fix(extraction): detect a plain struct Derived : Base base clause in .h headers as C++ (#1592)

[colbymchenry]

Fixes #1592.

What was wrong

A .h header whose only C++ construct is a plain derived type —

struct Base {};
struct Derived : Base {};

— was classified as C. The .h language check (looksLikeCpp) recognizes class, namespace, template, access sections, virtual, using, and — since #1159/#1207 — the export-macro form struct ENGINE_API Derived : Base. The plain form has none of those signals. Routed through the C extractor, Derived vanished from the index and the base clause was read as a K&R-style declaration, minting a phantom function Base with returnType=Derived (the exact output in the issue).

A second, independent miss the reporter called out: the check only read the first 8192 characters, so a large header with a long C-compatible preamble (include guards, #defines, plain typedefs) hid the signal even when it was there.

What this does

looksLikeCpp() now runs two passes:

1. The existing 8 KB sample regex, unchanged.
2. A scan of the whole file (comments stripped) for a class/struct base clause: class/struct + tag + optional final + : + optional public/protected/private/virtual + a base name (scoped, optionally templated) followed by the body's { or a , introducing the next base.

That shape has no valid C reading, so widening it to the whole file can't drag a C header over to C++:

• a bit-field's : follows a member name inside the body (unsigned a : 3;), not the tag;
• a ternary's : is separated from the tag by ) / * / a declarator (sizeof(struct foo) : 0);
• a label or identifier like struct_end: has no whitespace after struct;
• comments are removed before the scan, so doc-comment prose (/* struct timeval: seconds, microseconds */) can't match; and the {/, terminator keeps a string literal's prose from matching too.

Detection only — the C++ extractor already handles the header correctly once it's routed there (renaming to .hpp, as the issue notes, already worked).

Tests

__tests__/extraction.test.ts:

• plain / : public Base / : ns::Base / : Base<int, Foo<T>> / final : Base / multi-base with { on the next line / : virtual Base → cpp;
• a base clause placed after 8192 characters of C-compatible preamble → cpp;
• controls that must stay c: a bit-field struct, sizeof(struct foo) : 0 + a cast ternary, a struct_end: label and struct_a identifiers, doc-comment prose shaped like a base clause, and the two pre-existing C controls;
• end-to-end extractFromSource('src/min.h', …) on the issue's header: a struct node Derived (language cpp), exactly one Base node and it is a struct — no phantom function.

Issue repro re-run against this build: codegraph init → query Derived returns the cpp struct; query Base returns only the struct; the files table records src/min.h as cpp.

Full suite: npm test → 174 files passed, 3010 tests passed, 179 skipped.

🤖 Generated with Claude Code

https://claude.ai/code/session_01LxZj6W6Y1SHXwvpT3uwJpK