[AutoDiff] Improve @derivative and @transpose diagnostics. (#32717)

Improve `@derivative` and `@transpose` type-checking diagnostics for resolving
the referenced original declaration.

Previously, an error was produced on one invalid candidate at the attribute's
location. This did not indicate the invalid candidate's location or the total
number of invalid candidates.

Now:
- Diagnostic notes are produced on all invalid candidates at their location.
  Invalid candidates' descriptive declaration kind are shown for clarity.
- Derivative registration for protocol requirements (not yet supported, TF-982)
  now has a clear, dedicated diagnostic.
- The "original declaration type mismatch" diagnostic is improved for expected
  original function types with generic signatures. The message now accurately
  reads "candidate does not have type equal to *or less constrained than* ...",
  instead of "candidate does not have expected type ...".

Resolves SR-13150.
Paves the way for future diagnostic improvements: SR-13151, SR-13152.

Author: dan-zheng

include/swift/AST/DiagnosticsSema.def

@@ -3095,10 +3095,16 @@ ERROR(derivative_attr_class_member_dynamic_self_result_unsupported,none,
 ERROR(derivative_attr_nonfinal_class_init_unsupported,none,
       "cannot register derivative for 'init' in a non-final class; consider "
       "making %0 final", (Type))
+ERROR(derivative_attr_unsupported_accessor_kind,none,
+      "cannot register derivative for %0", (/*accessorKind*/ DescriptiveDeclKind))
 // TODO(SR-13096): Remove this temporary diagnostic.
 ERROR(derivative_attr_class_setter_unsupported,none,
       "cannot yet register derivative for class property or subscript setters",
       ())
+// TODO(TF-982): Remove this temporary diagnostic.
+NOTE(derivative_attr_protocol_requirement_unsupported,none,
+     "cannot yet register derivative default implementation for protocol "
+     "requirements", ())
 ERROR(derivative_attr_original_already_has_derivative,none,
       "a derivative already exists for %0", (DeclName))
 NOTE(derivative_attr_duplicate_note,none,
@@ -3134,15 +3140,25 @@ NOTE(transpose_attr_wrt_self_self_type_mismatch_note,none,
      "%1", (Type, Type))
 
 // Automatic differentiation attributes
-ERROR(autodiff_attr_original_decl_invalid_kind,none,
-      "%0 is not a 'func', 'init', 'subscript', or 'var' computed property "
-      "declaration", (DeclNameRef))
-ERROR(autodiff_attr_accessor_not_found,none,
-      "%0 does not have a '%1' accessor", (DeclNameRef, StringRef))
-ERROR(autodiff_attr_original_decl_none_valid_found,none,
-      "could not find function %0 with expected type %1", (DeclNameRef, Type))
-ERROR(autodiff_attr_original_decl_not_same_type_context,none,
-      "%0 is not defined in the current type context", (DeclNameRef))
+ERROR(autodiff_attr_original_decl_ambiguous,none,
+      "referenced declaration %0 is ambiguous", (DeclNameRef))
+NOTE(autodiff_attr_original_decl_ambiguous_candidate,none,
+     "candidate %0 found here", (DescriptiveDeclKind))
+ERROR(autodiff_attr_original_decl_none_valid,none,
+      "referenced declaration %0 could not be resolved", (DeclNameRef))
+NOTE(autodiff_attr_original_decl_invalid_kind,none,
+     "candidate %0 is not a 'func', 'init', 'subscript', or 'var' computed "
+     "property declaration", (DescriptiveDeclKind))
+NOTE(autodiff_attr_original_decl_missing_accessor,none,
+     "candidate %0 does not have a %1",
+     (DescriptiveDeclKind, /*accessorDeclKind*/ DescriptiveDeclKind))
+NOTE(autodiff_attr_original_decl_type_mismatch,none,
+     "candidate %0 does not have "
+     "%select{expected type|type equal to or less constrained than}2 %1",
+     (DescriptiveDeclKind, Type, /*hasGenericSignature*/ bool))
+NOTE(autodiff_attr_original_decl_not_same_type_context,none,
+     "candidate %0 is not defined in the current type context",
+     (DescriptiveDeclKind))
 ERROR(autodiff_attr_original_void_result,none,
       "cannot differentiate void function %0", (DeclName))
 ERROR(autodiff_attr_original_multiple_semantic_results,none,