Task: Inventory prior work on extending C compilers

TASK-DESCRIPTION

• Create: documents/21-c-compiler-extensions-inventory.md
• Modify: c-compiler-extensions-inventory.md

Create documents/21-c-compiler-extensions-inventory.md. Place the research inventory produced during the fork-versus-extend investigation in the documents/ directory, where human-consumption documents belong, instead of the repository root. The content is an inventory of prior work on extending or modifying C compilers, covering: extensions already in mainstream compilers, real forked or modified C compilers, Objective-C as a frontend-plus-runtime precedent, attempts to add classes, methods, constructors, and RAII directly to C, compiler-fork maintenance burden, and Clang plugin limits. Record the provenance of the file and mark unverified claims explicitly. Correct the defer findings against primary sources: Clang documents -fdefer-ts in its released 22.1.0 and 23.1.0 command-line references, so Clang support is verified rather than unverified; GCC’s merge status remains unverified. Do not modify any other file; this task relocates and corrects only documents/21-c-compiler-extensions-inventory.md.

TASK-OUTPUT

Provide only the complete content of documents/21-c-compiler-extensions-inventory.md. No commentary.

TASK-CONTEXT

The inventory was produced by a research subagent at the repository root during the investigation of whether to extend an existing C compiler rather than build a fresh front end. The repository structure permits no root-level files other than README.md (see prompts/01-contract.md §7), and research documents belong in documents/ (see prompts/03-conventions.md §2). The decision this inventory feeds is documents/22-fork-or-extend-decision.md. Primary sources for the defer correction: https://releases.llvm.org/22.1.0/tools/clang/docs/ClangCommandLineReference.html and https://releases.llvm.org/23.1.0/tools/clang/docs/ClangCommandLineReference.html.

TASK-FILES

TASK-VERIFY

• Run: make test from the repository root.
• Expected: exit status 0.

OUTPUT: the content of documents/21-c-compiler-extensions-inventory.md, as TASK-OUTPUT describes, and nothing else.