Always use LF line endings in scaffolded code - #39601

Fixes #29948

Code produced by dotnet ef dbcontext scaffold had mixed line endings on non-Windows platforms: the pre-processed T4 templates baked CRLF into their string literals, while WriteLine and the CSharpHelper fluent-chain/XML-comment output used Environment.NewLine. Blank lines (from WriteLine("")) were LF on Linux/macOS and everything else CRLF. This PR makes scaffolded code always use LF, on every platform, by emitting literal LF rather than parsing and replacing the output afterwards.

Changes

• Templates and pre-processed output: CSharpDbContextGenerator / CSharpEntityTypeGenerator (.tt and generated .cs) use literal LF. The base-class Environment.NewLine uses are replaced, and the templates no longer call WriteLine("") (it is implemented by the Mono template base class for custom templates and uses the platform newline); they use Write("\n") instead.
• CSharpHelper: Fragment (both overloads) and XmlComment now use a protected virtual NewLine (default Environment.NewLine) instead of IndentedStringBuilder. Output is identical under the default.
• ScaffoldingCSharpHelper: overrides NewLine to "\n". LfCSharpHelperServiceProvider substitutes it for the default ICSharpHelper for the templates, in both CSharpModelGenerator and TextTemplatingModelGenerator. A replaced or subclassed ICSharpHelper is left alone. Migrations, snapshots and compiled models keep using Environment.NewLine.
• Pinning: the four template files are eol=lf in .gitattributes and .editorconfig. This matters because the generated DbContext code contains a verbatim string (#warning ...) with a real line break whose value depends on the file's line endings. The PatchTemplate task in EFCore.Templates now writes LF, so the shipped .t4 files are LF regardless of the build machine.

Tests

• New end-to-end test that scaffolds a model (comments, fluent chains, many-to-many, sequence, index filter) with both CSharpModelGenerator and TextTemplatingModelGenerator, with and without data annotations, and asserts there is no \r.
• New CSharpHelper tests: exact LF output for the scaffolding helper, and a platform-independent test of the NewLine hook using a CRLF subclass.
• AssertFileContents (about 75 scaffolding tests) no longer ignores line-ending differences, and AssertContains no longer converts the expected text to Environment.NewLine.

Notes

• Behavior change: scaffolded files on Windows are now LF rather than CRLF. Re-scaffolding over CRLF files will rewrite every line.
• The generated .cs files were edited to match what the pre-processor emits, rather than regenerated, to avoid unrelated churn from a different pre-processor version. Regenerating in Visual Studio will bring Environment.NewLine back in the generated base class; the new tests catch that on Windows.
• Users' own custom .t4 templates keep whatever line endings the template file has.
• Not changed: CSharpRuntimeModelCodeGenerator (compiled models) and migrations.

🤖 Generated with Claude Code