Test ignored-error storage across translation units

CMakeLists.txt

@@ -282,6 +282,22 @@ foreach(_test IN LISTS AKERR_TESTS)
     endif()
 endforeach()
 
+# The ignored-error slot is declared in the public header but must have one
+# library definition. Compare its address from two translation units, and
+# compile the consumer-facing test with all ordinary warnings enabled: a
+# header-local TLS definition would both duplicate storage and warn when unused.
+add_executable(test_err_ignore_multitu
+               tests/err_ignore_multitu.c
+               tests/err_ignore_multitu_helper.c)
+target_include_directories(test_err_ignore_multitu
+                           PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/tests)
+target_link_libraries(test_err_ignore_multitu PRIVATE akerror)
+target_compile_options(test_err_ignore_multitu PRIVATE -Wall -Wextra -Werror)
+if(AKERR_THREAD_SAFE)
+    target_link_libraries(test_err_ignore_multitu PRIVATE Threads::Threads)
+endif()
+add_test(NAME err_ignore_multitu COMMAND test_err_ignore_multitu)
+
 # HANDLE_GROUP deliberately enters the next case label. Keep that public macro
 # compiling with the warning enabled, so a future macro edit cannot restore the
 # warning for consumers which adopt -Wextra.

tests/err_ignore_multitu.c

@@ -0,0 +1,18 @@
+#include "akerror.h"
+#include "err_ignore_multitu.h"
+#include <stdio.h>
+
+int main(void)
+{
+    akerr_ErrorContext **main_address = &__akerr_last_ignored;
+    akerr_ErrorContext **helper_address = akerr_multitu_snapshot_address();
+
+    if ( main_address != helper_address ) {
+	fprintf(stderr,
+		"CHECK FAILED: ignored-error storage differs between translation units\n");
+	return 1;
+    }
+
+    fprintf(stderr, "err_ignore_multitu ok\n");
+    return 0;
+}

tests/err_ignore_multitu.h

@@ -0,0 +1,8 @@
+#ifndef AKERR_TEST_IGNORE_MULTITU_H
+#define AKERR_TEST_IGNORE_MULTITU_H
+
+#include "akerror.h"
+
+akerr_ErrorContext **akerr_multitu_snapshot_address(void);
+
+#endif

tests/err_ignore_multitu_helper.c

@@ -0,0 +1,6 @@
+#include "err_ignore_multitu.h"
+
+akerr_ErrorContext **akerr_multitu_snapshot_address(void)
+{
+    return &__akerr_last_ignored;
+}