Improve diagnostic wording for invalid callback attribute uses (#134423)

We were previously telling the user how many arguments were passed to
the attribute rather than saying how many arguments were expected to be
passed to the callback function. This rewords the diagnostic to
hopefully be a bit more clear.

Fixes #47451

Author: AaronBallman

clang/docs/ReleaseNotes.rst

@@ -367,6 +367,10 @@ Bug Fixes to Attribute Support
   or ``__attribute__((malloc(deallocator, ptr-index)))``
   (`#51607 <https://github.com/llvm/llvm-project/issues/51607>`_).
 
+- Corrected the diagnostic for the ``callback`` attribute when passing too many
+  or too few attribute argument indicies for the specified callback function.
+  (#GH47451)
+
 Bug Fixes to C++ Support
 ^^^^^^^^^^^^^^^^^^^^^^^^
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -3195,6 +3195,10 @@ def err_attribute_wrong_number_arguments : Error<
 def err_attribute_wrong_number_arguments_for : Error <
   "%0 attribute references function %1, which %plural{0:takes no arguments|1:takes one argument|"
   ":takes exactly %2 arguments}2">;
+def err_callback_attribute_wrong_arg_count : Error<
+  "'callback' attribute references function of type %0 which expects %1 "
+  "%plural{1:argument|:arguments}1 but attribute specifies %2 parameter index "
+  "%plural{1:argument|:arguments}2">;
 def err_attribute_bounds_for_function : Error<
   "%0 attribute references parameter %1, but the function %2 has only %3 parameters">;
 def err_attribute_no_member_function : Error<

clang/lib/Sema/SemaDeclAttr.cpp

@@ -4145,15 +4145,10 @@ static void handleCallbackAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
     return;
   }
 
-  if (CalleeFnProtoType->getNumParams() > EncodingIndices.size() - 1) {
-    S.Diag(AL.getLoc(), diag::err_attribute_wrong_number_arguments)
-        << AL << (unsigned)(EncodingIndices.size() - 1);
-    return;
-  }
-
-  if (CalleeFnProtoType->getNumParams() < EncodingIndices.size() - 1) {
-    S.Diag(AL.getLoc(), diag::err_attribute_wrong_number_arguments)
-        << AL << (unsigned)(EncodingIndices.size() - 1);
+  if (CalleeFnProtoType->getNumParams() != EncodingIndices.size() - 1) {
+    S.Diag(AL.getLoc(), diag::err_callback_attribute_wrong_arg_count)
+        << QualType{CalleeFnProtoType, 0} << CalleeFnProtoType->getNumParams()
+        << (unsigned)(EncodingIndices.size() - 1);
     return;
   }
 

clang/test/Sema/attr-callback-broken.c

@@ -2,13 +2,13 @@
 
 __attribute__((callback())) void no_callee(void (*callback)(void)); // expected-error {{'callback' attribute specifies no callback callee}}
 
-__attribute__((callback(1, 1))) void too_many_args_1(void (*callback)(void)) {}      // expected-error {{'callback' attribute takes one argument}}
-__attribute__((callback(1, -1))) void too_many_args_2(double (*callback)(void));     // expected-error {{'callback' attribute takes one argument}}
-__attribute__((callback(1, 2, 2))) void too_many_args_3(void (*callback)(int), int); // expected-error {{'callback' attribute requires exactly 2 arguments}}
+__attribute__((callback(1, 1))) void too_many_args_1(void (*callback)(void)) {}      // expected-error-re {{'callback' attribute references function of type 'void ({{(void)?}})' which expects 0 arguments but attribute specifies 1 parameter index argument}}
+__attribute__((callback(1, -1))) void too_many_args_2(double (*callback)(void));     // expected-error-re {{'callback' attribute references function of type 'double ({{(void)?}})' which expects 0 arguments but attribute specifies 1 parameter index argument}}
+__attribute__((callback(1, 2, 2))) void too_many_args_3(void (*callback)(int), int); // expected-error {{'callback' attribute references function of type 'void (int)' which expects 1 argument but attribute specifies 2 parameter index arguments}}
 
-__attribute__((callback(1, 2))) void too_few_args_1(void (*callback)(int, int), int); // expected-error {{'callback' attribute takes one argument}}
-__attribute__((callback(1))) void too_few_args_2(int (*callback)(int));               // expected-error {{'callback' attribute takes no arguments}}
-__attribute__((callback(1, -1))) void too_few_args_3(void (*callback)(int, int)) {}   // expected-error {{'callback' attribute takes one argument}}
+__attribute__((callback(1, 2))) void too_few_args_1(void (*callback)(int, int), int); // expected-error {{'callback' attribute references function of type 'void (int, int)' which expects 2 arguments but attribute specifies 1 parameter index argument}}
+__attribute__((callback(1))) void too_few_args_2(int (*callback)(int));               // expected-error {{'callback' attribute references function of type 'int (int)' which expects 1 argument but attribute specifies 0 parameter index arguments}}
+__attribute__((callback(1, -1))) void too_few_args_3(void (*callback)(int, int)) {}   // expected-error {{'callback' attribute references function of type 'void (int, int)' which expects 2 arguments but attribute specifies 1 parameter index argument}}
 
 __attribute__((callback(-1))) void oob_args_1(void (*callback)(void));         // expected-error {{'callback' attribute specifies invalid callback callee}}
 __attribute__((callback(2))) void oob_args_2(int *(*callback)(void)) {}        // expected-error {{'callback' attribute parameter 1 is out of bounds}}
@@ -33,22 +33,22 @@ __attribute__((callback(1, 0))) void no_this_2(void *(*callback)(int, void *));
 __attribute__((callback(1, -1))) void vararg_cb_1(void (*callback)(int, ...)) {}     // expected-error {{'callback' attribute callee may not be variadic}}
 __attribute__((callback(1, 1))) void vararg_cb_2(void (*callback)(int, ...), int a); // expected-error {{'callback' attribute callee may not be variadic}}
 
-__attribute__((callback(1, -1, 1, 2, 3, 4, -1))) void varargs_1(void (*callback)(int, ...), int a, float b, double c) {}               // expected-error {{'callback' attribute requires exactly 6 arguments}}
-__attribute__((callback(1, -1, 4, 2, 3, 4, -1))) void varargs_2(void (*callback)(void *, double, int, ...), int a, float b, double c); // expected-error {{'callback' attribute requires exactly 6 arguments}}
+__attribute__((callback(1, -1, 1, 2, 3, 4, -1))) void varargs_1(void (*callback)(int, ...), int a, float b, double c) {}               // expected-error {{'callback' attribute references function of type 'void (int, ...)' which expects 1 argument but attribute specifies 6 parameter index arguments}}
+__attribute__((callback(1, -1, 4, 2, 3, 4, -1))) void varargs_2(void (*callback)(void *, double, int, ...), int a, float b, double c); // expected-error {{'callback' attribute references function of type 'void (void *, double, int, ...)' which expects 3 arguments but attribute specifies 6 parameter index arguments}}
 
-__attribute__((callback(1, -1, 1))) void self_arg_1(void (*callback)(int, ...)) {}          // expected-error {{'callback' attribute requires exactly 2 arguments}}
-__attribute__((callback(1, -1, 1, -1, -1, 1))) void self_arg_2(void (*callback)(int, ...)); // expected-error {{'callback' attribute requires exactly 5 arguments}}
+__attribute__((callback(1, -1, 1))) void self_arg_1(void (*callback)(int, ...)) {}          // expected-error {{'callback' attribute references function of type 'void (int, ...)' which expects 1 argument but attribute specifies 2 parameter index arguments}}
+__attribute__((callback(1, -1, 1, -1, -1, 1))) void self_arg_2(void (*callback)(int, ...)); // expected-error {{'callback' attribute references function of type 'void (int, ...)' which expects 1 argument but attribute specifies 5 parameter index arguments}}
 
 __attribute__((callback(cb))) void unknown_name1(void (*callback)(void)) {}     // expected-error {{'callback' attribute argument 'cb' is not a known function parameter}}
 __attribute__((callback(cb, ab))) void unknown_name2(void (*cb)(int), int a) {} // expected-error {{'callback' attribute argument 'ab' is not a known function parameter}}
 
-__attribute__((callback(callback, 1))) void too_many_args_1b(void (*callback)(void)) {}      // expected-error {{'callback' attribute takes one argument}}
-__attribute__((callback(callback, __))) void too_many_args_2b(double (*callback)(void));     // expected-error {{'callback' attribute takes one argument}}
-__attribute__((callback(callback, 2, 2))) void too_many_args_3b(void (*callback)(int), int); // expected-error {{'callback' attribute requires exactly 2 arguments}}
+__attribute__((callback(callback, 1))) void too_many_args_1b(void (*callback)(void)) {}      // expected-error-re {{'callback' attribute references function of type 'void ({{(void)?}})' which expects 0 arguments but attribute specifies 1 parameter index argument}}
+__attribute__((callback(callback, __))) void too_many_args_2b(double (*callback)(void));     // expected-error-re {{'callback' attribute references function of type 'double ({{(void)?}})' which expects 0 arguments but attribute specifies 1 parameter index argument}}
+__attribute__((callback(callback, 2, 2))) void too_many_args_3b(void (*callback)(int), int); // expected-error {{'callback' attribute references function of type 'void (int)' which expects 1 argument but attribute specifies 2 parameter index arguments}}
 
-__attribute__((callback(callback, a))) void too_few_args_1b(void (*callback)(int, int), int a); // expected-error {{'callback' attribute takes one argument}}
-__attribute__((callback(callback))) void too_few_args_2b(int (*callback)(int));                 // expected-error {{'callback' attribute takes no arguments}}
-__attribute__((callback(callback, __))) void too_few_args_3b(void (*callback)(int, int)) {}     // expected-error {{'callback' attribute takes one argument}}
+__attribute__((callback(callback, a))) void too_few_args_1b(void (*callback)(int, int), int a); // expected-error {{'callback' attribute references function of type 'void (int, int)' which expects 2 arguments but attribute specifies 1 parameter index argument}}
+__attribute__((callback(callback))) void too_few_args_2b(int (*callback)(int));                 // expected-error {{'callback' attribute references function of type 'int (int)' which expects 1 argument but attribute specifies 0 parameter index arguments}}
+__attribute__((callback(callback, __))) void too_few_args_3b(void (*callback)(int, int)) {}     // expected-error {{'callback' attribute references function of type 'void (int, int)' which expects 2 arguments but attribute specifies 1 parameter index argument}}
 
 __attribute__((callback(__))) void oob_args_1b(void (*callback)(void)); // expected-error {{'callback' attribute specifies invalid callback callee}}
 
@@ -68,8 +68,8 @@ __attribute__((callback(1, this))) void no_this_2b(void *(*callback)(int, void *
 __attribute__((callback(callback, __))) void vararg_cb_1b(void (*callback)(int, ...)) {} // expected-error {{'callback' attribute callee may not be variadic}}
 __attribute__((callback(1, a))) void vararg_cb_2b(void (*callback)(int, ...), int a);    // expected-error {{'callback' attribute callee may not be variadic}}
 
-__attribute__((callback(callback, __, callback, a, b, c, __))) void varargs_1b(void (*callback)(int, ...), int a, float b, double c) {} // expected-error {{'callback' attribute requires exactly 6 arguments}}
-__attribute__((callback(1, __, c, a, b, c, -1))) void varargs_2b(void (*callback)(void *, double, int, ...), int a, float b, double c); // expected-error {{'callback' attribute requires exactly 6 arguments}}
+__attribute__((callback(callback, __, callback, a, b, c, __))) void varargs_1b(void (*callback)(int, ...), int a, float b, double c) {} // expected-error {{'callback' attribute references function of type 'void (int, ...)' which expects 1 argument but attribute specifies 6 parameter index arguments}}
+__attribute__((callback(1, __, c, a, b, c, -1))) void varargs_2b(void (*callback)(void *, double, int, ...), int a, float b, double c); // expected-error {{'callback' attribute references function of type 'void (void *, double, int, ...)' which expects 3 arguments but attribute specifies 6 parameter index arguments}}
 
-__attribute__((callback(1, __, callback))) void self_arg_1b(void (*callback)(int, ...)) {}                        // expected-error {{'callback' attribute requires exactly 2 arguments}}
-__attribute__((callback(callback, __, callback, __, __, callback))) void self_arg_2b(void (*callback)(int, ...)); // expected-error {{'callback' attribute requires exactly 5 arguments}}
+__attribute__((callback(1, __, callback))) void self_arg_1b(void (*callback)(int, ...)) {}                        // expected-error {{'callback' attribute references function of type 'void (int, ...)' which expects 1 argument but attribute specifies 2 parameter index arguments}}
+__attribute__((callback(callback, __, callback, __, __, callback))) void self_arg_2b(void (*callback)(int, ...)); // expected-error {{'callback' attribute references function of type 'void (int, ...)' which expects 1 argument but attribute specifies 5 parameter index arguments}}