Avoid mutation target collisions when embedded

- Added explicit status validation across error handling tests.
- Added lifecycle and slot-leak checks to older tests.
- Improved unhandled-error propagation coverage.
- Added repository guidance and a test runner script.
- Verified all 23 CTest tests pass.

Co-Authored by Codex GPT 5.4

AGENTS.md

@@ -0,0 +1,66 @@
+# Repository Guidelines
+
+## Project Structure & Module Organization
+
+This is a small C library built with CMake. Core implementation lives in
+`src/error.c`. The public header is generated at build time from
+`include/akerror.tmpl.h` by `scripts/generrno.sh`, which also generates
+`src/errno.c` under the build directory. CMake package and pkg-config templates
+are in `cmake/` and `akerror.pc.in`. Tests are one-file C programs in `tests/`;
+shared test helpers live beside them, such as `tests/err_capture.h`.
+
+## Build, Test, and Development Commands
+
+Use an out-of-tree build:
+
+```sh
+cmake -S . -B build
+cmake --build build
+ctest --test-dir build --output-on-failure
+```
+
+`cmake -S . -B build` configures the build and generates `akerror.h`.
+`cmake --build build` compiles `libakerror` and test executables. `ctest`
+runs the registered unit tests. To emit CI-style results, use:
+
+```sh
+ctest --test-dir build --output-on-failure --output-junit "$(pwd)/ctest-junit.xml"
+```
+
+Mutation testing is available through:
+
+```sh
+cmake --build build --target mutation
+scripts/mutation_test.py --target src/error.c --threshold 65
+```
+
+## Coding Style & Naming Conventions
+
+Use C99-compatible C and follow the surrounding style. Functions and types use
+the `akerr_` prefix; macros and constants use `AKERR_` or all-caps macro names
+such as `PREPARE_ERROR`. Keep generated-code changes in templates or generator
+scripts, not in build outputs. Preserve concise comments for invariants,
+macro constraints, and non-obvious error lifecycle behavior.
+
+## Testing Guidelines
+
+Add tests as `tests/err_<behavior>.c`. Register each new test in the
+`AKERR_TESTS` list in `CMakeLists.txt`; tests that intentionally abort must
+also be listed in `AKERR_WILL_FAIL_TESTS`. Prefer focused executable tests that
+return zero on success and use existing helpers such as `AKERR_CHECK`. Run the
+CTest suite before submitting changes, and run mutation testing when changing
+core control-flow, reference counting, stack-trace, or handler behavior.
+
+## Commit & Pull Request Guidelines
+
+Recent commits use short, imperative, sentence-case subjects, for example
+`Fix refcount leak and stack-trace buffer overflow`. Keep commits focused and
+describe the observable behavior changed. Pull requests should include a brief
+summary, tests run, and any compatibility impact for public macros, generated
+headers, installation paths, or CMake/pkg-config consumers.
+
+## Agent-Specific Instructions
+
+Do not overwrite uncommitted user changes. Avoid editing generated files in
+`build/`; update `include/akerror.tmpl.h`, `src/error.c`, CMake files, tests,
+or scripts instead.

CLAUDE.md

@@ -0,0 +1 @@
+See @AGENTS.md

CMakeLists.txt

@@ -67,6 +67,10 @@ set(AKERR_TESTS
     err_release_clears
     err_pool_exhaust
     err_maxval
+    err_refcount_double_fail
+    err_stacktrace_bounds
+    err_name_bounds
+    err_format_string
 )
 
 set(AKERR_WILL_FAIL_TESTS
@@ -95,9 +99,16 @@ set_tests_properties(
 # notices. This is a meta-check on the tests themselves, so it is a manual
 # target (it rebuilds and re-runs the whole suite many times), not a CTest test.
 #   cmake --build build --target mutation
+# When embedded in another project, use a namespaced target to avoid collisions
+# with mutation targets provided by sibling dependencies.
 find_package(Python3 COMPONENTS Interpreter)
 if(Python3_FOUND)
-    add_custom_target(mutation
+    if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+        set(AKERR_MUTATION_TARGET mutation)
+    else()
+        set(AKERR_MUTATION_TARGET akerror_mutation)
+    endif()
+    add_custom_target(${AKERR_MUTATION_TARGET}
         COMMAND ${Python3_EXECUTABLE}
                 ${CMAKE_CURRENT_SOURCE_DIR}/scripts/mutation_test.py
                 --source-root ${CMAKE_CURRENT_SOURCE_DIR}

README.md

@@ -210,6 +210,8 @@ ATTEMPT {
 
 This will assign the return value of the function in question to the akerr_ErrorContext previously prepared in the current scope. If the function returns an akerr_ErrorContext that indicates any type of error, the `ATTEMPT` block is immediately exited, and the `CLEANUP` block begins.
 
+(One caveat: because this exit is implemented with a C `break`, `CATCH` must not be used inside a loop within the `ATTEMPT` block — see the section "Important: do not use CATCH or FAIL_*_BREAK inside a loop" below.)
+
 ## Setting errors from functions or expressions returning integer
 
 For functions that return integer, such as logical comparisons or most standard library functions, use the `FAIL_ZERO_BREAK` and `FAIL_NONZERO_BREAK` macros. These macros allow you to capture an integer return code from an expression or function and set an error code in the current context based off that return.
@@ -232,6 +234,49 @@ ATTEMPT {
 
 When either of these two macros are used, the `ATTEMPT` block is immediately exited, and the `CLEANUP` block begins.
 
+## Important: do not use CATCH or FAIL_*_BREAK inside a loop
+
+`CATCH`, `FAIL_ZERO_BREAK`, `FAIL_NONZERO_BREAK`, and `FAIL_BREAK` leave the `ATTEMPT` block by executing a C `break` statement. In C, `break` only exits the *innermost* enclosing `for`, `while`, `do`, or `switch`. Therefore **these macros must not be used inside a loop (or a nested `switch`) that is itself inside an `ATTEMPT` block.** If you do, the `break` escapes only the loop — not the `ATTEMPT` — and the rest of the `ATTEMPT` body then runs with an error already pending:
+
+```c
+ATTEMPT {
+    for ( int i = 0; i < n; i++ ) {
+        CATCH(errctx, process(items[i]));   // WRONG: break exits the for loop, not the ATTEMPT
+    }
+    // ... this code still executes, with errctx already in an error state ...
+} CLEANUP {
+} PROCESS(errctx) {
+} FINISH(errctx, true);
+```
+
+Note that moving the loop into a helper function does **not** fix this on its own — if the helper still wraps the loop in an `ATTEMPT` and uses `CATCH`/`FAIL_*_BREAK` inside it, it has the exact same problem. The fix is to iterate with `return`-based macros, which are unaffected by loop nesting. Use one of the two patterns below.
+
+**Pattern 1 — use `PASS` (or a `FAIL_*_RETURN` macro) inside the loop.** These exit the *enclosing function* with a `return` rather than a `break`, so loop nesting is irrelevant. Use this when the loop should stop and propagate on the first error:
+
+```c
+akerr_ErrorContext AKERR_NOIGNORE *process_all(Item *items, int n)
+{
+    PREPARE_ERROR(errctx);
+    for ( int i = 0; i < n; i++ ) {
+        PASS(errctx, process(items[i]));   // returns from process_all on the first error
+    }
+    SUCCEED_RETURN(errctx);
+}
+```
+
+**Pattern 2 — move the loop into a helper and `CATCH` the single call.** When you need a `CLEANUP` block or want to `HANDLE` the error locally, put the loop in its own `akerr_ErrorContext *`-returning function (written per Pattern 1) and `CATCH` that one call. The `CATCH` is then not inside a loop, so its `break` scopes to the `ATTEMPT` correctly:
+
+```c
+ATTEMPT {
+    CATCH(errctx, process_all(items, n));   // a single CATCH, not looped
+} CLEANUP {
+    // ... always runs ...
+} PROCESS(errctx) {
+} HANDLE(errctx, AKERR_VALUE) {
+    // ... handle a failure from any iteration ...
+} FINISH(errctx, true);
+```
+
 # Passing errors
 
 Sometimes you can't actually do anything about the errors that come out of a given method, but you want that error to be propagated back up the call chain, and to be properly reported. If this is your goal, you can avoid using a `ATTEMPT ... FINISH` block, and simply use the `PASS` macro.

include/akerror.tmpl.h

@@ -110,8 +110,30 @@ void akerr_init_errno(void);
 	    akerr_log_method("%s:%s:%d: Unable to pull an error context from the array!", __FILE__, (char *)__func__, __LINE__); \
 	    exit(1);							\
 	}								\
+	__err_context->refcount += 1;					\
+    }
+
+/*
+ * Append a formatted line to the error's stack-trace buffer, bounded by the
+ * space that remains so a deep propagation chain cannot write past the end of
+ * stacktracebuf. snprintf reports the length it *would* have written, which on
+ * truncation exceeds what it actually wrote, so the cursor advance is clamped
+ * to the remaining space.
+ */
+#define AKERR_STACKTRACE_APPEND(__err_context, ...)			\
+    do {								\
+	char *__akerr_stb = (char *)__err_context->stacktracebuf;	\
+	size_t __akerr_used = (size_t)(__err_context->stacktracebufptr - __akerr_stb); \
+	if ( __akerr_used < AKERR_MAX_ERROR_STACKTRACE_BUF_LENGTH ) {	\
+	    size_t __akerr_rem = AKERR_MAX_ERROR_STACKTRACE_BUF_LENGTH - __akerr_used; \
+	    int __akerr_n = snprintf(__err_context->stacktracebufptr, __akerr_rem, __VA_ARGS__); \
+	    if ( __akerr_n < 0 ) {					\
+		__akerr_n = 0;						\
 	    }								\
-    __err_context->refcount += 1;
+	    __err_context->stacktracebufptr += ((size_t)__akerr_n < __akerr_rem) \
+		? (size_t)__akerr_n : (__akerr_rem - 1);		\
+	}								\
+    } while ( 0 )
 
 /*
  * Failure and success methods for functions that return akerr_ErrorContext *
@@ -168,11 +190,11 @@ void akerr_init_errno(void);
 #define FAIL(__err_context, __err, __message, ...)			\
     ENSURE_ERROR_READY(__err_context);					\
     __err_context->status = __err;					\
-    snprintf((char *)__err_context->fname, AKERR_MAX_ERROR_FNAME_LENGTH, __FILE__); \
-    snprintf((char *)__err_context->function, AKERR_MAX_ERROR_FUNCTION_LENGTH, __func__); \
+    snprintf((char *)__err_context->fname, AKERR_MAX_ERROR_FNAME_LENGTH, "%s", __FILE__); \
+    snprintf((char *)__err_context->function, AKERR_MAX_ERROR_FUNCTION_LENGTH, "%s", __func__); \
     __err_context->lineno = __LINE__;					\
     snprintf((char *)__err_context->message, AKERR_MAX_ERROR_CONTEXT_STRING_LENGTH, __message, ## __VA_ARGS__); \
-    __err_context->stacktracebufptr += snprintf(__err_context->stacktracebufptr, AKERR_MAX_ERROR_STACKTRACE_BUF_LENGTH, "%s:%s:%d: %d (%s) : %s\n", (char *)__err_context->fname, (char *)__err_context->function, __err_context->lineno, __err_context->status, akerr_name_for_status(__err_context->status, NULL), (__err_context->message == NULL ? "" : __err_context->message));
+    AKERR_STACKTRACE_APPEND(__err_context, "%s:%s:%d: %d (%s) : %s\n", (char *)__err_context->fname, (char *)__err_context->function, __err_context->lineno, __err_context->status, akerr_name_for_status(__err_context->status, NULL), (__err_context->message == NULL ? "" : __err_context->message));
 
 
 #define SUCCEED(__err_context)			\
@@ -198,7 +220,7 @@ void akerr_init_errno(void);
     VALID(__err_context, __stmt);					\
     if ( __err_context != NULL ) {					\
 	if ( __err_context->status != 0 ) {				\
-	    __err_context->stacktracebufptr += snprintf(__err_context->stacktracebufptr, AKERR_MAX_ERROR_STACKTRACE_BUF_LENGTH, "%s:%s:%d\n", (char *)__FILE__, (char *)__func__, __LINE__); \
+	    AKERR_STACKTRACE_APPEND(__err_context, "%s:%s:%d\n", (char *)__FILE__, (char *)__func__, __LINE__); \
 	    break;							\
 	}								\
     }

src/error.c

@@ -118,7 +118,7 @@ akerr_ErrorContext *akerr_release_error(akerr_ErrorContext *err)
 // Call with name = NULL to retrieve a status.
 char *akerr_name_for_status(int status, char *name)
 {
-    if ( status > AKERR_MAX_ERR_VALUE ) {
+    if ( status < 0 || status > AKERR_MAX_ERR_VALUE ) {
 	return "Unknown Error";
     }
     if ( name != NULL ) {

test.sh

@@ -0,0 +1,4 @@
+ cmake -S . -B build
+ cmake --build build
+ ctest --test-dir build --output-on-failure --output-junit "$(pwd)/ctest-junit.xml"
+ python3 scripts/mutation_test.py --target src/error.c --junit mutation-junit.xml --threshold 65

tests/err_break_variants.c

@@ -63,26 +63,26 @@ int main(void)
     akerr_ErrorContext *r;
 
     r = zero_break(0);
-    AKERR_CHECK(r != NULL && r->status == AKERR_VALUE);
+    AKERR_CHECK_STATUS(r, AKERR_VALUE);
     r = akerr_release_error(r);
     AKERR_CHECK(zero_break(7) == NULL);
 
     r = nonzero_break(7);
-    AKERR_CHECK(r != NULL && r->status == AKERR_INDEX);
+    AKERR_CHECK_STATUS(r, AKERR_INDEX);
     r = akerr_release_error(r);
     AKERR_CHECK(nonzero_break(0) == NULL);
 
     r = always_break();
-    AKERR_CHECK(r != NULL && r->status == AKERR_IO);
+    AKERR_CHECK_STATUS(r, AKERR_IO);
     r = akerr_release_error(r);
 
     r = zero_return(0);
-    AKERR_CHECK(r != NULL && r->status == AKERR_KEY);
+    AKERR_CHECK_STATUS(r, AKERR_KEY);
     r = akerr_release_error(r);
     AKERR_CHECK(zero_return(7) == NULL);
 
     r = nonzero_return(7);
-    AKERR_CHECK(r != NULL && r->status == AKERR_TYPE);
+    AKERR_CHECK_STATUS(r, AKERR_TYPE);
     r = akerr_release_error(r);
     AKERR_CHECK(nonzero_return(0) == NULL);
 

tests/err_capture.h

@@ -75,6 +75,12 @@ static int __attribute__((unused)) akerr_slots_in_use(void)
 	}							\
     } while ( 0 )
 
+#define AKERR_CHECK_STATUS(errctx, expected_status)			\
+    do {								\
+	AKERR_CHECK((errctx) != NULL);					\
+	AKERR_CHECK((errctx)->status == (expected_status));		\
+    } while ( 0 )
+
 #define AKERR_CHECK_CONTAINS(needle)				\
     AKERR_CHECK(strstr(akerr_capture_buf, (needle)) != NULL)
 

tests/err_catch.c

@@ -1,4 +1,5 @@
 #include "akerror.h"
+#include "err_capture.h"
 
 akerr_ErrorContext *func2(void)
 {
@@ -31,6 +32,11 @@ int main(void)
     } CLEANUP {
     } PROCESS(errctx) {
     } HANDLE(errctx, AKERR_NULLPOINTER) {
+        AKERR_CHECK_STATUS(errctx, AKERR_NULLPOINTER);
         akerr_log_method("Caught exception");
     } FINISH_NORETURN(errctx);
+
+    AKERR_CHECK(akerr_slots_in_use() == 0);
+    fprintf(stderr, "err_catch ok\n");
+    return 0;
 }

tests/err_cleanup.c

@@ -1,4 +1,5 @@
 #include "akerror.h"
+#include "err_capture.h"
 
 int x;
 
@@ -34,10 +35,15 @@ int main(void)
     } CLEANUP {
     } PROCESS(errctx) {
     } HANDLE(errctx, AKERR_NULLPOINTER) {
+	AKERR_CHECK_STATUS(errctx, AKERR_NULLPOINTER);
 	if ( x == 0 ) {
-	    fprintf(stderr, "Cleanup works\n");
-	    return 0;
-	}
+	    akerr_log_method("Cleanup works\n");
+	} else {
 	    return 1;
+	}
     } FINISH_NORETURN(errctx);
+
+    AKERR_CHECK(akerr_slots_in_use() == 0);
+    fprintf(stderr, "err_cleanup ok\n");
+    return 0;
 }

tests/err_errno.c

@@ -37,6 +37,7 @@ int main(void)
     } CLEANUP {
     } PROCESS(e) {
     } HANDLE(e, EACCES) {
+	AKERR_CHECK_STATUS(e, EACCES);
 	handled = 1;
     } FINISH_NORETURN(e);
 

tests/err_format_string.c

@@ -0,0 +1,34 @@
+#include "akerror.h"
+#include "err_capture.h"
+#include <string.h>
+
+/*
+ * FAIL records the source file and function names with snprintf. Those names
+ * must be passed as %s ARGUMENTS, not used as the format string -- otherwise a
+ * path containing a printf conversion (say a build directory with a '%') is
+ * interpreted as a format and reads nonexistent varargs (undefined behavior).
+ *
+ * #line lets us make __FILE__ contain a conversion specifier; the stored name
+ * must come back verbatim.
+ */
+
+#line 1 "pct%dname.c"
+akerr_ErrorContext *raise_with_percent_in_filename(void)
+{
+    PREPARE_ERROR(e);
+    FAIL_RETURN(e, AKERR_VALUE, "boom");
+}
+#line 22 "tests/err_format_string.c"
+
+int main(void)
+{
+    akerr_init();
+
+    akerr_ErrorContext *e = raise_with_percent_in_filename();
+    AKERR_CHECK(e != NULL);
+    AKERR_CHECK(strcmp(e->fname, "pct%dname.c") == 0);
+
+    e = akerr_release_error(e);
+    fprintf(stderr, "err_format_string ok\n");
+    return 0;
+}

tests/err_handle_default.c

@@ -8,6 +8,7 @@
 
 static int specific_fired = 0;
 static int default_fired = 0;
+static int default_status = 0;
 
 akerr_ErrorContext *boom(void)
 {
@@ -28,10 +29,12 @@ int main(void)
 	specific_fired = 1; /* must NOT run: error is AKERR_TYPE */
     } HANDLE_DEFAULT(e) {
 	default_fired = 1;
+	default_status = e->status;
     } FINISH_NORETURN(e);
 
     AKERR_CHECK(specific_fired == 0);
     AKERR_CHECK(default_fired == 1);
+    AKERR_CHECK(default_status == AKERR_TYPE);
     AKERR_CHECK(akerr_slots_in_use() == 0);
     fprintf(stderr, "err_handle_default ok\n");
     return 0;

tests/err_handle_dispatch.c

@@ -9,6 +9,7 @@
 static int a_fired = 0;
 static int b_fired = 0;
 static int c_fired = 0;
+static int b_status = 0;
 
 akerr_ErrorContext *boom(void)
 {
@@ -29,12 +30,14 @@ int main(void)
 	a_fired = 1;
     } HANDLE(e, AKERR_TYPE) {
 	b_fired = 1;
+	b_status = e->status;
     } HANDLE(e, AKERR_IO) {
 	c_fired = 1;
     } FINISH_NORETURN(e);
 
     AKERR_CHECK(a_fired == 0);
     AKERR_CHECK(b_fired == 1);
+    AKERR_CHECK(b_status == AKERR_TYPE);
     AKERR_CHECK(c_fired == 0);
     AKERR_CHECK(akerr_slots_in_use() == 0);
     fprintf(stderr, "err_handle_dispatch ok\n");

tests/err_handle_group.c

@@ -11,6 +11,8 @@
 
 static int group_fired = 0;
 static int other_fired = 0;
+static int group_status = 0;
+static int other_status = 0;
 
 akerr_ErrorContext *boom(int status)
 {
@@ -28,8 +30,10 @@ akerr_ErrorContext *run(int status)
     } HANDLE(e, AKERR_KEY)
 	  HANDLE_GROUP(e, AKERR_INDEX) {
 	group_fired++;
+	group_status = e->status;
     } HANDLE(e, AKERR_IO) {
 	other_fired++;
+	other_status = e->status;
     } FINISH(e, false);
     return e;
 }
@@ -40,15 +44,18 @@ int main(void)
 
     run(AKERR_KEY);
     AKERR_CHECK(group_fired == 1);
+    AKERR_CHECK(group_status == AKERR_KEY);
     AKERR_CHECK(other_fired == 0);
 
     run(AKERR_INDEX);
     AKERR_CHECK(group_fired == 2);
+    AKERR_CHECK(group_status == AKERR_INDEX);
     AKERR_CHECK(other_fired == 0);
 
     run(AKERR_IO);
     AKERR_CHECK(group_fired == 2);
     AKERR_CHECK(other_fired == 1);
+    AKERR_CHECK(other_status == AKERR_IO);
 
     AKERR_CHECK(akerr_slots_in_use() == 0);
     fprintf(stderr, "err_handle_group ok\n");

tests/err_name_bounds.c

@@ -0,0 +1,31 @@
+#include "akerror.h"
+#include "err_capture.h"
+#include <string.h>
+
+/*
+ * akerr_name_for_status must reject out-of-range status codes at BOTH ends.
+ * It already guarded the upper bound, but a negative status indexed
+ * __AKERR_ERROR_NAMES[negative] -- an out-of-bounds read (and an out-of-bounds
+ * write when a name is supplied). Every out-of-range status must return the
+ * "Unknown Error" sentinel instead.
+ */
+
+int main(void)
+{
+    akerr_init();
+
+    /* Below range. */
+    AKERR_CHECK(strcmp(akerr_name_for_status(-1, NULL), "Unknown Error") == 0);
+    AKERR_CHECK(strcmp(akerr_name_for_status(-9999, NULL), "Unknown Error") == 0);
+
+    /* Above range (already handled; kept as a guard against regressions). */
+    AKERR_CHECK(strcmp(akerr_name_for_status(AKERR_MAX_ERR_VALUE + 1, NULL),
+		       "Unknown Error") == 0);
+
+    /* A valid code must still resolve to its real name. */
+    AKERR_CHECK(strcmp(akerr_name_for_status(AKERR_NULLPOINTER, NULL),
+		       "Null Pointer Error") == 0);
+
+    fprintf(stderr, "err_name_bounds ok\n");
+    return 0;
+}

tests/err_pass.c

@@ -35,6 +35,7 @@ int main(void)
     } CLEANUP {
     } PROCESS(e) {
     } HANDLE(e, AKERR_IO) {
+	AKERR_CHECK_STATUS(e, AKERR_IO);
 	handled = 1;
     } FINISH_NORETURN(e);
 

tests/err_pool_refcount.c

@@ -11,6 +11,8 @@
 
 #define ITERATIONS 100000
 
+static int handled_status = 0;
+
 akerr_ErrorContext *boom(void)
 {
     PREPARE_ERROR(e);
@@ -31,6 +33,7 @@ akerr_ErrorContext *one_cycle(void)
     } CLEANUP {
     } PROCESS(e) {
     } HANDLE(e, AKERR_VALUE) {
+	handled_status = e->status;
     } FINISH(e, false);
     return e;
 }
@@ -42,7 +45,9 @@ int main(void)
     AKERR_CHECK(akerr_slots_in_use() == 0);
 
     for ( int iter = 0; iter < ITERATIONS; iter++ ) {
+	handled_status = 0;
 	(void)one_cycle();
+	AKERR_CHECK(handled_status == AKERR_VALUE);
     }
 
     AKERR_CHECK(akerr_slots_in_use() == 0);

tests/err_refcount_double_fail.c

@@ -0,0 +1,56 @@
+#include "akerror.h"
+#include "err_capture.h"
+
+/*
+ * Regression test for the refcount leak: ENSURE_ERROR_READY must increment
+ * refcount only when it *acquires* a fresh context, not on every FAIL/SUCCEED.
+ * A function that calls FAIL more than once on the same context and then
+ * propagates used to arrive at the caller with refcount 2; the caller released
+ * once, leaking the slot. After enough leaks the pool is exhausted and the
+ * library exit(1)s.
+ */
+
+static int handled_status = 0;
+
+akerr_ErrorContext *validate(void)
+{
+    PREPARE_ERROR(e);
+    ATTEMPT {
+	FAIL(e, AKERR_VALUE, "condition 1 failed");   /* acquires the context   */
+	FAIL(e, AKERR_KEY, "condition 2 failed");     /* must NOT re-acquire it  */
+    } CLEANUP {
+    } PROCESS(e) {
+    } FINISH(e, true);                                /* unhandled -> propagate  */
+    SUCCEED_RETURN(e);
+}
+
+/* One raise -> catch -> handle cycle; returns NULL (context released). */
+akerr_ErrorContext *one_cycle(void)
+{
+    PREPARE_ERROR(e);
+    ATTEMPT {
+	CATCH(e, validate());
+    } CLEANUP {
+    } PROCESS(e) {
+    } HANDLE(e, AKERR_KEY) {
+	handled_status = e->status;
+    } HANDLE(e, AKERR_VALUE) {
+    } FINISH(e, false);
+    return e;
+}
+
+int main(void)
+{
+    akerr_init();
+    AKERR_CHECK(akerr_slots_in_use() == 0);
+
+    for ( int i = 0; i < 32; i++ ) {
+	handled_status = 0;
+	(void)one_cycle();
+	AKERR_CHECK(handled_status == AKERR_KEY);
+    }
+
+    AKERR_CHECK(akerr_slots_in_use() == 0);
+    fprintf(stderr, "err_refcount_double_fail ok\n");
+    return 0;
+}

tests/err_release_clears.c

@@ -27,6 +27,7 @@ int main(void)
     } CLEANUP {
     } PROCESS(e) {
     } HANDLE(e, AKERR_VALUE) {
+	AKERR_CHECK_STATUS(e, AKERR_VALUE);
     } FINISH_NORETURN(e);
 
     AKERR_CHECK(e == NULL);

tests/err_stacktrace_bounds.c

@@ -0,0 +1,54 @@
+#include "akerror.h"
+#include "err_capture.h"
+#include <string.h>
+
+/*
+ * Regression test for the stack-trace buffer overflow. Each frame appended a
+ * line with snprintf, but passed the *full* buffer length as the size rather
+ * than the space remaining, and advanced the cursor by snprintf's would-be
+ * return value. A trace that filled the buffer therefore wrote past the end of
+ * stacktracebuf and ran the cursor out of bounds.
+ *
+ * We place a context in a struct with a guard region right after it, position
+ * the trace cursor near the end of the buffer, append one more frame, and
+ * require that nothing was written past the buffer and the cursor stayed in
+ * bounds.
+ */
+
+static struct {
+    akerr_ErrorContext ctx;
+    unsigned char guard[512];
+} probe;
+
+akerr_ErrorContext *append_frame(akerr_ErrorContext *e)
+{
+    FAIL_RETURN(e, AKERR_VALUE,
+		"an error message long enough to overflow a nearly full stack trace buffer");
+}
+
+int main(void)
+{
+    akerr_init();
+
+    memset(&probe, 0x00, sizeof(probe));
+    memset(probe.guard, 0xAA, sizeof(probe.guard));
+
+    akerr_ErrorContext *e = &probe.ctx;
+    e->refcount = 1;
+    /* Two bytes short of full: any real frame would overflow the old code. */
+    e->stacktracebufptr = probe.ctx.stacktracebuf
+	+ AKERR_MAX_ERROR_STACKTRACE_BUF_LENGTH - 2;
+
+    (void)append_frame(e);
+
+    /* Nothing may have been written past the end of stacktracebuf. */
+    for ( unsigned i = 0; i < sizeof(probe.guard); i++ ) {
+	AKERR_CHECK(probe.guard[i] == 0xAA);
+    }
+    /* The cursor must remain within the buffer. */
+    AKERR_CHECK(e->stacktracebufptr
+		<= probe.ctx.stacktracebuf + AKERR_MAX_ERROR_STACKTRACE_BUF_LENGTH);
+
+    fprintf(stderr, "err_stacktrace_bounds ok\n");
+    return 0;
+}

tests/err_swallow.c

@@ -9,6 +9,7 @@
  */
 
 static int wrong_handler_fired = 0;
+static int swallowed_status = 0;
 
 akerr_ErrorContext *boom(void)
 {
@@ -24,6 +25,7 @@ akerr_ErrorContext *swallow_it(void)
     ATTEMPT {
 	CATCH(e, boom());
     } CLEANUP {
+	swallowed_status = (e != NULL) ? e->status : 0;
     } PROCESS(e) {
     } HANDLE(e, AKERR_KEY) {
 	wrong_handler_fired = 1; /* does not match AKERR_VALUE */
@@ -38,6 +40,7 @@ int main(void)
     akerr_ErrorContext *res = swallow_it();
 
     AKERR_CHECK(wrong_handler_fired == 0);
+    AKERR_CHECK(swallowed_status == AKERR_VALUE);
     AKERR_CHECK(res == NULL); /* released even though unhandled */
     AKERR_CHECK(akerr_slots_in_use() == 0);
     fprintf(stderr, "err_swallow ok\n");

tests/err_trace.c

@@ -1,4 +1,10 @@
 #include "akerror.h"
+#include <stdlib.h>
+
+static void expect_unhandled_nullpointer(akerr_ErrorContext *errctx)
+{
+    exit((errctx != NULL && errctx->status == AKERR_NULLPOINTER) ? 1 : 0);
+}
 
 akerr_ErrorContext *func2(void)
 {
@@ -25,6 +31,9 @@ akerr_ErrorContext *func1(void)
 
 int main(void)
 {
+    akerr_init();
+    akerr_handler_unhandled_error = &expect_unhandled_nullpointer;
+
     PREPARE_ERROR(errctx);
     ATTEMPT {
 	CATCH(errctx, func1());