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Centralize exception ownership and fix exception unwinding to prevent leaks #551

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7b99007
Fix interpreter exception memory ownership
nbeerbower May 11, 2026
335029d
Fix compiled exception ownership leaks
nbeerbower May 11, 2026
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1 change: 1 addition & 0 deletions runtime/include/hemlock_runtime.h
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Original file line number Diff line number Diff line change
Expand Up @@ -493,6 +493,7 @@ typedef struct HmlExceptionContext {
HmlExceptionContext* hml_exception_push(void);
void hml_exception_pop(void);
__attribute__((noreturn)) void hml_throw(HmlValue exception_value);
__attribute__((noreturn)) void hml_throw_take(HmlValue exception_value);
HmlValue hml_exception_get_value(void);

// Runtime error helper - throws catchable exception with formatted message
Expand Down
2 changes: 1 addition & 1 deletion runtime/src/builtins_async.c
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Expand Up @@ -403,7 +403,7 @@ HmlValue hml_join(HmlValue task_val) {
// Re-throw task exception in the joining thread (parity with interpreter)
if (had_exception) {
hml_release(&result);
hml_throw(exception);
hml_throw_take(exception);
}

return result;
Expand Down
7 changes: 3 additions & 4 deletions runtime/src/builtins_core.c
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Expand Up @@ -169,6 +169,7 @@ HmlValue hml_get_args(void) {
for (int i = 0; i < g_argc; i++) {
HmlValue str = hml_val_string(g_argv[i]);
hml_array_push(arr, str);
hml_release(&str); // array_push retained its own reference
}

return arr;
Expand Down Expand Up @@ -821,13 +822,11 @@ HmlValue hml_parse_string_to_type(HmlValue val, HmlValueType target_type) {
void hml_assert(HmlValue condition, HmlValue message) {
if (!hml_to_bool(condition)) {
// Throw catchable exception (match interpreter behavior)
HmlValue exception_msg;
if (message.type == HML_VAL_STRING && message.as.as_string) {
exception_msg = message;
hml_throw(message); // borrowed argument
} else {
exception_msg = hml_val_string("assertion failed");
hml_throw_take(hml_val_string("assertion failed"));
}
hml_throw(exception_msg);
}
}

Expand Down
12 changes: 9 additions & 3 deletions runtime/src/builtins_func.c
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Expand Up @@ -30,20 +30,26 @@ void hml_exception_pop(void) {
}
}

void hml_throw(HmlValue exception_value) {
void hml_throw_take(HmlValue exception_value) {
if (!g_exception_stack || !g_exception_stack->is_active) {
// Uncaught exception
fprintf(stderr, "Uncaught exception: ");
print_value_to(stderr, exception_value);
fprintf(stderr, "\n");
hml_release(&exception_value);
exit(1);
}

hml_release(&g_exception_stack->exception_value);
g_exception_stack->exception_value = exception_value;
hml_retain(&g_exception_stack->exception_value);
longjmp(g_exception_stack->exception_buf, 1);
}

void hml_throw(HmlValue exception_value) {
hml_retain(&exception_value);
hml_throw_take(exception_value);
}

HmlValue hml_exception_get_value(void) {
if (g_exception_stack) {
HmlValue v = g_exception_stack->exception_value;
Expand All @@ -62,7 +68,7 @@ void hml_runtime_error(const char *format, ...) {
va_end(args);

HmlValue error_msg = hml_val_string(buffer);
hml_throw(error_msg);
hml_throw_take(error_msg);
}

// ========== DEFER SUPPORT ==========
Expand Down
68 changes: 34 additions & 34 deletions runtime/src/builtins_io.c
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Expand Up @@ -39,7 +39,7 @@ HmlValue hml_read_line(void) {

HmlValue hml_open(HmlValue path, HmlValue mode) {
if (path.type != HML_VAL_STRING) {
hml_throw(hml_val_string("open() expects string path"));
hml_throw_take(hml_val_string("open() expects string path"));
}

const char *path_str = path.as.as_string->data;
Expand All @@ -66,7 +66,7 @@ HmlValue hml_open(HmlValue path, HmlValue mode) {
char err_buf[512];
snprintf(err_buf, sizeof(err_buf), "Failed to open '%s' with mode '%s': %s",
path_str, mode_str, strerror(errno));
hml_throw(hml_val_string(err_buf));
hml_throw_take(hml_val_string(err_buf));
}

HmlFileHandle *fh = malloc(sizeof(HmlFileHandle));
Expand Down Expand Up @@ -99,7 +99,7 @@ static int hml_mode_to_open_flags(const char *mode) {
// open_fd(path, mode?) -> i32: open a file and return its raw POSIX fd.
HmlValue hml_open_fd(HmlValue path, HmlValue mode) {
if (path.type != HML_VAL_STRING) {
hml_throw(hml_val_string("open_fd() expects string path"));
hml_throw_take(hml_val_string("open_fd() expects string path"));
}

const char *path_str = path.as.as_string->data;
Expand All @@ -113,7 +113,7 @@ HmlValue hml_open_fd(HmlValue path, HmlValue mode) {
char err_buf[256];
snprintf(err_buf, sizeof(err_buf),
"open_fd() unsupported mode '%s' (use r, w, a, r+, w+, a+)", mode_str);
hml_throw(hml_val_string(err_buf));
hml_throw_take(hml_val_string(err_buf));
}

int is_write = (strchr(mode_str, 'w') != NULL || strchr(mode_str, 'a') != NULL ||
Expand All @@ -131,7 +131,7 @@ HmlValue hml_open_fd(HmlValue path, HmlValue mode) {
char err_buf[512];
snprintf(err_buf, sizeof(err_buf), "Failed to open '%s' with mode '%s': %s",
path_str, mode_str, strerror(errno));
hml_throw(hml_val_string(err_buf));
hml_throw_take(hml_val_string(err_buf));
}

return hml_val_i32(fd);
Expand All @@ -141,37 +141,37 @@ HmlValue hml_open_fd(HmlValue path, HmlValue mode) {
// file retains ownership of the fd; closing the file closes the fd.
HmlValue hml_fileno(HmlValue file) {
if (file.type != HML_VAL_FILE || !file.as.as_file) {
hml_throw(hml_val_string("fileno() expects file object"));
hml_throw_take(hml_val_string("fileno() expects file object"));
}

HmlFileHandle *fh = file.as.as_file;
if (fh->closed || !fh->fp) {
char err_buf[512];
snprintf(err_buf, sizeof(err_buf), "fileno() called on closed file '%s'",
fh->path ? fh->path : "<unknown>");
hml_throw(hml_val_string(err_buf));
hml_throw_take(hml_val_string(err_buf));
}

int fd = fileno((FILE*)fh->fp);
if (fd < 0) {
char err_buf[256];
snprintf(err_buf, sizeof(err_buf), "fileno() failed: %s", strerror(errno));
hml_throw(hml_val_string(err_buf));
hml_throw_take(hml_val_string(err_buf));
}

return hml_val_i32(fd);
}

HmlValue hml_file_read(HmlValue file, HmlValue size) {
if (file.type != HML_VAL_FILE) {
hml_throw(hml_val_string("read() expects file object"));
hml_throw_take(hml_val_string("read() expects file object"));
}

HmlFileHandle *fh = file.as.as_file;
if (fh->closed) {
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Cannot read from closed file '%s'", fh->path);
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}

int32_t read_size = 0;
Expand All @@ -195,14 +195,14 @@ HmlValue hml_file_read(HmlValue file, HmlValue size) {

HmlValue hml_file_read_all(HmlValue file) {
if (file.type != HML_VAL_FILE) {
hml_throw(hml_val_string("read() expects file object"));
hml_throw_take(hml_val_string("read() expects file object"));
}

HmlFileHandle *fh = file.as.as_file;
if (fh->closed) {
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Cannot read from closed file '%s'", fh->path);
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}

FILE *fp = (FILE*)fh->fp;
Expand All @@ -223,7 +223,7 @@ HmlValue hml_file_read_all(HmlValue file) {

char *buffer = malloc(size + 1);
if (!buffer) {
hml_throw(hml_val_string("Memory allocation failed"));
hml_throw_take(hml_val_string("Memory allocation failed"));
}
size_t bytes_read = fread(buffer, 1, size, fp);
buffer[bytes_read] = '\0';
Expand All @@ -237,7 +237,7 @@ HmlValue hml_file_read_all(HmlValue file) {
size_t total_read = 0;
char *buffer = malloc(capacity);
if (!buffer) {
hml_throw(hml_val_string("Memory allocation failed"));
hml_throw_take(hml_val_string("Memory allocation failed"));
}

while (1) {
Expand All @@ -247,7 +247,7 @@ HmlValue hml_file_read_all(HmlValue file) {
char *new_buffer = realloc(buffer, capacity);
if (!new_buffer) {
free(buffer);
hml_throw(hml_val_string("Memory allocation failed"));
hml_throw_take(hml_val_string("Memory allocation failed"));
}
buffer = new_buffer;
}
Expand All @@ -261,7 +261,7 @@ HmlValue hml_file_read_all(HmlValue file) {
free(buffer);
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Read error on file '%s'", fh->path);
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}
break; // EOF reached
}
Expand All @@ -277,14 +277,14 @@ HmlValue hml_file_read_all(HmlValue file) {

HmlValue hml_file_write(HmlValue file, HmlValue data) {
if (file.type != HML_VAL_FILE) {
hml_throw(hml_val_string("write() expects file object"));
hml_throw_take(hml_val_string("write() expects file object"));
}

HmlFileHandle *fh = file.as.as_file;
if (fh->closed) {
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Cannot write to closed file '%s'", fh->path);
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}

const char *str = "";
Expand All @@ -298,14 +298,14 @@ HmlValue hml_file_write(HmlValue file, HmlValue data) {

HmlValue hml_file_seek(HmlValue file, HmlValue position) {
if (file.type != HML_VAL_FILE) {
hml_throw(hml_val_string("seek() expects file object"));
hml_throw_take(hml_val_string("seek() expects file object"));
}

HmlFileHandle *fh = file.as.as_file;
if (fh->closed) {
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Cannot seek in closed file '%s'", fh->path);
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}

long pos = 0;
Expand All @@ -321,14 +321,14 @@ HmlValue hml_file_seek(HmlValue file, HmlValue position) {

HmlValue hml_file_tell(HmlValue file) {
if (file.type != HML_VAL_FILE) {
hml_throw(hml_val_string("tell() expects file object"));
hml_throw_take(hml_val_string("tell() expects file object"));
}

HmlFileHandle *fh = file.as.as_file;
if (fh->closed) {
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Cannot tell position in closed file '%s'", fh->path);
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}

return hml_val_i32((int32_t)ftell((FILE*)fh->fp));
Expand All @@ -348,14 +348,14 @@ void hml_file_close(HmlValue file) {

HmlValue hml_file_read_bytes(HmlValue file, HmlValue size) {
if (file.type != HML_VAL_FILE) {
hml_throw(hml_val_string("read_bytes() expects file object"));
hml_throw_take(hml_val_string("read_bytes() expects file object"));
}

HmlFileHandle *fh = file.as.as_file;
if (fh->closed) {
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Cannot read from closed file '%s'", fh->path);
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}

int32_t read_size = 0;
Expand All @@ -364,7 +364,7 @@ HmlValue hml_file_read_bytes(HmlValue file, HmlValue size) {
} else if (size.type == HML_VAL_I64) {
read_size = (int32_t)size.as.as_i64;
} else {
hml_throw(hml_val_string("read_bytes() expects integer size argument"));
hml_throw_take(hml_val_string("read_bytes() expects integer size argument"));
}

if (read_size <= 0) {
Expand All @@ -381,7 +381,7 @@ HmlValue hml_file_read_bytes(HmlValue file, HmlValue size) {

void *data = malloc(read_size);
if (!data) {
hml_throw(hml_val_string("Memory allocation failed in read_bytes()"));
hml_throw_take(hml_val_string("Memory allocation failed in read_bytes()"));
}

size_t bytes_read = fread(data, 1, read_size, (FILE*)fh->fp);
Expand All @@ -390,7 +390,7 @@ HmlValue hml_file_read_bytes(HmlValue file, HmlValue size) {
free(data);
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Read error on file '%s': %s", fh->path, strerror(errno));
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}

HmlBuffer *buf = calloc(1, sizeof(HmlBuffer));
Expand All @@ -406,25 +406,25 @@ HmlValue hml_file_read_bytes(HmlValue file, HmlValue size) {

HmlValue hml_file_write_bytes(HmlValue file, HmlValue data) {
if (file.type != HML_VAL_FILE) {
hml_throw(hml_val_string("write_bytes() expects file object"));
hml_throw_take(hml_val_string("write_bytes() expects file object"));
}

HmlFileHandle *fh = file.as.as_file;
if (fh->closed) {
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Cannot write to closed file '%s'", fh->path);
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}

// Check if file is writable
if (fh->mode[0] == 'r' && strchr(fh->mode, '+') == NULL) {
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Cannot write to file '%s' opened in read-only mode", fh->path);
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}

if (data.type != HML_VAL_BUFFER || !data.as.as_buffer) {
hml_throw(hml_val_string("write_bytes() expects buffer argument"));
hml_throw_take(hml_val_string("write_bytes() expects buffer argument"));
}

HmlBuffer *buf = data.as.as_buffer;
Expand All @@ -433,7 +433,7 @@ HmlValue hml_file_write_bytes(HmlValue file, HmlValue data) {
if (ferror((FILE*)fh->fp)) {
char _err_buf[512];
snprintf(_err_buf, sizeof(_err_buf), "Write error on file '%s': %s", fh->path, strerror(errno));
hml_throw(hml_val_string(_err_buf));
hml_throw_take(hml_val_string(_err_buf));
}

return hml_val_i32((int32_t)written);
Expand Down Expand Up @@ -964,15 +964,15 @@ HmlValue hml_is_dir(HmlValue path) {

HmlValue hml_file_stat(HmlValue path) {
if (path.type != HML_VAL_STRING || !path.as.as_string) {
hml_throw(hml_val_string("file_stat() requires a string path"));
hml_throw_take(hml_val_string("file_stat() requires a string path"));
}

struct stat st;
if (stat(path.as.as_string->data, &st) != 0) {
char err_buf[512];
snprintf(err_buf, sizeof(err_buf), "Failed to stat '%s': %s",
path.as.as_string->data, strerror(errno));
hml_throw(hml_val_string(err_buf));
hml_throw_take(hml_val_string(err_buf));
}

HmlValue obj = hml_val_object();
Expand Down
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