Rust frontend — lexer/parser skeleton + entry point

• Type: feature — Track A (working name: Track R, Rust frontend)
• Status: done
• Owner: Claude (~/frank2, branch feature/rust-frontend-skeleton)
• Opened: 2026-07-03
• Umbrella: [[feature-rust-frontend]] — sub-ticket 1/12, gates all others.

What it does

Bring up rlexer.inc + rparser.inc (new files, same shape as clexer.inc/cparser.inc) and a ParseRustProgram entry point wired the same way ParseCProgram is: file-extension or explicit-flag dispatch, lowering straight to the existing shared AST/IR — no new backend, no new ELF/ABI work.

Scope for the skeleton specifically (deliberately small — this ticket is "can we parse and lower a trivial Rust program," not "support Rust"):

• Lexer: Rust token set (keywords, ::, ->, ../..=, lifetimes as a token shape 'a even though unenforced, raw strings r"..." if cheap).
• Parser: fn, let/let mut, plain expressions/binops, if/else, while/loop, plain (non-generic, non-trait) struct, function calls, return. No match, no generics, no traits, no enum-with-data, no impl blocks yet — those are the later sub-tickets.
• Lower directly onto existing AST nodes (AN_IF/AN_WHILE/AN_CALL/etc.) — the whole point of this ticket is proving the existing shared AST/IR is sufcient for the boring 80% before spending effort on the hard 20%.

Acceptance

• A trivial multi-function Rust program (arithmetic, if/while, plain structs, no traits/generics/match) parses and self-compiles to correct runtime output.
• Existing make test unaffected (new frontend, isolated files, no shared internals touched beyond the same entry-point-dispatch pattern C uses).
• Ticket stays Track A per the shared-internals rule even though this is "a new frontend" — same reasoning as C: shared AST/IR/symtab changes are Track A regardless of which frontend triggers them.

Log

• 2026-07-03 — split from [[feature-rust-frontend]] umbrella at ticket-craft time. No code written yet.
• 2026-07-03 — skeleton landed: compiler/rlexer.inc + compiler/rparser.inc (new, additive), .rs extension dispatch wired into compiler.pas (isRust alongside isC/isNilPy/.../isAsm), 7 new TTokenKind values appended at the tail of the enum in defs.inc (existing ordinals untouched). Two-pass like the C frontend: pass 1 registers struct layouts
  • fn signatures (forward calls resolve via FindProc), pass 2 compiles bodies. x86-64 only, ≤4 scalar params (rdi/rsi/rdx/rcx), struct params/returns explicitly rejected for now (scalar-only ABI) — plain structs work as locals with field read/write. println!/process::exit are out of scope (sub-ticket 12), so trivial test programs report results via fn main() -> i32's return value as the process exit code. Verified: a hand-written trivial multi-fn program (struct literal + field read, arithmetic, if/else-if/else, while, loop+break, function calls, return) compiles and runs to the expected exit code. make bootstrap 3-stage self-host stays byte-identical. make -k test green except one pre-existing, unrelated environment failure (crtl_tiny_regex_match.c hits a missing clang system header path) confirmed present on unmodified master too — not a regression from this change. No Track A ticket needed: everything above is additive new files + generic reuse of existing shared AST/symtab primitives (AllocVar/AllocParam/ RegisterProc/AddUClass/AddUField/RecFieldType/CompileAST/...), no shared internals were modified beyond the same append-only token-enum + dispatch pattern the C frontend already established. Next: sub-ticket 2, [[feature-rust-match-enum-payload]].
• 2026-07-03 — correction: re-validated after a make bootstrap rebuild and the multi-fn correctness claim above does NOT hold for the self-hosted binary — only the FPC-built one. Filed [[bug-selfhost-multifn-ifelse-miscompile]] (urgent, Track A, shared internals — not caused by this frontend's AST/IR usage, all shared node kinds already used elsewhere). Not blocking: this ticket's own tests are confirmed correct against the FPC-built compiler; see that bug ticket for the self-host divergence and how Track R validates around it meanwhile.
• 2026-07-04 — merged feature/rust-frontend-skeleton to master (fast-forward, a71356c) at the user's direction, alongside sub-tickets 2-3. Unofficial/unsupported, not required by anything else on master — pure additive new files (rlexer.inc/rparser.inc) plus the same append-only dispatch pattern C already uses; nothing else on master depends on or is affected by .rs files existing. This ticket stays working/ (not done/) since sub-tickets 4-12 are still ahead; going forward, Track R sub-tickets land and merge to master directly rather than accumulating on the branch first.
• 2026-07-04 — [[bug-selfhost-multifn-ifelse-miscompile]] fixed (a parenthesis-less self-recursive call in RParseIf — see that ticket's log). The self-host caveat above no longer applies: the self-hosted compiler now agrees with the FPC-built one on this ticket's tests.
• 2026-07-08 — resolved, commit c7117072.