.Add(result => result.ErrorMessage = "Wrong");
+            option.Validators.Add(result => result.AddError("Wrong"));
             option.Validators.Add(_ => { });
 
             var command = new RootCommand
@@ -1237,7 +1249,7 @@ public void Multiple_validators_on_the_same_option_do_not_report_duplicate_error
         public void Multiple_validators_on_the_same_argument_do_not_report_duplicate_errors()
         {
             var argument = new Argument<string>();
-            argument.Validators.Add(result => result.ErrorMessage = "Wrong");
+            argument.Validators.Add(result => result.AddError("Wrong"));
             argument.Validators.Add(_ => { });
 
             var command = new RootCommand
@@ -1262,7 +1274,7 @@ internal void When_there_is_an_arity_error_then_further_errors_are_not_reported(
             var option = new Option<string>("-o");
             option.Validators.Add(result =>
             {
-                result.ErrorMessage = "OOPS";
+                result.AddError("OOPS");
             }); //all good;
 
             var command = new Command("comm")

src/System.CommandLine/Argument.cs

@@ -107,6 +107,8 @@ private protected override string DefaultName
         /// </summary>
         public List<Action<ArgumentResult>> Validators => _validators ??= new ();
 
+        internal bool HasValidators => (_validators?.Count ?? 0) > 0;
+
         /// <summary>
         /// Gets the default value for the argument.
         /// </summary>