[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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@@ -0,0 +1,584 @@
+// 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}}
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Sirraide wrote:

> This is more succinct but it looses the important piece of information that is restriction comes from the `__counted_by` attribute which is really not obvious.

Maybe instead of `cannot use X with type ...`, we could write `cannot use X with '__counted_by'-attributed type ...`? I feel like that might be as short as we’ll be able to make it.

Also, in addition to that, maybe we can move the ‘consider completing the definition or using the '__sized_by' attribute instead’ to a note that points to the attribute location... if we have access to that here, that is (iirc there were some problems w/ that, but I’m not sure anymore)?

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