From bab2f102a1eb075e7fd9a55cc545b25a8efb35ae Mon Sep 17 00:00:00 2001
From: Logikoma <logikoma@aklabs.net>
Date: Wed, 5 Aug 2026 23:34:47 -0400
Subject: [PATCH] Test ignored-error storage across translation units

---
 CMakeLists.txt                    | 16 ++++++++++++++++
 include/akerror.tmpl.h            |  2 +-
 src/error.c                       |  1 +
 tests/err_ignore_multitu.c        | 18 ++++++++++++++++++
 tests/err_ignore_multitu.h        |  8 ++++++++
 tests/err_ignore_multitu_helper.c |  6 ++++++
 6 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 tests/err_ignore_multitu.c
 create mode 100644 tests/err_ignore_multitu.h
 create mode 100644 tests/err_ignore_multitu_helper.c

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0770138..b3b275a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -402,6 +402,22 @@ 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.
diff --git a/include/akerror.tmpl.h b/include/akerror.tmpl.h
index 851bb77..636ab2f 100644
--- a/include/akerror.tmpl.h
+++ b/include/akerror.tmpl.h
@@ -216,7 +216,7 @@ extern akerr_ErrorLogFunction akerr_log_method;
  * after the pool slot is reused. The snapshot is read-only and is replaced by
  * the next ignored error. Thread local only when AKERR_THREAD_SAFE is 1.
  */
-static AKERR_THREAD_LOCAL akerr_ErrorContext akerr_last_ignored;
+extern AKERR_THREAD_LOCAL akerr_ErrorContext akerr_last_ignored;
 
 /*
  * Drop one reference, returning NULL once the last one is gone so the caller can
diff --git a/src/error.c b/src/error.c
index 53a5a17..9b2971d 100644
--- a/src/error.c
+++ b/src/error.c
@@ -28,6 +28,7 @@
  * template header because the macro copies into it at the call site.
  */
 static AKERR_THREAD_LOCAL akerr_ErrorContext __akerr_last_ditch;
+AKERR_THREAD_LOCAL akerr_ErrorContext akerr_last_ignored;
 akerr_ErrorUnhandledErrorHandler akerr_handler_unhandled_error;
 akerr_ErrorLogFunction akerr_log_method = NULL;
 
diff --git a/tests/err_ignore_multitu.c b/tests/err_ignore_multitu.c
new file mode 100644
index 0000000..6d89d8e
--- /dev/null
+++ b/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;
+}
diff --git a/tests/err_ignore_multitu.h b/tests/err_ignore_multitu.h
new file mode 100644
index 0000000..17f2f9e
--- /dev/null
+++ b/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
diff --git a/tests/err_ignore_multitu_helper.c b/tests/err_ignore_multitu_helper.c
new file mode 100644
index 0000000..2994089
--- /dev/null
+++ b/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;
+}