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[Sema][Typo Correction] Fix potential infite loop on ambiguity checks

Summary:
This fixes a bug introduced in D62648, where Clang could infinite loop
if it became stuck on a single TypoCorrection when it was supposed to
be testing ambiguous corrections. Although not a common case, it could
happen if there are multiple possible corrections with the same edit
distance.

The fix is simply to wipe the TypoExpr from the `TransformCache` so that
the call to `TransformTypoExpr` doesn't use the `CachedEntry`.

Reviewers: rsmith

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67515

llvm-svn: 371859
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DavidGoldman committed Sep 13, 2019
1 parent e7e8b51 commit 6d186504216446a1620628057c10bddb9b0b9085
Showing with 33 additions and 0 deletions.
  1. +4 −0 clang/lib/Sema/SemaExprCXX.cpp
  2. +29 −0 clang/test/Sema/typo-correction-ambiguity.cpp
@@ -7755,6 +7755,10 @@ class TransformTypos : public TreeTransform<TransformTypos> {
TypoCorrection TC = SemaRef.getTypoExprState(TE).Consumer->peekNextCorrection();
TypoCorrection Next;
do {
// Fetch the next correction by erasing the typo from the cache and calling
// `TryTransform` which will iterate through corrections in
// `TransformTypoExpr`.
TransformCache.erase(TE);
ExprResult AmbigRes = CheckForRecursiveTypos(TryTransform(E), IsAmbiguous);

if (!AmbigRes.isInvalid() || IsAmbiguous) {
@@ -0,0 +1,29 @@
// RUN: %clang_cc1 -fsyntax-only -verify %s

// Check the following typo correction behavior in namespaces:
// - no typos are diagnosed when an expression has ambiguous (multiple) corrections
// - proper iteration through multiple potentially ambiguous corrections

namespace AmbiguousCorrection
{
void method_Bar();
void method_Foo();
void method_Zoo();
};

void testAmbiguousNoSuggestions()
{
AmbiguousCorrection::method_Ace(); // expected-error {{no member named 'method_Ace' in namespace 'AmbiguousCorrection'}}
}

namespace MultipleCorrectionsButNotAmbiguous
{
int PrefixType_Name(int value); // expected-note {{'PrefixType_Name' declared here}}
int PrefixType_MIN();
int PrefixType_MAX();
};

int testMultipleCorrectionsButNotAmbiguous() {
int val = MultipleCorrectionsButNotAmbiguous::PrefixType_Enum(0); // expected-error {{no member named 'PrefixType_Enum' in namespace 'MultipleCorrectionsButNotAmbiguous'; did you mean 'PrefixType_Name'?}}
return val;
}

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