[clang-tidy] fix PR36489 - respect deduced pointer types from auto as well

[JonasToth]

Summary

The cppcoreguidelines-pro-bounds-pointer-arithmetic warns on all occassion where
pointer arithmetic is used, but does not check values where the pointer types
is deduced via auto. This patch adjusts this behaviour and solved
PR36489.
I accidentally commited a wrong patch, this Differential is meant to have a
correct revision description and code attached to it.
Because the patch was accepted by aaron.ballman already, i will just commit
it.
See https://reviews.llvm.org/D48717 for the old differntial (contains wrong
code from the mixup)

[JonasToth]

rebase to master

clang-tidy/cppcoreguidelines/ProBoundsPointerArithmeticCheck.cpp

 namespace clang {
 namespace tidy {
 namespace cppcoreguidelines {
 
 void ProBoundsPointerArithmeticCheck::registerMatchers(MatchFinder *Finder) {
   if (!getLangOpts().CPlusPlus)
     return;
 
+  const auto AllPointerTypes = anyOf(
+      hasType(pointerType()), hasType(autoType(hasDeducedType(pointerType()))),
+      hasType(decltypeType(hasUnderlyingType(pointerType()))));
+
   // Flag all operators +, -, +=, -=, ++, -- that result in a pointer
   Finder->addMatcher(
       binaryOperator(
           anyOf(hasOperatorName("+"), hasOperatorName("-"),
                 hasOperatorName("+="), hasOperatorName("-=")),
-          hasType(pointerType()),
+          AllPointerTypes,
           unless(hasLHS(ignoringImpCasts(declRefExpr(to(isImplicit()))))))
           .bind("expr"),
       this);
 
   Finder->addMatcher(
       unaryOperator(anyOf(hasOperatorName("++"), hasOperatorName("--")),
                     hasType(pointerType()))
           .bind("expr"),
       this);
 
   // Array subscript on a pointer (not an array) is also pointer arithmetic
   Finder->addMatcher(
       arraySubscriptExpr(
           hasBase(ignoringImpCasts(
-              anyOf(hasType(pointerType()),
+              anyOf(AllPointerTypes,
                     hasType(decayedType(hasDecayedType(pointerType())))))))
           .bind("expr"),
       this);
 }
 
 void ProBoundsPointerArithmeticCheck::check(
     const MatchFinder::MatchResult &Result) {
   const auto *MatchedExpr = Result.Nodes.getNodeAs<Expr>("expr");
 
   diag(MatchedExpr->getExprLoc(), "do not use pointer arithmetic");
 }
 
 } // namespace cppcoreguidelines
 } // namespace tidy
 } // namespace clang

test/clang-tidy/cppcoreguidelines-pro-bounds-pointer-arithmetic-pr36489.cpp

+// RUN: %check_clang_tidy %s cppcoreguidelines-pro-bounds-pointer-arithmetic %t -- -- -std=c++14
+
+// Fix PR36489 and detect auto-deduced value correctly.
+char *getPtr();
+auto getPtrAuto() { return getPtr(); }
+decltype(getPtr()) getPtrDeclType();
+decltype(auto) getPtrDeclTypeAuto() { return getPtr(); }
+auto getPtrWithTrailingReturnType() -> char *;
+
+void auto_deduction_binary() {
+  auto p1 = getPtr() + 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:22: warning: do not use pointer arithmetic
+  auto p2 = getPtrAuto() + 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:26: warning: do not use pointer arithmetic
+  auto p3 = getPtrWithTrailingReturnType() + 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:44: warning: do not use pointer arithmetic
+  auto p4 = getPtr();
+  auto *p5 = getPtr();
+  p4 = p4 + 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: do not use pointer arithmetic
+  p5 = p5 + 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: do not use pointer arithmetic
+  auto p6 = getPtrDeclType() + 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:30: warning: do not use pointer arithmetic
+  auto p7 = getPtrDeclTypeAuto() + 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:34: warning: do not use pointer arithmetic
+  auto *p8 = getPtrDeclType() + 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:31: warning: do not use pointer arithmetic
+  auto *p9 = getPtrDeclTypeAuto() + 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:35: warning: do not use pointer arithmetic
+}
+
+void auto_deduction_subscript() {
+  char p1 = getPtr()[2];
+  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use pointer arithmetic
+  auto p2 = getPtr()[3];
+  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use pointer arithmetic
+
+  char p3 = getPtrAuto()[4];
+  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use pointer arithmetic
+  auto p4 = getPtrAuto()[5];
+  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use pointer arithmetic
+
+  char p5 = getPtrWithTrailingReturnType()[6];
+  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use pointer arithmetic
+  auto p6 = getPtrWithTrailingReturnType()[7];
+  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use pointer arithmetic
+
+  auto p7 = getPtrDeclType()[8];
+  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use pointer arithmetic
+  auto p8 = getPtrDeclTypeAuto()[9];
+  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use pointer arithmetic
+}