bpo-36142: PYTHONMALLOC overrides PYTHONDEV (GH-12191)

bpo-34247, bpo-36142: The PYTHONMALLOC environment variable has the
priority over PYTHONDEV env var and "-X dev" command line option.
For example, PYTHONMALLOC=malloc PYTHONDEVMODE=1 sets the memory
allocators to "malloc" (and not to "debug").

Add an unit test.

1 files changed, 11 insertions, 7 deletions

diff --git a/Python/preconfig.c b/Python/preconfig.c
index 45093d2718..50d66b1249 100644
--- a/Python/preconfig.c
+++ b/Python/preconfig.c
@@ -445,14 +445,11 @@ preconfig_read(_PyPreConfig *config, const _PyPreCmdline *cmdline)
     }
 
     /* allocator */
-    if (config->dev_mode && config->allocator == NULL) {
-        config->allocator = _PyMem_RawStrdup("debug");
-        if (config->allocator == NULL) {
-            return _Py_INIT_NO_MEMORY();
-        }
-    }
-
     if (config->allocator == NULL) {
+        /* bpo-34247. The PYTHONMALLOC environment variable has the priority
+           over PYTHONDEV env var and "-X dev" command line option.
+           For example, PYTHONMALLOC=malloc PYTHONDEVMODE=1 sets the memory
+           allocators to "malloc" (and not to "debug"). */
         const char *allocator = _PyPreConfig_GetEnv(config, "PYTHONMALLOC");
         if (allocator) {
             config->allocator = _PyMem_RawStrdup(allocator);
@@ -462,6 +459,13 @@ preconfig_read(_PyPreConfig *config, const _PyPreCmdline *cmdline)
         }
     }
 
+    if (config->dev_mode && config->allocator == NULL) {
+        config->allocator = _PyMem_RawStrdup("debug");
+        if (config->allocator == NULL) {
+            return _Py_INIT_NO_MEMORY();
+        }
+    }
+
     assert(config->coerce_c_locale >= 0);
     assert(config->utf8_mode >= 0);
     assert(config->isolated >= 0);