Revert "[clang] Fix-it hint for ++this -> ++*this when deref is modifiable" (#95833)

Reverts #94159

@zygoloid had some concerns about the implementation of this, which make
sense to me, so I’d like to revert this for now so we can have more time
to think about how to best approach this (if at all...)

Author: Sirraide

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -8778,9 +8778,6 @@ def err_typecheck_incomplete_type_not_modifiable_lvalue : Error<
 def err_typecheck_lvalue_casts_not_supported : Error<
   "assignment to cast is illegal, lvalue casts are not supported">;
 
-def note_typecheck_add_deref_star_not_modifiable_lvalue : Note<
-  "add '*' to dereference it">; 
-
 def err_typecheck_duplicate_vector_components_not_mlvalue : Error<
   "vector is not assignable (contains duplicate components)">;
 def err_block_decl_ref_not_modifiable_lvalue : Error<

clang/lib/Sema/SemaExpr.cpp

@@ -13288,23 +13288,6 @@ enum {
   ConstUnknown,  // Keep as last element
 };
 
-static void MaybeSuggestDerefFixIt(Sema &S, const Expr *E, SourceLocation Loc) {
-  ExprResult Deref;
-  Expr *TE = const_cast<Expr *>(E);
-  {
-    Sema::TentativeAnalysisScope Trap(S);
-    Deref = S.ActOnUnaryOp(S.getCurScope(), Loc, tok::star, TE);
-  }
-  if (Deref.isUsable() &&
-      Deref.get()->isModifiableLvalue(S.Context, &Loc) == Expr::MLV_Valid &&
-      !E->getType()->isObjCObjectPointerType()) {
-    S.Diag(E->getBeginLoc(),
-           diag::note_typecheck_add_deref_star_not_modifiable_lvalue)
-        << E->getSourceRange()
-        << FixItHint::CreateInsertion(E->getBeginLoc(), "*");
-  }
-}
-
 /// Emit the "read-only variable not assignable" error and print notes to give
 /// more information about why the variable is not assignable, such as pointing
 /// to the declaration of a const variable, showing that a method is const, or
@@ -13399,7 +13382,6 @@ static void DiagnoseConstAssignment(Sema &S, const Expr *E,
         if (!DiagnosticEmitted) {
           S.Diag(Loc, diag::err_typecheck_assign_const)
               << ExprRange << ConstVariable << VD << VD->getType();
-          MaybeSuggestDerefFixIt(S, E, Loc);
           DiagnosticEmitted = true;
         }
         S.Diag(VD->getLocation(), diag::note_typecheck_assign_const)
@@ -13620,12 +13602,10 @@ static bool CheckForModifiableLvalue(Expr *E, SourceLocation Loc, Sema &S) {
   SourceRange Assign;
   if (Loc != OrigLoc)
     Assign = SourceRange(OrigLoc, OrigLoc);
-  if (NeedType) {
+  if (NeedType)
     S.Diag(Loc, DiagID) << E->getType() << E->getSourceRange() << Assign;
-  } else {
+  else
     S.Diag(Loc, DiagID) << E->getSourceRange() << Assign;
-    MaybeSuggestDerefFixIt(S, E, Loc);
-  }
   return true;
 }
 

clang/test/C/drs/dr1xx.c

@@ -296,7 +296,6 @@ void dr126(void) {
    */
   *object = 12; /* ok */
   ++object; /* expected-error {{cannot assign to variable 'object' with const-qualified type 'const IP' (aka 'int *const')}} */
-  /* expected-note@-1 {{add '*' to dereference it}} */
 }
 
 /* WG14 DR128: yes

clang/test/Sema/debug-93066.cpp

@@ -65,10 +65,8 @@ void test4(void) {
 
 void test5(int *X, float *P) {
   (float*)X = P;   // expected-error {{assignment to cast is illegal, lvalue casts are not supported}}
-  // expected-note@-1 {{add '*' to dereference it}}
 #define FOO ((float*) X)
   FOO = P;   // expected-error {{assignment to cast is illegal, lvalue casts are not supported}}
-  // expected-note@-1 {{add '*' to dereference it}}
 }
 
 void test6(void) {

clang/test/Sema/exprs.c

@@ -2,6 +2,5 @@
 
 int a(void) {
   __builtin_va_arg((char*)0, int); // expected-error {{expression is not assignable}}
-  // expected-note@-1 {{add '*' to dereference it}}
   __builtin_va_arg((void*){0}, int); // expected-error {{first argument to 'va_arg' is of type 'void *'}}
 }

clang/test/Sema/va_arg_x86_32.c

@@ -9,20 +9,7 @@ void h() {
   SEL s = @selector(dealloc);
   SEL* ps = &s;
 
-  /*
-   FIXME: https://github.com/llvm/llvm-project/pull/94159
-   
-   TLDR; This is about inserting '*' to deref.
-   
-   This would assign the value of s to the SEL object pointed to by
-   @selector(dealloc). However, in Objective-C, selectors are not pointers,
-   they are special compile-time constructs representing method names, and
-   they are immutable, so you cannot assign values to them.
-
-   Therefore, this syntax is not valid for selectors in Objective-C.
-   */
   @selector(dealloc) = s;  // expected-error {{expression is not assignable}}
-  // expected-note@-1 {{add '*' to dereference it}}
 
   SEL* ps2 = &@selector(dealloc);