Add generated compile-time UI contracts

[lodyai]

Summary

This branch adds a generated Rust compile-time UI harness to resolve the
remaining Testing (Compile-Time / UI) warning from PR #79. It retains the
Python-generated project rejection tests for Makefile integration while
placing reviewed compiler, Clippy, and Rustdoc diagnostic contracts inside
each generated Rust project.

Review walkthrough

• Start with the Rust UI harness for the trybuild pass/fail flow and the Cargo-command fallback used for Clippy and Rustdoc.
• Review the generated UI fixtures for the supported case, representative lint failures, and checked-in expected diagnostics.
• Check the focused parent contract test for rendered-project execution with Rust and Rustdoc warnings denied.
• Finish with the contributor guidance and developer documentation for the diagnostic-review workflow and the reason trybuild cannot cover Clippy or Rustdoc directly.

Validation

• make check-fmt: passed; 31 files already formatted.
• make lint: passed with no warnings.
• make typecheck: passed; no issues in 31 source files.
• uvx --with pytest-copier --with pyyaml --with syrupy --with make-parser --with hypothesis pytest tests/test_template/test_compilation.py::test_generated_compile_time_ui_contracts -vv: passed; 1 test.
• make test: passed; 111 passed, 2 skipped, and 1 snapshot passed.
• make spelling: passed with typos 1.48.0.

Validation did not use TRYBUILD=overwrite, warning suppressions, or reduced
lint severities.

Notes

trybuild owns the compiler pass case and reviewed unsafe_code and
missing_docs .stderr files. The Rust integration harness invokes focused
Cargo commands for the Clippy and Rustdoc policies and compares their output
with narrow reviewed diagnostic fragments.

References

• Follow-up to Enforce injected environment access in generated Rust projects #79.
• Lody session

Summary by Sourcery

Add a generated Rust compile-time UI harness and fixtures to enforce lint and documentation diagnostic contracts in rendered projects.

New Features:

• Introduce a generated compile_ui.rs Rust test harness that runs trybuild, Clippy, and Rustdoc UI contracts.
• Add Rust UI case projects and fixtures, including compile-pass, compile-fail, and Cargo-based lint/doc examples with reviewed expected diagnostics.

Enhancements:

• Extend template developer and contributor documentation to describe the compile-time UI workflow, diagnostic review process, and TRYBUILD usage constraints.
• Update repository layout documentation to surface the new UI harness and fixture directories as part of the generated project structure.
• Strengthen policy-guidance tests to cover the new UI contracts and documentation expectations around compile-time diagnostics and TRYBUILD usage.

Build:

• Add trybuild as a dev-dependency in the Rust template Cargo manifest to support compile-time UI tests.

Tests:

• Add a Python template test that renders a project, validates the generated Rust UI harness and fixtures, and runs the compile-time UI test suite.
• Expand policy-guidance tests to assert inclusion of the new UI guidance in AGENTS and developer documentation.

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[sourcery-ai]

Reviewer's Guide

This PR adds a generated Rust compile-time UI harness and fixtures, wires them into the template Cargo config, and documents the lint/diagnostic contract and validation workflow while extending parent and policy tests to cover the new behaviour.

Sequence diagram for test_generated_compile_time_ui_contracts and Rust UI harness

sequenceDiagram
    actor Pytest
    participant PythonParentTests
    participant GeneratedProject
    participant RustUIHarness as tests_compile_ui_rs
    participant Trybuild
    participant CargoClippy
    participant CargoRustdoc

    Pytest->>PythonParentTests: test_generated_compile_time_ui_contracts
    PythonParentTests->>GeneratedProject: render_template_project
    PythonParentTests->>RustUIHarness: run_tests

    RustUIHarness->>Trybuild: run_supported_pass_fixture
    Trybuild-->>RustUIHarness: compiler_pass_ok

    RustUIHarness->>Trybuild: run_unsafe_code_compile_fail
    Trybuild-->>RustUIHarness: compare_unsafe_code_stderr

    RustUIHarness->>Trybuild: run_missing_docs_compile_fail
    Trybuild-->>RustUIHarness: compare_missing_docs_stderr

    RustUIHarness->>CargoClippy: cargo_clippy_ui_cases
    CargoClippy-->>RustUIHarness: output
    RustUIHarness->>RustUIHarness: compare_clippy_output_with_tests_ui_expected

    RustUIHarness->>CargoRustdoc: cargo_doc_ui_cases
    CargoRustdoc-->>RustUIHarness: output
    RustUIHarness->>RustUIHarness: compare_rustdoc_output_with_tests_ui_expected

    RustUIHarness-->>PythonParentTests: all_ui_contracts_pass
    PythonParentTests-->>Pytest: assert_success

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File-Level Changes

Change	Details	Files
Add a Rust UI harness that uses trybuild plus focused Cargo commands for Clippy and Rustdoc diagnostics.	Introduce tests/compile_ui.rs in the template that runs trybuild pass/fail cases and invokes cargo clippy/doc for curated UI fixtures. Define UiCase structs and CLIPPY_CASES/RUSTDOC_CASES arrays with embedded expected .stderr fragments via include_str!. Implement run_cargo_ui_case and assert_expected_failure helpers to execute Cargo commands, enforce failure, and assert that all reviewed diagnostic fragments are present.	template/tests/compile_ui.rs
Introduce generated UI fixtures and expected diagnostic files for compiler, Clippy, and Rustdoc lint contracts.	Add a dedicated UI fixtures Cargo package with lints configured to deny targeted Clippy and Rustdoc behaviours. Create pass-case and compile-fail Rust sources covering supported code, unsafe code, and missing docs, with adjacent .stderr files for trybuild. Add Clippy and Rustdoc UI binaries plus a feature-gated lib fixture that intentionally trigger specific diagnostics. Check in narrow expected diagnostic fragment files under tests/ui/expected/ for each Clippy/Rustdoc case.	template/tests/ui/cases/Cargo.toml template/tests/ui/pass/supported.rs template/tests/ui/cases/src/lib.rs template/tests/ui/cases/src/bin/rustdoc_invalid_codeblock_attributes.rs template/tests/ui/compile_fail/unsafe_code.rs template/tests/ui/cases/src/bin/clippy_missing_assert_message.rs template/tests/ui/cases/src/bin/rustdoc_bare_urls.rs template/tests/ui/cases/src/bin/rustdoc_invalid_html_tags.rs template/tests/ui/cases/src/bin/rustdoc_unescaped_backticks.rs template/tests/ui/compile_fail/missing_docs.rs template/tests/ui/cases/src/bin/clippy_disallowed_methods.rs template/tests/ui/cases/src/bin/rustdoc_broken_intra_doc_links.rs template/tests/ui/cases/src/bin/rustdoc_missing_crate_level_docs.rs template/tests/ui/compile_fail/missing_docs.stderr template/tests/ui/compile_fail/unsafe_code.stderr template/tests/ui/expected/clippy_disallowed_methods.stderr template/tests/ui/expected/clippy_missing_assert_message.stderr template/tests/ui/expected/rustdoc_bare_urls.stderr template/tests/ui/expected/rustdoc_broken_intra_doc_links.stderr template/tests/ui/expected/rustdoc_invalid_codeblock_attributes.stderr template/tests/ui/expected/rustdoc_invalid_html_tags.stderr template/tests/ui/expected/rustdoc_missing_crate_level_docs.stderr template/tests/ui/expected/rustdoc_private_intra_doc_links.stderr template/tests/ui/expected/rustdoc_unescaped_backticks.stderr
Wire trybuild as a dev-dependency into generated Cargo manifests.	Add a [dev-dependencies] section to the template Cargo.toml with a pinned trybuild version. Ensure generated projects have trybuild available for the compile_ui harness without extra manual setup.	template/Cargo.toml.jinja
Add a focused parent test that validates the generated compile-time UI contracts end-to-end.	Extend test_compilation.py with test_generated_compile_time_ui_contracts that renders a project, inspects the manifest and harness, and asserts presence of key UI fixtures and expected diagnostics. Use parse_toml_file in addition to read_generated_text to parse Cargo.toml and verify trybuild dev-dependency and harness content. Run the generated compile_ui test via cargo with RUSTFLAGS/RUSTDOCFLAGS that deny warnings.	tests/test_template/test_compilation.py
Update documentation and policy tests to describe and assert the new UI harness workflow and constraints.	Add a Compile-time UI tests section to the template developers guide explaining trybuild usage, Clippy/Rustdoc coverage limits, and TRYBUILD=overwrite rules. Update the concrete developers-guide.md to describe the fourth parent test and the non-overwrite policy for diagnostics. Extend repository-layout docs to list tests/compile_ui.rs and tests/ui/* directories and their roles. Update AGENTS.md guidance to cover trybuild .stderr review, non-use of TRYBUILD=overwrite in validation, and the division of responsibility between Python rejection tests and Rust UI harness. Expand policy-guidance tests to assert presence of the new documentation strings and references to test_generated_compile_time_ui_contracts and TRYBUILD policy.	template/docs/developers-guide.md.jinja docs/developers-guide.md template/docs/repository-layout.md.jinja template/AGENTS.md.jinja tests/test_template/test_policy_guidance.py

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[leynos]

Nah, that's just silly.