self-host: gen-c uses assert without #include <assert.h> in a module with no tests #6051

Profile (read first)

You are working as Gamma (Compiler Core) on epic #5980: rewrite t27c in t27 itself.
The self-hosted core (specs/compiler/core/t27core.t27, PR #6041) must write exactly the
bytes t27c gen-c writes, so every gen-c defect is a defect the core has to refuse instead of
learn. Fixing it here is what lets the core grow. Rules for this task:

• Change the Rust emitter only inside the Boundary below. gen/ is generated: never hand-edit it.
• Build with cargo build --release -p t27c and use ./target/release/t27c from the repository
  root, not a t27c on PATH.
• Write the regression test first and watch it fail on the unfixed compiler. Then fix, and
  revert the fix once to watch the test go red again. Say in the PR that you did both.
• Any other spec whose generated C changes must be listed in the PR by path, with one line on
  why the new bytes are right. A silent corpus change is a failed task.
• The PR body says Closes # plus this issue's number and Part of #5980. ASCII only in source files.

Context

A function that calls assert in a module with no test block compiles to C that calls assert without including <assert.h>, so a C99 compiler rejects it (call to undeclared function 'assert'). The self-hosted core refuses assert outside a tested module (E_CALL).

Reproduce

cargo build --release -p t27c
printf 'module m;\nfn f(x: i64) -> i64 {\n    assert(x > 0);\n    return x;\n}\n' > /tmp/asrt.t27
./target/release/t27c gen-c /tmp/asrt.t27

Today the relevant output is:

assert((x > 0));   <- no #include <assert.h> anywhere in the file

Original checks (kept for history; the Queen does not run these)

• 1. ./target/release/t27c gen-c /tmp/asrt.t27 | grep -c 'assert.h' prints at least 1 (today 0)
• 2. ./target/release/t27c gen-c /tmp/asrt.t27 > /tmp/asrt.c && cc -std=c99 -Werror=implicit-function-declaration -c -o /tmp/asrt.o /tmp/asrt.c; echo $? prints 0
• 3. cargo test --release -p t27c --test genc_assert_include passes

Original file list

• bootstrap/src/compiler.rs
• bootstrap/tests/genc_assert_include.rs

Original scenarios

• Given /tmp/asrt.t27 written by the Reproduce block,
  when ./target/release/t27c gen-c /tmp/asrt.t27 runs and its output is compiled with cc,
  then the file compiles under -std=c99 -Werror=implicit-function-declaration.

Original requirements

• FR-001: the include MUST follow the use of assert, not the presence of a test block.
• FR-900: cargo test --release -p t27c --test genc_assert_include MUST pass, and MUST fail with the fix reverted.
• FR-901: if bootstrap/tests/core_selfhost.rs exists on your base, cargo test --release -p t27c --test core_selfhost MUST still pass.

Queen-runnable restatement (2026-10-05)

The bee branch queen-6051 fixes bootstrap/src/compiler.rs and adds a Rust test, which the only-t27 rule refuses. Following specs/compiler/zig_test_shadowing.t27, the t27 part is a compiler rule spec that states when gen-c must include <assert.h>, with tests.

Boundary

• specs/compiler/c_assert_include.t27

User Scenarios & Testing

• Given master, where gen-c adds #include <assert.h> only when the module has a test block (compiler.rs, has_tests), when the rule spec lands, then t27c test-report runs its tests and they state that the include follows the use of assert.

Requirements

• FR-001: specs/compiler/c_assert_include.t27 MUST declare fn needs_assert_include(uses_assert: bool, has_test_block: bool) -> bool that returns true whenever uses_assert is true, whatever has_test_block is, and MUST carry at least 2 tests, one of them the defect case needs_assert_include(true, false) == true.
• FR-002: The change MUST NOT add or modify non-t27 hand-written code (specs/policy/own_language.t27).
• FR-003: A comment in the spec MUST name the reproduction from this issue (a function calling assert in a module with no test block) so the Rust fix can be checked against it later.

Success Criteria

• grep -c 'fn needs_assert_include' specs/compiler/c_assert_include.t27 prints 1
• grep -cE '^[[:space:]]*test ' specs/compiler/c_assert_include.t27 prints at least 2
• t27c test-report specs/compiler/c_assert_include.t27 2>&1 | grep -cE '^ (FAIL +0|pass +[1-9][0-9]*)$' prints 2