[release/10.0.3xx] File-based apps: ensure shebang analyzer only applies to #:include

[jjonescz]

Backport of #54397.

Description

Ensures that a new analyzer (CA2266) introduced in 10.0.300 only applies to new scenarios to avoid a breaking change. This analyzer was always about #:include directives (a feature of file-based apps that was also introduced in 10.0.300) but it was implemented in such a way that it also applied to file-based apps that somehow included .cs files in other ways than via #:include - for example via <Compile> items imported through custom SDKs or msbuild targets from nuget packages.

Customer impact

Reported by a customer on GitHub - #53749 (comment).

Regression

I guess yes since it can break people's builds.

Risk

Low. Scoped change. Unit test coverage.

[Copilot]

Pull request overview

This backport updates the CA2266 “missing shebang” analyzer behavior for file-based apps so it only triggers when the entry-point file uses #:include, avoiding warnings for multi-file compilations created via other mechanisms (e.g., extra Compile items from MSBuild props).

Changes:

• Update CSharpMissingShebangInFileBasedProgram to require a #:include directive (and no shebang) before reporting CA2266.
• Expand/adjust CLI integration tests to cover Directory.Build.props extra Compile items vs real #:include, including non-.cs includes.
• Update analyzer unit tests to align with the new triggering condition and reduce duplicated solution-transform code.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
test/dotnet.Tests/CommandTests/Run/RunFileTests.cs	Adjusts and adds file-based dotnet run tests to ensure CA2266 only fires for #:include (including non-.cs includes).
src/Microsoft.CodeAnalysis.NetAnalyzers/tests/Microsoft.CodeAnalysis.NetAnalyzers.UnitTests/Microsoft.NetCore.Analyzers/Usage/MissingShebangInFileBasedProgramTests.cs	Updates analyzer unit tests to require #:include for CA2266 and adds a “multiple files without include” coverage case.
src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.CSharp.NetAnalyzers/Microsoft.NetCore.Analyzers/Usage/CSharpMissingShebangInFileBasedProgram.cs	Changes analyzer logic to look for an #:include directive in leading trivia before reporting CA2266.
src/Cli/dotnet/Commands/Run/CSharpCompilerCommand.Generated.cs	Updates the generated template header comment (but currently references a test name that doesn’t exist in this branch).

[jjonescz]

@RikkiGibson @333fred for a sign off on a backport, thanks