Unify function return lowering via emit_function_return for rvalue match arms.

Route diverging rvalue-match returns through scope_emit_return_unwind and goto epilogue, flip the regression test, regenerate text_summary.c, and note the fix in CHANGELOG and bug-hotspots.

Author: Cod-e-Codes

.cursor/skills/finding-ion-bugs/references/bug-hotspots.md

@@ -13,7 +13,7 @@ CLI errors use `TypeCheckError` Debug form (`UseAfterMove { ... }`). LSP reforma
 ## Codegen (`src/cgen/`)
 
 - Drop order and `ion_drop_*` for moved fields
-- **Return unwind**: statement `return` uses `scope_emit_return_unwind` in `generate_stmt` (`if`/`while`/`loop`/statement `match`/`unsafe`). Rvalue `match` diverging arms use `emit_match_arm_result_from_stmts`, which emits bare C `return` without unwind; confirmed by `rvalue_match_divergent_return_omits_owned_unwind` (tc rejects the shape in `test_match_arm_divergent_rvalue.ion`).
+- **Return unwind**: all function exits use `emit_function_return` (`ret_val`, `scope_emit_return_unwind`, `goto epilogue`), including diverging `return` inside rvalue `match` arms (`rvalue_match_divergent_return_unwinds_owned`). Value-producing rvalue arms still assign and `break` from the `switch`.
 - `Box`, `Vec`, `String` layout vs `runtime/ion_runtime.h`
 - Single-file merge (`merge_modules`) vs `--mode multi` divergences
 - `extern "C"` calls only inside `unsafe` blocks in source; cgen must not strip guards

CHANGELOG.md

@@ -9,7 +9,7 @@
 - **LSP**: diagnostics, hover, completion, go-to-definition; multi-error reporting; symbol table mirroring; diagnostics cleared on close; hover fixes for `let` bindings and module-qualified calls. Contiguous `//` doc comments attached to declarations (including `pub` items) for hover.
 - **Tooling**: GitHub Actions CI (Linux and Windows), pinned toolchain (1.96.0), `test_expectations.tsv` manifest, `--version`, line-numbered errors, Cursor agent skills. Split `tc` and `cgen` into submodules. `ion-build` driver and `ion.toml` manifests (`single`/`multi`, `out_dir`, `cflags`, `ldflags`, `stdlib_paths`, `emit_in_source`); per-example manifests and `build_hello`/`build_bad_main` harness smoke tests. Shared `discover_import_config` and stdlib search paths for `ion-compiler`, `ion-build`, and LSP. Integration harness precompiles `runtime/ion_runtime.c` once per run (`RUNTIME_OBJ`). `writing-ion-code` agent skill; `creating-ion-skills` examples index lists all eight project skills. Documented checked-in `examples/*.c` codegen snapshots in README and integration-test skill; regenerated example C output. Fixed `researching-pl-literature` skill `paper-seeds` reference formatting.
 - **Docs**: README, CONTRIBUTING, ION_SPEC, and agent skills aligned on project layout, `ion-build` workflow, `emit_in_source`, stdlib import order, LSP features and limitations, `src/build/` checklists, and portable Git Bash paths for `test_runner.sh`.
-- **Fixes**: match rvalue codegen, `Vec` struct drops, channel codegen, parser handling of `alias::call()`, scope-drop for moved-into-call bindings, HTTP server on Windows, integration harness on Windows. Cgen return-unwind: stop marking bindings dropped after inner-branch `return` (restores outer-path drops), dedupe `_`-prefixed unused silences, and mark call arguments moved at emission to avoid double-free on unwind. Integer indexing and `Vec<i32>` inference in the type checker. Match rvalue arms: reject diverging arms mixed with value arms; structural control-flow analysis for arm bodies (nested `if`/`else`, `loop` without `break`, `unsafe` blocks); reject mixed diverge and value-producing paths within one arm; cgen assigns through `if`/`else` value branches. `fmt::int_to_string` uses `String::push_byte` per digit instead of per-digit `push_str` branches; integration test asserts `0`, negatives, and `INT_MIN`. Clippy fix in `portable_source_label`.
+- **Fixes**: match rvalue codegen, `Vec` struct drops, channel codegen, parser handling of `alias::call()`, scope-drop for moved-into-call bindings, HTTP server on Windows, integration harness on Windows. Cgen return-unwind: stop marking bindings dropped after inner-branch `return` (restores outer-path drops), dedupe `_`-prefixed unused silences, mark call arguments moved at emission to avoid double-free on unwind, and unify all function returns via `emit_function_return` (including diverging rvalue `match` arms). Integer indexing and `Vec<i32>` inference in the type checker. Match rvalue arms: reject diverging arms mixed with value arms; structural control-flow analysis for arm bodies (nested `if`/`else`, `loop` without `break`, `unsafe` blocks); reject mixed diverge and value-producing paths within one arm; cgen assigns through `if`/`else` value branches. `fmt::int_to_string` uses `String::push_byte` per digit instead of per-digit `push_str` branches; integration test asserts `0`, negatives, and `INT_MIN`. Clippy fix in `portable_source_label`.
 - **Examples**: `text_summary` (fixture file), `data_lib` (multi-module), `channel_worker` (flat single-file). Per-example `*.toml` manifests for `ion-build`.
 - **Multi-file fixes**: merge private struct types for cross-module type checking; per-module C symbol prefixes in multi-file codegen (`io_print_int`); walk-up `runtime/` discovery for nested build directories. Integration tests `test_multi_struct`, `test_multi_fmt_io`. Example policy: single-file examples commit `.c` snapshots; `data_lib` multi-file keeps `.ion` only.
 

examples/text_summary/text_summary.c

@@ -40,18 +40,18 @@ static ION_MAYBE_UNUSED ReadResult ReadResult_Err_new(int arg0) {
     return result;
 }
 
+extern int write(int fd, uint8_t* buf, int count);
+
 extern int open(uint8_t* path, int flags);
 extern int read(int fd, uint8_t* buf, int count);
 extern int close(int fd);
 
-extern int write(int fd, uint8_t* buf, int count);
-
 TextCounts summarize_text(ion_string_t* ION_MAYBE_UNUSED text);
 int main(void);
-ReadResult fs_read_to_string_result(ion_string_t* ION_MAYBE_UNUSED path);
 void fmt_print_int(int ION_MAYBE_UNUSED n);
 void fmt_println_int(int ION_MAYBE_UNUSED n);
 ion_string_t* fmt_int_to_string(int ION_MAYBE_UNUSED n);
+ReadResult fs_read_to_string_result(ion_string_t* ION_MAYBE_UNUSED path);
 void io_print(ion_string_t* ION_MAYBE_UNUSED s);
 void io_println(ion_string_t* ION_MAYBE_UNUSED s);
 void io_print_str(uint8_t* ION_MAYBE_UNUSED s, int ION_MAYBE_UNUSED len);
@@ -122,46 +122,6 @@ int main(void) {
         return ret_val;
 }
 
-ReadResult fs_read_to_string_result(ion_string_t* ION_MAYBE_UNUSED path) {
-    ReadResult ret_val = {0};
-    {
-        int fd = open(path->data, 0);
-        if (fd < 0) {
-            ret_val = ReadResult_Err_new((-1));
-            if (path) { ion_string_free(path); }
-            goto epilogue;
-        }
-        ion_string_t* text = ion_string_new();
-        uint8_t buf[256] = {0};
-        int n = read(fd, &buf[0], 256);
-        while (n > 0) {
-            int i = 0;
-            while (i < n) {
-                ion_string_push_byte(text, (unsigned char)(buf[i]));
-                i = (i + 1);
-            }
-            n = read(fd, &buf[0], 256);
-        }
-        if (n < 0) {
-            int _closed = close(fd);
-            (void)_closed;
-            ret_val = ReadResult_Err_new((-2));
-            if (text) { ion_string_free(text); }
-            if (path) { ion_string_free(path); }
-            goto epilogue;
-        }
-        int _closed = close(fd);
-        (void)_closed;
-        ret_val = ReadResult_Ok_new(text);
-        if (path) { ion_string_free(path); }
-        goto epilogue;
-    }
-    if (path) { ion_string_free(path); }
-    goto epilogue;
-epilogue:
-        return ret_val;
-}
-
 void fmt_print_int(int ION_MAYBE_UNUSED n) {
     io_print_int(n);
     goto epilogue;
@@ -229,6 +189,46 @@ ion_string_t* fmt_int_to_string(int ION_MAYBE_UNUSED n) {
         return ret_val;
 }
 
+ReadResult fs_read_to_string_result(ion_string_t* ION_MAYBE_UNUSED path) {
+    ReadResult ret_val = {0};
+    {
+        int fd = open(path->data, 0);
+        if (fd < 0) {
+            ret_val = ReadResult_Err_new((-1));
+            if (path) { ion_string_free(path); }
+            goto epilogue;
+        }
+        ion_string_t* text = ion_string_new();
+        uint8_t buf[256] = {0};
+        int n = read(fd, &buf[0], 256);
+        while (n > 0) {
+            int i = 0;
+            while (i < n) {
+                ion_string_push_byte(text, (unsigned char)(buf[i]));
+                i = (i + 1);
+            }
+            n = read(fd, &buf[0], 256);
+        }
+        if (n < 0) {
+            int _closed = close(fd);
+            (void)_closed;
+            ret_val = ReadResult_Err_new((-2));
+            if (text) { ion_string_free(text); }
+            if (path) { ion_string_free(path); }
+            goto epilogue;
+        }
+        int _closed = close(fd);
+        (void)_closed;
+        ret_val = ReadResult_Ok_new(text);
+        if (path) { ion_string_free(path); }
+        goto epilogue;
+    }
+    if (path) { ion_string_free(path); }
+    goto epilogue;
+epilogue:
+        return ret_val;
+}
+
 void io_print(ion_string_t* ION_MAYBE_UNUSED s) {
     {
         int _result = write(1, s->data, (int)s->len);