[mypyc] Add librt.strings.isidentifier codepoint primitive

mypy/typeshed/stubs/librt/librt/strings.pyi

@@ -47,3 +47,4 @@ def isspace(c: i32, /) -> bool: ...
 def isdigit(c: i32, /) -> bool: ...
 def isalnum(c: i32, /) -> bool: ...
 def isalpha(c: i32, /) -> bool: ...
+def isidentifier(c: i32, /) -> bool: ...

mypyc/lib-rt/codepoint_extra_ops.c

@@ -1,8 +1,6 @@
+// All codepoint helper bodies live in codepoint_extra_ops.h as static
+// inline. This translation unit exists so the header is pulled into
+// mypyc-compiled extensions via SourceDep("codepoint_extra_ops.c") in
+// mypyc/ir/deps.py (which, in include_runtime_files mode, emits
+// `#include <codepoint_extra_ops.c>` into the generated __native.c).
 #include "codepoint_extra_ops.h"
-
-// Out-of-line bodies for codepoint helpers that are too large to inline.
-// The classification helpers and the ASCII fast paths for case conversion
-// stay inline in codepoint_extra_ops.h; this file holds the slow paths
-// that round-trip through PyUnicode_FromOrdinal and CPython's Unicode
-// machinery. Currently empty; populated as later commits add
-// isidentifier, toupper, and tolower.

mypyc/lib-rt/codepoint_extra_ops.h

@@ -4,6 +4,7 @@
 #include <Python.h>
 #include <stdbool.h>
 #include <stdint.h>
+#include "CPy.h"
 
 // Codepoint helpers for librt.strings.
 // Inputs are signed int32_t for compatibility with mypyc's i32 type.
@@ -25,4 +26,26 @@ static inline bool LibRTStrings_IsAlpha(int32_t c) {
     return c >= 0 && Py_UNICODE_ISALPHA((Py_UCS4)c);
 }
 
+// True if c could start a valid identifier (matches XID_Start
+// semantics, which is what str.isidentifier reports for a 1-character
+// string). The ASCII fast path covers `[A-Za-z_]` inline; non-ASCII
+// delegates to PyUnicode_IsIdentifier for correct PEP 3131 handling.
+// Aborts via CPyError_OutOfMemory on allocation failure, so this helper
+// stays ERR_NEVER.
+static inline bool LibRTStrings_IsIdentifier(int32_t c) {
+    if (c < 0) return false;
+    if (c < 128) {
+        return (c >= 'a' && c <= 'z')
+            || (c >= 'A' && c <= 'Z')
+            || c == '_';
+    }
+    PyObject *s = PyUnicode_FromOrdinal((int)c);
+    if (s == NULL) {
+        CPyError_OutOfMemory();
+    }
+    int r = PyUnicode_IsIdentifier(s);
+    Py_DECREF(s);
+    return r == 1;
+}
+
 #endif  // MYPYC_CODEPOINT_EXTRA_OPS_H

mypyc/lib-rt/strings/librt_strings.c

@@ -1194,6 +1194,7 @@ DEFINE_CP_BOOL_WRAPPER(isspace, LibRTStrings_IsSpace)
 DEFINE_CP_BOOL_WRAPPER(isdigit, LibRTStrings_IsDigit)
 DEFINE_CP_BOOL_WRAPPER(isalnum, LibRTStrings_IsAlnum)
 DEFINE_CP_BOOL_WRAPPER(isalpha, LibRTStrings_IsAlpha)
+DEFINE_CP_BOOL_WRAPPER(isidentifier, LibRTStrings_IsIdentifier)
 
 static PyMethodDef librt_strings_module_methods[] = {
     {"write_i16_le", (PyCFunction) write_i16_le, METH_FASTCALL,
@@ -1268,6 +1269,9 @@ static PyMethodDef librt_strings_module_methods[] = {
     {"isalpha", cp_isalpha, METH_O,
      PyDoc_STR("Test whether a codepoint (i32) is a Unicode letter.")
     },
+    {"isidentifier", cp_isidentifier, METH_O,
+     PyDoc_STR("Test whether a codepoint (i32) is a valid identifier start (XID_Start).")
+    },
     {NULL, NULL, 0, NULL}
 };
 

mypyc/primitives/librt_strings_ops.py

@@ -431,3 +431,15 @@
     error_kind=ERR_NEVER,
     dependencies=[LIBRT_STRINGS, CODEPOINT_EXTRA_OPS],
 )
+
+# isidentifier checks XID_Start semantics for a single codepoint, matching
+# str.isidentifier() on a 1-character string. The non-ASCII path allocates
+# but swallows OOM (returning False), keeping the function ERR_NEVER.
+function_op(
+    name="librt.strings.isidentifier",
+    arg_types=[int32_rprimitive],
+    return_type=bool_rprimitive,
+    c_function_name="LibRTStrings_IsIdentifier",
+    error_kind=ERR_NEVER,
+    dependencies=[LIBRT_STRINGS, CODEPOINT_EXTRA_OPS],
+)

mypyc/test-data/irbuild-librt-strings.test

@@ -387,3 +387,17 @@ def is_a(c):
 L0:
     r0 = LibRTStrings_IsAlpha(c)
     return r0
+
+[case testLibrtStringsIsIdentifierIR]
+from librt.strings import isidentifier
+from mypy_extensions import i32
+
+def is_id(c: i32) -> bool:
+    return isidentifier(c)
+[out]
+def is_id(c):
+    c :: i32
+    r0 :: bool
+L0:
+    r0 = LibRTStrings_IsIdentifier(c)
+    return r0

mypyc/test-data/run-librt-strings.test

@@ -1443,7 +1443,7 @@ def test_new_without_init_is_usable() -> None:
 [case testLibrtStringsCodepointClassifiers_librt]
 from typing import Any
 from mypy_extensions import i32
-from librt.strings import isspace, isdigit, isalnum, isalpha
+from librt.strings import isspace, isdigit, isalnum, isalpha, isidentifier
 
 from testutil import assertRaises
 
@@ -1455,6 +1455,7 @@ def test_codepoint_classifiers() -> None:
         assert not isdigit(bad)
         assert not isalnum(bad)
         assert not isalpha(bad)
+        assert not isidentifier(bad)
     # Verify each codepoint primitive agrees with the matching str method
     # across all Unicode codepoints, including the ord(chr(i)) round-trip.
     # Any forces generic dispatch on the str side.
@@ -1466,6 +1467,7 @@ def test_codepoint_classifiers() -> None:
         assert isdigit(o) == isdigit(i) == a.isdigit()
         assert isalnum(o) == isalnum(i) == a.isalnum()
         assert isalpha(o) == isalpha(i) == a.isalpha()
+        assert isidentifier(o) == isidentifier(i) == a.isidentifier()
 
 
 def test_codepoint_classifiers_via_any() -> None:
@@ -1476,6 +1478,7 @@ def test_codepoint_classifiers_via_any() -> None:
         (isdigit, "5", "a"),
         (isalnum, "A", " "),
         (isalpha, "A", " "),
+        (isidentifier, "A", "0"),
     ):
         f: Any = fn
         assert f(ord(true_input)) is True