gh-76785: Add PyInterpreterConfig Helpers (gh-117170)

These helpers make it easier to customize and inspect the config used to initialize interpreters.  This is especially valuable in our tests.  I found inspiration from the PyConfig API for the PyInterpreterConfig dict conversion stuff.  As part of this PR I've also added a bunch of tests.

3 files changed, 305 insertions, 22 deletions

diff --git a/Python/config_common.h b/Python/config_common.h
new file mode 100644
index 0000000..e749bd4
--- /dev/null
+++ b/Python/config_common.h
@@ -0,0 +1,36 @@
+
+static inline int
+_config_dict_get(PyObject *dict, const char *name, PyObject **p_item)
+{
+    PyObject *item;
+    if (PyDict_GetItemStringRef(dict, name, &item) < 0) {
+        return -1;
+    }
+    if (item == NULL) {
+        // We do not set an exception.
+        return -1;
+    }
+    *p_item = item;
+    return 0;
+}
+
+
+static PyObject*
+config_dict_get(PyObject *dict, const char *name)
+{
+    PyObject *item;
+    if (_config_dict_get(dict, name, &item) < 0) {
+        if (!PyErr_Occurred()) {
+            PyErr_Format(PyExc_ValueError, "missing config key: %s", name);
+        }
+        return NULL;
+    }
+    return item;
+}
+
+
+static void
+config_dict_invalid_type(const char *name)
+{
+    PyErr_Format(PyExc_TypeError, "invalid config type: %s", name);
+}
diff --git a/Python/initconfig.c b/Python/initconfig.c
index 215d6a1..d91a819 100644
--- a/Python/initconfig.c
+++ b/Python/initconfig.c
@@ -24,6 +24,9 @@
 #  endif
 #endif
 
+#include "config_common.h"
+
+
 /* --- PyConfig spec ---------------------------------------------- */
 
 typedef enum {
@@ -1098,21 +1101,6 @@ _PyConfig_AsDict(const PyConfig *config)
 }
 
 
-static PyObject*
-config_dict_get(PyObject *dict, const char *name)
-{
-    PyObject *item;
-    if (PyDict_GetItemStringRef(dict, name, &item) < 0) {
-        return NULL;
-    }
-    if (item == NULL) {
-        PyErr_Format(PyExc_ValueError, "missing config key: %s", name);
-        return NULL;
-    }
-    return item;
-}
-
-
 static void
 config_dict_invalid_value(const char *name)
 {
@@ -1120,13 +1108,6 @@ config_dict_invalid_value(const char *name)
 }
 
 
-static void
-config_dict_invalid_type(const char *name)
-{
-    PyErr_Format(PyExc_TypeError, "invalid config type: %s", name);
-}
-
-
 static int
 config_dict_get_int(PyObject *dict, const char *name, int *result)
 {
diff --git a/Python/interpconfig.c b/Python/interpconfig.c
new file mode 100644
index 0000000..419f40a
--- /dev/null
+++ b/Python/interpconfig.c
@@ -0,0 +1,266 @@
+/* PyInterpreterConfig API */
+
+#include "Python.h"
+#include "pycore_pylifecycle.h"
+
+#include <stdbool.h>
+
+#include "config_common.h"
+
+
+static const char *
+gil_flag_to_str(int flag)
+{
+    switch (flag) {
+    case PyInterpreterConfig_DEFAULT_GIL:
+        return "default";
+    case PyInterpreterConfig_SHARED_GIL:
+        return "shared";
+    case PyInterpreterConfig_OWN_GIL:
+        return "own";
+    default:
+        PyErr_SetString(PyExc_SystemError,
+                        "invalid interpreter config 'gil' value");
+        return NULL;
+    }
+}
+
+static int
+gil_flag_from_str(const char *str, int *p_flag)
+{
+    int flag;
+    if (str == NULL) {
+        flag = PyInterpreterConfig_DEFAULT_GIL;
+    }
+    else if (strcmp(str, "default") == 0) {
+        flag = PyInterpreterConfig_DEFAULT_GIL;
+    }
+    else if (strcmp(str, "shared") == 0) {
+        flag = PyInterpreterConfig_SHARED_GIL;
+    }
+    else if (strcmp(str, "own") == 0) {
+        flag = PyInterpreterConfig_OWN_GIL;
+    }
+    else {
+        PyErr_Format(PyExc_ValueError,
+                     "unsupported interpreter config .gil value '%s'", str);
+        return -1;
+    }
+    *p_flag = flag;
+    return 0;
+}
+
+PyObject *
+_PyInterpreterConfig_AsDict(PyInterpreterConfig *config)
+{
+    PyObject *dict = PyDict_New();
+    if (dict == NULL) {
+        return NULL;
+    }
+
+#define ADD(NAME, OBJ)                                              \
+        do {                                                        \
+            int res = PyDict_SetItemString(dict, NAME, (OBJ));      \
+            Py_DECREF(OBJ);                                         \
+            if (res < 0) {                                          \
+                goto error;                                         \
+            }                                                       \
+        } while (0)
+#define ADD_BOOL(FIELD) \
+        ADD(#FIELD, Py_NewRef(config->FIELD ? Py_True : Py_False))
+#define ADD_STR(FIELD, STR)                                         \
+        do {                                                        \
+            if (STR == NULL) {                                      \
+                goto error;                                         \
+            }                                                       \
+            PyObject *obj = PyUnicode_FromString(STR);              \
+            if (obj == NULL) {                                      \
+                goto error;                                         \
+            }                                                       \
+            ADD(#FIELD, obj);                                       \
+        } while (0)
+
+    ADD_BOOL(use_main_obmalloc);
+    ADD_BOOL(allow_fork);
+    ADD_BOOL(allow_exec);
+    ADD_BOOL(allow_threads);
+    ADD_BOOL(allow_daemon_threads);
+    ADD_BOOL(check_multi_interp_extensions);
+
+    ADD_STR(gil, gil_flag_to_str(config->gil));
+
+#undef ADD_STR
+#undef ADD_BOOL
+#undef ADD
+
+    return dict;
+
+error:
+    Py_DECREF(dict);
+    return NULL;
+}
+
+static int
+_config_dict_get_bool(PyObject *dict, const char *name, int *p_flag)
+{
+    PyObject *item;
+    if (_config_dict_get(dict, name, &item) < 0) {
+        return -1;
+    }
+    // For now we keep things strict, rather than using PyObject_IsTrue().
+    int flag = item == Py_True;
+    if (!flag && item != Py_False) {
+        Py_DECREF(item);
+        config_dict_invalid_type(name);
+        return -1;
+    }
+    Py_DECREF(item);
+    *p_flag = flag;
+    return 0;
+}
+
+static int
+_config_dict_copy_str(PyObject *dict, const char *name,
+                      char *buf, size_t bufsize)
+{
+    PyObject *item;
+    if (_config_dict_get(dict, name, &item) < 0) {
+        return -1;
+    }
+    if (!PyUnicode_Check(item)) {
+        Py_DECREF(item);
+        config_dict_invalid_type(name);
+        return -1;
+    }
+    strncpy(buf, PyUnicode_AsUTF8(item), bufsize-1);
+    buf[bufsize-1] = '\0';
+    Py_DECREF(item);
+    return 0;
+}
+
+static int
+interp_config_from_dict(PyObject *origdict, PyInterpreterConfig *config,
+                        bool missing_allowed)
+{
+    PyObject *dict = PyDict_New();
+    if (dict == NULL) {
+        return -1;
+    }
+    if (PyDict_Update(dict, origdict) < 0) {
+        goto error;
+    }
+
+#define CHECK(NAME)                                                 \
+    do {                                                            \
+        if (PyErr_Occurred()) {                                     \
+            goto error;                                             \
+        }                                                           \
+        else {                                                      \
+            if (!missing_allowed) {                                 \
+                (void)config_dict_get(dict, NAME);                  \
+                assert(PyErr_Occurred());                           \
+                goto error;                                         \
+            }                                                       \
+        }                                                           \
+    } while (0)
+#define COPY_BOOL(FIELD)                                            \
+    do {                                                            \
+        int flag;                                                   \
+        if (_config_dict_get_bool(dict, #FIELD, &flag) < 0) {       \
+            CHECK(#FIELD);                                          \
+        }                                                           \
+        else {                                                      \
+            config->FIELD = flag;                                   \
+            (void)PyDict_PopString(dict, #FIELD, NULL);             \
+        }                                                           \
+    } while (0)
+
+    COPY_BOOL(use_main_obmalloc);
+    COPY_BOOL(allow_fork);
+    COPY_BOOL(allow_exec);
+    COPY_BOOL(allow_threads);
+    COPY_BOOL(allow_daemon_threads);
+    COPY_BOOL(check_multi_interp_extensions);
+
+    // PyInterpreterConfig.gil
+    char buf[20];
+    if (_config_dict_copy_str(dict, "gil", buf, 20) < 0) {
+        CHECK("gil");
+    }
+    else {
+        int flag;
+        if (gil_flag_from_str(buf, &flag) < 0) {
+            goto error;
+        }
+        config->gil = flag;
+        (void)PyDict_PopString(dict, "gil", NULL);
+    }
+
+#undef COPY_BOOL
+#undef CHECK
+
+    Py_ssize_t unused = PyDict_GET_SIZE(dict);
+    if (unused == 1) {
+        PyErr_Format(PyExc_ValueError,
+                     "config dict has 1 extra item (%R)", dict);
+        goto error;
+    }
+    else if (unused > 0) {
+        PyErr_Format(PyExc_ValueError,
+                     "config dict has %d extra items (%R)", unused, dict);
+        goto error;
+    }
+    return 0;
+
+error:
+    Py_DECREF(dict);
+    return -1;
+}
+
+int
+_PyInterpreterConfig_InitFromDict(PyInterpreterConfig *config, PyObject *dict)
+{
+    if (!PyDict_Check(dict)) {
+        PyErr_SetString(PyExc_TypeError, "dict expected");
+        return -1;
+    }
+    if (interp_config_from_dict(dict, config, false) < 0) {
+        return -1;
+    }
+    return 0;
+}
+
+int
+_PyInterpreterConfig_UpdateFromDict(PyInterpreterConfig *config, PyObject *dict)
+{
+    if (!PyDict_Check(dict)) {
+        PyErr_SetString(PyExc_TypeError, "dict expected");
+        return -1;
+    }
+    if (interp_config_from_dict(dict, config, true) < 0) {
+        return -1;
+    }
+    return 0;
+}
+
+int
+_PyInterpreterConfig_InitFromState(PyInterpreterConfig *config,
+                                   PyInterpreterState *interp)
+{
+    // Populate the config by re-constructing the values from the interpreter.
+    *config = (PyInterpreterConfig){
+#define FLAG(flag) \
+        (interp->feature_flags & Py_RTFLAGS_ ## flag)
+        .use_main_obmalloc = FLAG(USE_MAIN_OBMALLOC),
+        .allow_fork = FLAG(FORK),
+        .allow_exec = FLAG(EXEC),
+        .allow_threads = FLAG(THREADS),
+        .allow_daemon_threads = FLAG(DAEMON_THREADS),
+        .check_multi_interp_extensions = FLAG(MULTI_INTERP_EXTENSIONS),
+#undef FLAG
+        .gil = interp->ceval.own_gil
+            ? PyInterpreterConfig_OWN_GIL
+            : PyInterpreterConfig_SHARED_GIL,
+    };
+    return 0;
+}