[clang] [BoundsSafety][Sema] Allow counted_by and counted_by_or_null on pointers where the pointee type is incomplete but potentially completable (PR #106321)

[via cfe-commits]

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+// RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fexperimental-late-parse-attributes -fsyntax-only -verify %s
+
+#define __counted_by(f)  __attribute__((counted_by(f)))
+
+// =============================================================================
+// # Struct incomplete type with attribute in the decl position
+// =============================================================================
+
+// Note: This could be considered misleading. The typedef isn't actually on this
+// line. Also note the discrepancy in diagnostic count (27 vs 51) is due to
+// the pointer arithmetic on incomplete pointee type diagnostic always using
+// diagnostic text that refers to the underlying forward decl, even when the
+// typedef is used.
+// expected-note at +1 27{{forward declaration of 'Incomplete_t' (aka 'struct IncompleteTy')}}
+struct IncompleteTy; // expected-note 51{{forward declaration of 'struct IncompleteTy'}}
+
+typedef struct IncompleteTy Incomplete_t; 
+
+struct CBBufDeclPos {
+  int count;
+  struct IncompleteTy* buf __counted_by(count); // OK expected-note 27{{__counted_by attribute is here}}
+  Incomplete_t* buf_typedef __counted_by(count); // OK expected-note 27{{__counted_by attribute is here}}
+};
+
+void consume_struct_IncompleteTy(struct IncompleteTy* buf);
+
+int idx(void);
+
+
+
+void test_CBBufDeclPos(struct CBBufDeclPos* ptr) {
+  // ===========================================================================
+  // ## Local variable initialization
+  // ===========================================================================
+  struct CBBufDeclPos explicit_desig_init = {
+    .count = 0,
+    // expected-error at +1{{cannot initialize 'CBBufDeclPos::buf' that has type 'struct IncompleteTy * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'struct IncompleteTy' is incomplete and the '__counted_by' attribute requires the pointee type be complete when initializing; consider providing a complete definition for 'struct IncompleteTy' or using the '__sized_by' attribute}}
+    .buf = 0x0,
+    // expected-error at +1{{cannot initialize 'CBBufDeclPos::buf_typedef' that has type 'Incomplete_t * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'Incomplete_t' (aka 'struct IncompleteTy') is incomplete and the '__counted_by' attribute requires the pointee type be complete when initializing; consider providing a complete definition for 'Incomplete_t' or using the '__sized_by' attribute}}
+    .buf_typedef = 0x0
+  };
+  // Variable is not currently marked as invalid so uses of the variable allows
+  // diagnostics to fire.
+  // expected-error at +1{{cannot assign to 'CBBufDeclPos::buf' that has type 'struct IncompleteTy * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'struct IncompleteTy' is incomplete and the '__counted_by' attribute requires the pointee type be complete when assigning; consider providing a complete definition for 'struct IncompleteTy' or using the '__sized_by' attribute}}
+  explicit_desig_init.buf = 0x0;
+  // expected-error at +1{{cannot assign to 'CBBufDeclPos::buf_typedef' that has type 'Incomplete_t * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'Incomplete_t' (aka 'struct IncompleteTy') is incomplete and the '__counted_by' attribute requires the pointee type be complete when assigning; consider providing a complete definition for 'Incomplete_t' or using the '__sized_by' attribute}}
+  explicit_desig_init.buf_typedef = 0x0;
+  // expected-error at +1{{cannot use 'explicit_desig_init.buf' with type 'struct IncompleteTy * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'struct IncompleteTy' is incomplete and the '__counted_by' attribute requires the pointee type be complete in this context; consider providing a complete definition for 'struct IncompleteTy' or using the '__sized_by' attribute}}
+  void *tmp = explicit_desig_init.buf;
+  // expected-error at +1{{cannot use 'explicit_desig_init.buf_typedef' with type 'Incomplete_t * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'Incomplete_t' (aka 'struct IncompleteTy') is incomplete and the '__counted_by' attribute requires the pointee type be complete in this context; consider providing a complete definition for 'Incomplete_t' or using the '__sized_by' attribute}}
+  void *tmp2 = explicit_desig_init.buf_typedef;
+
+  struct CBBufDeclPos partial_explicit_desig_init = {
+    .count = 0,
+    // .buf and .buf_typedef are implicit zero initialized
+    // expected-error at +2{{cannot implicitly initialize 'CBBufDeclPos::buf' that has type 'struct IncompleteTy * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'struct IncompleteTy' is incomplete and the '__counted_by' attribute requires the pointee type be complete when initializing; consider providing a complete definition for 'struct IncompleteTy' or using the '__sized_by' attribute}}
+    // expected-error at +1{{cannot implicitly initialize 'CBBufDeclPos::buf_typedef' that has type 'Incomplete_t * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'Incomplete_t' (aka 'struct IncompleteTy') is incomplete and the '__counted_by' attribute requires the pointee type be complete when initializing; consider providing a complete definition for 'Incomplete_t' or using the '__sized_by' attribute}}
+  };
+
+  struct CBBufDeclPos implicit_full_init = {
+    0
+    // expected-error at +2{{cannot implicitly initialize 'CBBufDeclPos::buf' that has type 'struct IncompleteTy * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'struct IncompleteTy' is incomplete and the '__counted_by' attribute requires the pointee type be complete when initializing; consider providing a complete definition for 'struct IncompleteTy' or using the '__sized_by' attribute}}
+    // expected-error at +1{{cannot implicitly initialize 'CBBufDeclPos::buf_typedef' that has type 'Incomplete_t * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'Incomplete_t' (aka 'struct IncompleteTy') is incomplete and the '__counted_by' attribute requires the pointee type be complete when initializing; consider providing a complete definition for 'Incomplete_t' or using the '__sized_by' attribute}}
+  };
+  // Variable is not currently marked as invalid so uses of the variable allows
+  // diagnostics to fire.
+  // expected-error at +1{{cannot assign to 'CBBufDeclPos::buf' that has type 'struct IncompleteTy * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'struct IncompleteTy' is incomplete and the '__counted_by' attribute requires the pointee type be complete when assigning; consider providing a complete definition for 'struct IncompleteTy' or using the '__sized_by' attribute}}
+  implicit_full_init.buf = 0x0;
+  // expected-error at +1{{cannot assign to 'CBBufDeclPos::buf_typedef' that has type 'Incomplete_t * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'Incomplete_t' (aka 'struct IncompleteTy') is incomplete and the '__counted_by' attribute requires the pointee type be complete when assigning; consider providing a complete definition for 'Incomplete_t' or using the '__sized_by' attribute}}
+  implicit_full_init.buf_typedef = 0x0;
+  // expected-error at +1{{cannot use 'implicit_full_init.buf' with type 'struct IncompleteTy * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'struct IncompleteTy' is incomplete and the '__counted_by' attribute requires the pointee type be complete in this context; consider providing a complete definition for 'struct IncompleteTy' or using the '__sized_by' attribute}}
+  void* tmp3 = implicit_full_init.buf;
+  // expected-error at +1{{cannot use 'implicit_full_init.buf_typedef' with type 'Incomplete_t * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'Incomplete_t' (aka 'struct IncompleteTy') is incomplete and the '__counted_by' attribute requires the pointee type be complete in this context; consider providing a complete definition for 'Incomplete_t' or using the '__sized_by' attribute}}
+  void* tmp4 = implicit_full_init.buf_typedef;
+  
+  struct CBBufDeclPos explicit_non_desig_init = {
+    0,
+    // expected-error at +1{{cannot initialize 'CBBufDeclPos::buf' that has type 'struct IncompleteTy * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'struct IncompleteTy' is incomplete and the '__counted_by' attribute requires the pointee type be complete when initializing; consider providing a complete definition for 'struct IncompleteTy' or using the '__sized_by' attribute}}
+    0x0,
+    // expected-error at +1{{cannot initialize 'CBBufDeclPos::buf_typedef' that has type 'Incomplete_t * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'Incomplete_t' (aka 'struct IncompleteTy') is incomplete and the '__counted_by' attribute requires the pointee type be complete when initializing; consider providing a complete definition for 'Incomplete_t' or using the '__sized_by' attribute}}
+    0x0
+  };
+
+  // ===========================================================================
+  // ## Assignment to fields
+  // ===========================================================================
+  struct CBBufDeclPos uninit;
+  uninit.count = 0;
+  // expected-error at +1{{cannot assign to 'CBBufDeclPos::buf' that has type 'struct IncompleteTy * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'struct IncompleteTy' is incomplete and the '__counted_by' attribute requires the pointee type be complete when assigning; consider providing a complete definition for 'struct IncompleteTy' or using the '__sized_by' attribute}}
+  uninit.buf = 0x0;
+  // expected-error at +1{{cannot assign to 'CBBufDeclPos::buf_typedef' that has type 'Incomplete_t * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'Incomplete_t' (aka 'struct IncompleteTy') is incomplete and the '__counted_by' attribute requires the pointee type be complete when assigning; consider providing a complete definition for 'Incomplete_t' or using the '__sized_by' attribute}}
+  uninit.buf_typedef = 0x0;
+  ptr->count = 0;
+  // expected-error at +1{{cannot assign to 'CBBufDeclPos::buf' that has type 'struct IncompleteTy * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'struct IncompleteTy' is incomplete and the '__counted_by' attribute requires the pointee type be complete when assigning; consider providing a complete definition for 'struct IncompleteTy' or using the '__sized_by' attribute}}
+  ptr->buf = 0x0;
+  // expected-error at +1{{cannot assign to 'CBBufDeclPos::buf_typedef' that has type 'Incomplete_t * __counted_by(count)' (aka 'struct IncompleteTy *') because the pointee type 'Incomplete_t' (aka 'struct IncompleteTy') is incomplete and the '__counted_by' attribute requires the pointee type be complete when assigning; consider providing a complete definition for 'Incomplete_t' or using the '__sized_by' attribute}}
+  ptr->buf_typedef = 0x0;
+
+
+  // ===========================================================================
+  // ## Make sure modifying the fields through other assignment operators is not
+  //    allowed
+  // ===========================================================================
----------------
Sirraide wrote:

> Yes... but it's specifically testing we are disallowing pointer arithmetic on pointers with the `__counted_by` attribute which is unlikely to be tested elsewhere.

It’s fine to have tests for that sure, but my point is that if you try to perform pointer arithmetic on an *incomplete* type, we’re going to reject that anyway, irrespective of whether the member in question has the `__counted_by` attribute or not (https://godbolt.org/z/Ws8d38z6K).

So if you want to add test for arithmetic on `__counted_by`-attributed types, the type should be complete for that.

https://github.com/llvm/llvm-project/pull/106321