iter 23.2.1: runtime/str.c with ail_str_eq + unconditional link

crates/ail/src/main.rs

@@ -1970,6 +1970,37 @@ fn locate_rc_runtime() -> Result<PathBuf> {
     )
 }
 
+/// Locate the workspace-root `runtime/str.c` file relative to the
+/// `ail` binary, mirroring [`locate_rc_runtime`]. Iter 23.2:
+/// `runtime/str.c` houses Str-runtime primitives (`ail_str_eq`,
+/// later `ail_str_compare`) and is linked unconditionally for every
+/// alloc strategy — `@ail_str_eq` is declared in the emitted IR
+/// header (codegen) without an alloc-strategy guard, so the symbol
+/// must always be resolvable at link time.
+fn locate_str_runtime() -> Result<PathBuf> {
+    let candidates = [
+        std::env::current_exe().ok(),
+        std::env::current_dir().ok(),
+    ];
+    for start in candidates.iter().flatten() {
+        let mut cur: &Path = start.as_path();
+        loop {
+            let candidate = cur.join("runtime").join("str.c");
+            if candidate.exists() {
+                return Ok(candidate);
+            }
+            match cur.parent() {
+                Some(p) => cur = p,
+                None => break,
+            }
+        }
+    }
+    anyhow::bail!(
+        "could not locate `runtime/str.c` (linked unconditionally). \
+         Run `ail` from inside the AILang workspace."
+    )
+}
+
 /// Iter 9b: shared build helper for `Cmd::Build` and `Cmd::Run`.
 /// Loads the workspace, runs the typechecker, emits IR, and links via
 /// clang. On typecheck failure, prints diagnostics to stderr and exits
@@ -2060,6 +2091,29 @@ fn build_to(
     let out_bin = out.unwrap_or_else(|| Path::new(".").join(&ws.entry).with_extension(""));
     let mut clang = std::process::Command::new("clang");
     clang.arg(opt).arg("-o").arg(&out_bin).arg(&ll_path);
+    // Iter 23.2: compile and link `runtime/str.c` unconditionally —
+    // `@ail_str_eq` is emitted in the IR header without an alloc-strategy
+    // guard (it backs the prelude `eq__Str` mono symbol). The .o is
+    // cached at <tmpdir>/str.o per build invocation; if a program never
+    // monomorphises `eq__Str`, clang -O2 dead-strips the symbol so the
+    // linker overhead is fixed and negligible.
+    let str_src = locate_str_runtime()?;
+    let str_obj = tmpdir.join("str.o");
+    let cstatus = std::process::Command::new("clang")
+        .arg("-O2")
+        .arg("-c")
+        .arg(&str_src)
+        .arg("-o")
+        .arg(&str_obj)
+        .status()
+        .context("compiling runtime/str.c")?;
+    if !cstatus.success() {
+        anyhow::bail!(
+            "clang failed compiling str.c (status {})",
+            cstatus
+        );
+    }
+    clang.arg(&str_obj);
     match alloc {
         ailang_codegen::AllocStrategy::Gc => {
             // Boehm conservative GC (Decision 9 / Iter 14f). The lowered
@@ -2139,6 +2193,17 @@ fn build_to(
 mod tests {
     use super::compose_merge_prose_prompt;
 
+    #[test]
+    fn locate_str_runtime_finds_workspace_str_c() {
+        let p = super::locate_str_runtime().expect("locate runtime/str.c");
+        assert!(
+            p.ends_with("runtime/str.c"),
+            "expected path ending in runtime/str.c, got {}",
+            p.display()
+        );
+        assert!(p.exists(), "located path must exist on disk: {}", p.display());
+    }
+
     /// The composed prompt must contain all three payloads
     /// byte-for-byte — the LLM has to see exactly what the user wrote,
     /// the original module's Form-A bytes, and the embedded spec, with

runtime/str.c

@@ -0,0 +1,26 @@
+/* AILang Str runtime primitives.
+ *
+ * Provides ABI-stable string operations against the existing
+ * constant-Str layout (NUL-terminated byte buffer, passed as
+ * `ptr` in LLVM IR). Lives separately from runtime/rc.c so that
+ * a future heap-Str ABI milestone can swap the implementations
+ * without touching the RC runtime.
+ *
+ * Linked unconditionally by `ail build` (Gc, Bump, Rc) so that
+ * any program that monomorphises `eq__Str` (auto-loaded from
+ * the prelude) finds the symbol. Programs that never call
+ * `eq` on Str leave @ail_str_eq as a dead-stripped no-op at
+ * link time under clang -O2.
+ */
+
+#include <stdbool.h>
+#include <string.h>
+
+/* Byte-equality on NUL-terminated strings. Mirrors strcmp(...) == 0
+ * but exposed under a stable AILang-namespaced ABI so the codegen
+ * caller does not assume libc's strcmp shape. Heap-Str ABI milestone
+ * will replace the body with length-prefixed comparison without
+ * changing the signature. */
+bool ail_str_eq(const char *a, const char *b) {
+    return strcmp(a, b) == 0;
+}