Core support for AbsolutePath/FileInfo/DirectoryInfo and ITaskItem<T> as task parameters by baronfel · Pull Request #13971 · dotnet/msbuild

baronfel · 2026-06-05T19:42:12Z

Summary

Adds support for using AbsolutePath, System.IO.FileInfo, System.IO.DirectoryInfo, and ITaskItem (for path-like T) as MSBuild task input/output parameters, in addition to the existing string and ITaskItem types.

Changes

AbsolutePath: A new value type that wraps an absolute path string, validated via TaskEnvironment.GetAbsolutePath
FileInfo / DirectoryInfo: Paths are validated as absolute before creating the FileInfo/DirectoryInfo instance
ITaskItem<T>: A new generic interface allowing typed access to item specs, with T restricted to AbsolutePath, FileInfo, or DirectoryInfo in this PR
TaskItem<T>: Implementation of ITaskItem with mutable metadata backing
ValueTypeParser: Shared utility for parsing/formatting typed values (infrastructure for future PRs)
Task host serialization support for typed outputs
Full test coverage for all new parameter types

Stacked on

Base: main
Next: Add Roslyn analyzers (MSBuildTask0006/0007) to suggest typed task parameters #13972 (migration analyzers)

/cc @baronfel

…put parameters.

…etadata

The TASKHOST define is no longer set by any project in the main codebase since the .NET 3.5 taskhost was separated into a frozen project. These guards were always evaluating to true. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The out-of-proc task host gathers all [Output] properties and serializes them via TaskParameter. The PR's new AbsolutePath/FileInfo/DirectoryInfo outputs crashed the node: AbsolutePath (a struct) is never null so it always serialized, and Convert.ChangeType threw InvalidCastException because it is not IConvertible; FileInfo/DirectoryInfo additionally hit Assumed.Unreachable in the constructor. Route FileInfo/DirectoryInfo (scalar and array) to ValueType/ValueTypeArray, and convert values on the write side using ValueTypeParser.ToString - the same canonical conversion the in-process engine uses in TaskExecutionHost.GetValueOutputs - so in-proc and out-of-proc produce identical strings. Harden ValueTypeParser.ToString for a default AbsolutePath (null Value). The legacy net35 task host is intentionally untouched. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Unwrap TargetInvocationException in CreateTaskItemOfT so that parse errors from value-type constructors surface as the original exception (typically InvalidProjectFileException) rather than being wrapped in TargetInvocationException, which was swallowed by the outer catch. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

TaskItemData throws InvalidOperationException on all write operations (SetMetadata, RemoveMetadata, CopyMetadataTo). Switch the TaskItem<T>(T) constructor to use Utilities.TaskItem as the backing item, which supports full metadata mutation as expected by ITaskItem consumers. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

When constructing TaskItem<T> from an ITaskItem where T is FileInfo, DirectoryInfo, or AbsolutePath, prefer the FullPath metadata (which the MSBuild item system computes as an absolute rooted path) over ItemSpec, which may be a relative path. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Replace Value?.Equals(other.Value) with EqualityComparer<T>.Default.Equals to avoid boxing for value types, correctly handle null reference types, and use the appropriate comparer for each type T. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The code already correctly handles ITaskItem<T>[] for both input (IsValidVectorInputParameter) and output (IsAssignableToITaskItem), but had no explicit test coverage. Add tests for all four methods covering scalar and array ITaskItem<T> to prevent future regressions. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Treat arrays with ITaskItem-implementing element types as assignable outputs so TaskItem<T>[] follows the item-output path consistently with TaskExecutionHost behavior. Add unit tests covering TaskItem<int>[] assignability and output validity. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…nfo, DirectoryInfo) in PR1 Value-type T (int, bool, etc.) support for ITaskItem<T> will be added in a subsequent PR. Also remove ITaskItem<int> tests from PR1 test files. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Adds core infrastructure to support strongly-typed MSBuild task parameters and outputs for path-like values, including a new AbsolutePath-based flow, FileInfo/DirectoryInfo binding, and generic task items (ITaskItem<T> / TaskItem<T>). This primarily touches the task parameter binding pipeline (TaskExecutionHost), parameter type validation/serialization (TaskParameter*), and adds corresponding unit tests + docs updates.

Changes:

Introduces ITaskItem<T> (Framework) and TaskItem<T> (Utilities) to enable typed item identities.
Adds ValueTypeParser and switches task output serialization to a canonical string conversion path.
Extends TaskExecutionHost binding + unit tests to cover AbsolutePath, FileInfo/DirectoryInfo, and typed task items.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/Utilities/TaskItem_T.cs	New `TaskItem<T>` struct implementing typed task items over an `ITaskItem` backing instance.
src/Utilities.UnitTests/TaskItem_Tests.cs	Unit tests for `TaskItem<T>` metadata behavior and parsing behavior.
src/Tasks/Microsoft.Build.Tasks.csproj	Minor ItemGroup structure tweak.
src/Shared/ValueTypeParser.cs	New shared parser/formatter for value-like task parameter conversions.
src/Shared/UnitTests/TaskParameter_Tests.cs	Adds serialization tests for `AbsolutePath` / `FileInfo` / `DirectoryInfo`.
src/Shared/TaskParameterTypeVerifier.cs	Extends supported parameter types to include typed items and path-related types.
src/Shared/TaskParameter.cs	Updates value-type output serialization to use `ValueTypeParser` and support `FileInfo`/`DirectoryInfo`.
src/Framework/Microsoft.Build.Framework.csproj	Links `ValueTypeParser.cs` into Framework build.
src/Framework/ITaskItem_T.cs	New public `ITaskItem<T>` interface.
src/Build/Microsoft.Build.csproj	Adds Build → Utilities project reference (to use `TaskItem<T>`).
src/Build/BackEnd/TaskExecutionHost/TaskExecutionHost.cs	Adds parameter binding + output gathering support for typed path parameters and typed task items.
src/Build.UnitTests/BackEnd/TaskParameterTypeVerifier_Tests.cs	New tests covering typed parameter validation scenarios.
src/Build.UnitTests/BackEnd/TaskExecutionHost_Tests.cs	Expanded tests for new parameter types and typed task items.
src/Build.UnitTests/BackEnd/TaskBuilderTestTask.cs	Adds test task properties/outputs for new supported parameter types.
documentation/wiki/Tasks.md	Updates docs for supported task parameter types.

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Move TaskExecutionHost's duplicated path-like TaskItem<T>/ITaskItem<T> helper logic into TaskParameterTypeVerifier so type checks and typed item construction are centralized and reusable. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

baronfel · 2026-06-05T20:51:43Z

+        /// <summary>
+        /// A default <see cref="AbsolutePath"/> (null Value) must serialize cleanly. This is the
+        /// scenario that crashed the out-of-proc task host: a struct-typed output is never null, so
+        /// it always gets serialized, and the old code threw InvalidCastException because AbsolutePath
+        /// is not IConvertible. See https://github.com/dotnet/msbuild/pull/13016.
+        /// </summary>
+        [Fact]
+        public void DefaultAbsolutePathParameter()
+        {
+            TaskParameter t = new TaskParameter(default(AbsolutePath));
+
+            Assert.Equal(TaskParameterType.ValueType, t.ParameterType);
+
+            ((ITranslatable)t).Translate(TranslationHelpers.GetWriteTranslator());
+            TaskParameter t2 = TaskParameter.FactoryForDeserialization(TranslationHelpers.GetReadTranslator());
+
+            // A default AbsolutePath has a null Value and serializes to the empty string.
+            Assert.Equal(string.Empty, t2.WrappedParameter);
+            Assert.Equal(TaskParameterType.ValueType, t2.ParameterType);
+        }
+
+        [Fact]
+        public void AbsolutePathParameter()
+        {
+            string path = Path.Combine(Path.GetTempPath(), "TaskParameterTests_file.txt");
+            AbsolutePath value = new AbsolutePath(path);
+            TaskParameter t = new TaskParameter(value);
+
+            Assert.Equal(TaskParameterType.ValueType, t.ParameterType);
+
+            ((ITranslatable)t).Translate(TranslationHelpers.GetWriteTranslator());
+            TaskParameter t2 = TaskParameter.FactoryForDeserialization(TranslationHelpers.GetReadTranslator());
+
+            // Path types are serialized using the same canonical conversion as the in-process engine.
+            Assert.Equal(value.Value, t2.WrappedParameter);
+            Assert.Equal(TaskParameterType.ValueType, t2.ParameterType);
+        }
+
+        [Fact]
+        public void AbsolutePathArrayParameter()
+        {
+            AbsolutePath[] value = new AbsolutePath[]
+            {
+                new AbsolutePath(Path.Combine(Path.GetTempPath(), "a.txt")),
+                new AbsolutePath(Path.Combine(Path.GetTempPath(), "b.txt")),
+            };
+            TaskParameter t = new TaskParameter(value);
+
+            Assert.Equal(TaskParameterType.ValueTypeArray, t.ParameterType);
+
+            ((ITranslatable)t).Translate(TranslationHelpers.GetWriteTranslator());
+            TaskParameter t2 = TaskParameter.FactoryForDeserialization(TranslationHelpers.GetReadTranslator());
+
+            string[] stringArray = Assert.IsType<string[]>(t2.WrappedParameter);
+            Assert.Equal(value[0].Value, stringArray[0]);
+            Assert.Equal(value[1].Value, stringArray[1]);
+        }
+
+        [Fact]
+        public void FileInfoParameter()
+        {
+            FileInfo value = new FileInfo(Path.Combine(Path.GetTempPath(), "TaskParameterTests_file.txt"));
+            TaskParameter t = new TaskParameter(value);
+
+            Assert.Equal(TaskParameterType.ValueType, t.ParameterType);
+
+            ((ITranslatable)t).Translate(TranslationHelpers.GetWriteTranslator());
+            TaskParameter t2 = TaskParameter.FactoryForDeserialization(TranslationHelpers.GetReadTranslator());
+
+            // FileInfo is serialized as its full path, matching ValueTypeParser/the in-process engine.
+            Assert.Equal(value.FullName, t2.WrappedParameter);
+            Assert.Equal(TaskParameterType.ValueType, t2.ParameterType);
+        }
+
+        [Fact]
+        public void DirectoryInfoParameter()
+        {
+            DirectoryInfo value = new DirectoryInfo(Path.Combine(Path.GetTempPath(), "TaskParameterTests_dir"));
+            TaskParameter t = new TaskParameter(value);
+
+            Assert.Equal(TaskParameterType.ValueType, t.ParameterType);
+
+            ((ITranslatable)t).Translate(TranslationHelpers.GetWriteTranslator());
+            TaskParameter t2 = TaskParameter.FactoryForDeserialization(TranslationHelpers.GetReadTranslator());
+
+            Assert.Equal(value.FullName, t2.WrappedParameter);
+            Assert.Equal(TaskParameterType.ValueType, t2.ParameterType);
+        }
+
+        [Fact]
+        public void FileInfoArrayParameter()
+        {
+            FileInfo[] value = new FileInfo[]
+            {
+                new FileInfo(Path.Combine(Path.GetTempPath(), "a.txt")),
+                new FileInfo(Path.Combine(Path.GetTempPath(), "b.txt")),
+            };
+            TaskParameter t = new TaskParameter(value);
+
+            Assert.Equal(TaskParameterType.ValueTypeArray, t.ParameterType);
+
+            ((ITranslatable)t).Translate(TranslationHelpers.GetWriteTranslator());
+            TaskParameter t2 = TaskParameter.FactoryForDeserialization(TranslationHelpers.GetReadTranslator());
+
+            string[] stringArray = Assert.IsType<string[]>(t2.WrappedParameter);
+            Assert.Equal(value[0].FullName, stringArray[0]);
+            Assert.Equal(value[1].FullName, stringArray[1]);
+        }
+
+        [Fact]
+        public void DirectoryInfoArrayParameter()
+        {
+            DirectoryInfo[] value = new DirectoryInfo[]
+            {
+                new DirectoryInfo(Path.Combine(Path.GetTempPath(), "dirA")),
+                new DirectoryInfo(Path.Combine(Path.GetTempPath(), "dirB")),
+            };
+            TaskParameter t = new TaskParameter(value);
+
+            Assert.Equal(TaskParameterType.ValueTypeArray, t.ParameterType);
+
+            ((ITranslatable)t).Translate(TranslationHelpers.GetWriteTranslator());
+            TaskParameter t2 = TaskParameter.FactoryForDeserialization(TranslationHelpers.GetReadTranslator());
+
+            string[] stringArray = Assert.IsType<string[]>(t2.WrappedParameter);
+            Assert.Equal(value[0].FullName, stringArray[0]);
+            Assert.Equal(value[1].FullName, stringArray[1]);
+        }


This set of tests just confirms that the new types can be sent from TaskHosts to the main worker nodes.

baronfel · 2026-06-05T20:53:11Z

+    /// <summary>
+    /// Tests for TaskParameterTypeVerifier class
+    /// </summary>
+    public class TaskParameterTypeVerifier_Tests


these tests seem kind of low-quality to me but could be a safety net?

baronfel · 2026-06-05T20:54:34Z


        #endregion

+        #region AbsolutePath Params


These tests validate that actually using the new types as inputs/outputs results in the Test Task correctly receiving them and processing them.

baronfel and others added 12 commits June 5, 2026 14:31

support binding to AbsolutePath and AbsolutePath[] for task input/out…

a16fd89

…put parameters.

Allow users to bind to primitive types while still having access to m…

13a5f09

…etadata

Support FileInfo/DirectoryInfo parameter binding as well

53ff712

baronfel changed the title ~~typed params/core~~ Core support for AbsolutePath/FileInfo/DirectoryInfo and ITaskItem<T> as task parameters Jun 5, 2026

This was referenced Jun 5, 2026

Add Roslyn analyzers (MSBuildTask0006/0007) to suggest typed task parameters #13972

Draft

Expand ITaskItem<T> binding to support arbitrary value types (int, bool, etc.) #13974

Draft

baronfel marked this pull request as ready for review June 5, 2026 19:48

Copilot AI review requested due to automatic review settings June 5, 2026 19:48

Copilot started reviewing on behalf of baronfel June 5, 2026 19:49 View session

Copilot AI reviewed Jun 5, 2026

View reviewed changes

baronfel and others added 7 commits June 5, 2026 15:12

Potential fix for pull request finding

24e08e6

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Use existing boolean conversion helpers instead of reimplementing

151205f

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Update docs to align with parsed value types

371a3f9

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

actually escape set value in wrapped ITaskItem

94f0e25

fix potential nullrefs on uninitialized TaskItem<T> structs.

039b254

Unify task parameter helper logic across hosts

e19cd40

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

baronfel assigned jankratochvilcz Jun 5, 2026

Fix shared task-parameter helpers for TaskHost builds

e284e7a

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

baronfel commented Jun 6, 2026

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Core support for AbsolutePath/FileInfo/DirectoryInfo and ITaskItem<T> as task parameters#13971

Core support for AbsolutePath/FileInfo/DirectoryInfo and ITaskItem<T> as task parameters#13971
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baronfel commented Jun 5, 2026 •

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