## Summary
- Add `scan_module_decl()` — a lightweight preprocessor-based fallback
that resolves module declarations inside `#if`/`#ifdef` conditionals.
When `scan()` detects `need_preprocess=true`, this function runs clang's
preprocessor to evaluate conditions and extract the actual module name.
It stops lexing as soon as the module declaration is found, making it
much cheaper than `scan_precise()`.
- Integrate the fallback into `scan_dependency_graph()` for wave 0
source files, so conditional module declarations (e.g. `#ifdef
USE_MODULES / export module M; / #endif`) are correctly registered in
the dependency graph.
- Add comprehensive test cases covering all C++20 module declaration
forms from cppreference, including `scan_module_decl()` tests for
conditional resolution and `scan_precise()` tests for module import
semantics.
## Test plan
- [x] All 310 unit tests pass (0 failures, 9 skipped)
- [x] `scan()` tests cover: primary interface, implementation, dotted
names, partitions, GMF, conditional module declarations, private module
fragment
- [x] `scan_module_decl()` tests cover: basic, conditional with `-D`,
conditional with `#if` expression, GMF with conditional, implementation
unit, dotted name, partition, no-module file
- [x] `scan_precise()` tests cover: named import, multiple imports,
dotted import, partition import, export-import, export-import partition,
implementation import, GMF with import, mixed includes/imports,
no-module file
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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## Summary by CodeRabbit
* **New Features**
* Improved detection of module declarations hidden by conditional
compilation via a lightweight fallback scan. Resolved module vs.
interface classification is cached to avoid repeated work and is used
consistently in dependency mapping.
* Better handling and classification of module imports, partitions, and
global-fragment includes when building module relationships.
* **Tests**
* Added comprehensive unit tests covering module declaration extraction,
fallback resolution under preprocessor guards, imports, partitions,
includes, and macro-driven cases.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
