gh-124697: avoid duplicate names in the same frame

Doc/library/dis.rst

@@ -2003,6 +2003,16 @@ but are replaced by real opcodes or removed before bytecode is generated.
    .. versionchanged:: 3.13
       This opcode is now a pseudo-instruction.
 
+.. opcode:: STORE_CLOSURE (i)
+
+   Stores the TOS into the cell slot ``i`` of the "fast locals" storage.
+   Used to restore a cell saved by ``LOAD_CLOSURE`` when isolating an
+   inlined comprehension that reuses an enclosing free variable.
+
+   Note that ``STORE_CLOSURE`` is replaced with ``STORE_FAST`` in the assembler.
+
+   .. versionadded:: next
+
 
 .. _opcode_collections:
 

Include/internal/pycore_interpframe.h

@@ -376,6 +376,12 @@ _PyFrame_Traverse(_PyInterpreterFrame *frame, visitproc visit, void *arg);
 bool
 _PyFrame_HasHiddenLocals(_PyInterpreterFrame *frame);
 
+/* True when localsplus[oparg] is a free cell that currently differs from
+ * the function's func_closure cell — i.e. an inlined comprehension has
+ * temporarily replaced it. */
+PyAPI_FUNC(bool)
+_PyFrame_IsInlinedCompTempFree(_PyInterpreterFrame *frame, int oparg);
+
 PyObject *
 _PyFrame_GetLocals(_PyInterpreterFrame *frame);
 

InternalDocs/inlined_comprehensions.md

@@ -86,15 +86,35 @@ The walk stops at a class: nested scopes do not see class locals.
 Class-closure names that would otherwise be free through a class become
 `GLOBAL_IMPLICIT`.
 
+If the inlined name is `LOCAL` or `CELL` but the nearest non-inlined
+enclosing table has it as `FREE` (or `DEF_FREE_CLASS`), resolve it as
+`FREE` so the comprehension reuses that localsplus slot.
+`compiler_cellvars()` also skips adding those child cells, which would
+otherwise create a second same-named entry. Class-closure names
+(`__class__` and friends) are never reused: zero-arg `super()` and
+class-cell bookkeeping need the real free cell.
+
 ### Isolating iteration variables
 
 `codegen_push_inlined_comprehension_locals()` in
-[`Python/codegen.c`](../Python/codegen.c) isolates names bound in the
-comprehension:
+[`Python/codegen.c`](../Python/codegen.c) isolates each name bound in
+the comprehension on one of two paths:
+
+Reuse an enclosing free (`_PyCompile_GetRefType()` is `FREE`):
+
+* `LOAD_CLOSURE` saves the enclosing cell without clearing the slot
+  (so free-slot introspection never sees a NULL).
+* `MAKE_CELL` on a `CO_FAST_FREE` slot always installs a fresh empty
+  cell, replacing the saved one. The comprehension then uses `DEREF`.
+* Restore uses `STORE_CLOSURE` (a cell/free-index pseudo that becomes
+  `STORE_FAST` after `fix_cell_offsets`).
 
-* `LOAD_FAST_AND_CLEAR` saves the enclosing value (possibly `NULL`) and
-  clears the slot.
-* `MAKE_CELL` runs if the name is a cell for this comprehension.
+Own fast-local slot (everything else):
+
+* `LOAD_FAST_AND_CLEAR` saves the enclosing value (possibly `NULL`)
+  and clears the slot.
+* `MAKE_CELL` runs only if the name is a cell for this comprehension.
+* Restore uses `STORE_FAST_MAYBE_NULL`.
 * In module and class units the name is added to `u_fasthidden` so
   assemble can set `CO_FAST_HIDDEN`.
 
@@ -105,10 +125,19 @@ or `finally` sees the original values.
 Runtime
 -------
 
-An inlined comprehension cell can share a localsplus name with an
-enclosing free variable (for example `[lambda: x for x in x]` inside a
-nested function). `FrameLocalsProxy` keys, values, items, and `len`
-keep the first slot of each name so they agree with `getitem`.
+An inlined comprehension local that collides with an enclosing free
+(for example `[x for x in x]` or `[lambda: x for x in x]` inside a
+nested function) reuses the free slot. Isolation saves that cell and
+installs a temporary one so `STORE_DEREF` does not change the value
+seen by existing closures; lambdas that capture the iteration variable
+share the temporary cell. After the comprehension, the original cell
+is restored.
+
+While the temporary cell is installed, `_PyFrame_IsInlinedCompTempFree()`
+is true (frame cell differs from `func_closure`). That drives
+class/module `locals()` to use `FrameLocalsProxy` even without a
+`CO_FAST_HIDDEN` slot, and makes an empty temporary cell raise
+`UnboundLocalError` rather than `NameError`.
 
 Source
 ------
@@ -128,5 +157,3 @@ Source
   `InlinedComprehensionBlock`
 * [`Include/internal/pycore_compile.h`](../Include/internal/pycore_compile.h):
   `_PyCompile_InlinedComprehensionState`
-* [`Objects/frameobject.c`](../Objects/frameobject.c):
-  `FrameLocalsProxy` duplicate-name handling