Fix CS2002 when EnableDefaultCompileItems=true in file-based apps

[Copilot]

Fix CS2002 Warning with EnableDefaultCompileItems in File-Based Apps ✅

Status: Complete and Verified

Problem Fixed

When EnableDefaultCompileItems=true was set in a file-based app (via #:property directive or Directory.Build.props), the main .cs file was included twice:

• Once explicitly via <Compile Include="file.cs" />
• Once implicitly via MSBuild's default compile item globbing

This caused CS2002 warning: "Source file specified multiple times"

Solution Implemented

• Modified VirtualProjectBuildingCommand.WriteProjectFile (line 1417)
• Added condition: <Compile Condition="'$(EnableDefaultCompileItems)' != 'true'" Include="{targetFilePath}" />
• Added comment explaining why the condition is needed
• Added issue link reference in test summaries
• Updated tests to use HaveStdOut instead of HaveStdOutContaining
• Updated all Api tests (Api(), Api_Diagnostic_01, Api_Diagnostic_02) with the new condition
• All tests pass successfully
• Manual verification completed for both scenarios
• Build succeeds with no warnings or errors
• Security scan (CodeQL) passed

Test Results

✅ Test 1: #:property EnableDefaultCompileItems=true - Works, no CS2002
✅ Test 2: Directory.Build.props with EnableDefaultCompileItems=true - Works, no CS2002
✅ Api tests: All updated and passing (Api, Api_Diagnostic_01, Api_Diagnostic_02)
✅ Unit tests: All passing
✅ SDK Build: Successful

Files Changed

1. src/Cli/dotnet/Commands/Run/VirtualProjectBuildingCommand.cs - Added condition with spaces, comment, and issue link
2. test/dotnet.Tests/CommandTests/Run/RunFileTests.cs - Updated tests with issue links, better assertions, and all Api_ test expectations

Fixes #51785

Original prompt

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This section details on the original issue you should resolve

<issue_title>Setting EnableDefaultCompileItems=True in a file-based app results in CS2002 as app file is included multiple times</issue_title>
<issue_description>If you set EnableDefaultCompileItems to true via a directive in a file-based app, in order to re-enable the default compilation items (like a regular project), you end up with a CS2002 warning being raised because the main file-based app .cs file is still explicitly included in the virtual project.

1. Add #:property EnableDefaultCompileItems=True to a file-based app
2. Build or run the file-based app
3. See CS2002 emitted for the app

We should consider conditioning the explicitly added compile item so that it's not added if EnableDefaultCompileItems is already true.</issue_description>

<agent_instructions>Let's avoid adding <Compile Include=""/> in file-based apps if EnableDefaultCompileItems is true. That can be set also in a Directory.Build.props file, not only as a #:property directive. Add tests for both cases. Hence we should probably do it at the msbuild level like <Compile Condition="'$(EnableDefaultCompileItems)'!='true'" Include=""/>.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Setting EnableDefaultCompileItems=True in a file-based app results in CS2002 as app file is included multiple times #51785

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[jjonescz]

@copilot

[Copilot]

Pull Request Overview

This PR fixes CS2002 warning ("Source file specified multiple times") that occurred when EnableDefaultCompileItems=true was set in file-based apps. The fix prevents the main .cs file from being included twice by adding a condition to the explicit <Compile> item.

• Conditionally excludes explicit <Compile> item when EnableDefaultCompileItems=true to avoid duplicate file inclusion
• Adds comprehensive test coverage for both directive-based and Directory.Build.props-based configuration scenarios
• Updates API test expectations to reflect the new conditional compile item

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Cli/dotnet/Commands/Run/VirtualProjectBuildingCommand.cs	Added MSBuild condition to <Compile> item to skip explicit inclusion when EnableDefaultCompileItems is true, with explanatory comment and issue reference
test/dotnet.Tests/CommandTests/Run/RunFileTests.cs	Updated existing test to verify fix via #:property directive, added new test for Directory.Build.props scenario, and updated API test expectations with the new condition