assert-util: introduce log_set_assert_return_is_critical_from_env()

It will be used for testing nss modules.

docs/ENVIRONMENT.md

@@ -454,6 +454,9 @@ systemd tests:
   causes all non-matching test functions to be skipped. Only applies to tests
   using our regular test boilerplate.
 
+* `$SYSTEMD_ASSERT_RETURN_IS_CRITICAL` — Takes a boolean to control if
+  `assert_return()` and friends call `abort()`.
+
 fuzzers:
 
 * `$SYSTEMD_FUZZ_OUTPUT` — A boolean that specifies whether to write output to

src/basic/assert-util.c

@@ -4,6 +4,7 @@
 #include <stdlib.h>
 
 #include "assert-util.h"
+#include "env-util.h"
 #include "errno-util.h"
 #include "log.h"
 
@@ -17,6 +18,22 @@ void log_set_assert_return_is_critical(bool b) {
         assert_return_is_critical = b;
 }
 
+void log_set_assert_return_is_critical_from_env(void) {
+        static int cached = INT_MIN;
+        int r;
+
+        if (cached == INT_MIN) {
+                r = secure_getenv_bool("SYSTEMD_ASSERT_RETURN_IS_CRITICAL");
+                if (r < 0 && r != -ENXIO)
+                        log_debug_errno(r, "Failed to parse $SYSTEMD_ASSERT_RETURN_IS_CRITICAL, ignoring: %m");
+
+                cached = r;
+        }
+
+        if (cached >= 0)
+                log_set_assert_return_is_critical(cached);
+}
+
 bool log_get_assert_return_is_critical(void) {
         return assert_return_is_critical;
 }

src/basic/assert-util.h

@@ -6,6 +6,7 @@
 /* Logging for various assertions */
 
 void log_set_assert_return_is_critical(bool b);
+void log_set_assert_return_is_critical_from_env(void);
 bool log_get_assert_return_is_critical(void) _pure_;
 
 void log_assert_failed_return(const char *text, const char *file, int line, const char *func);