[PATCH] D62648: [Sema][Typo] Fix assertion failure for expressions with multiple typos

Richard Smith - zygoloid via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Thu May 30 12:13:05 PDT 2019

rsmith added inline comments.

Comment at: lib/Sema/SemaExprCXX.cpp:7713-7714
+          // Add the newly created typos to the TypoExprs list, even if they
+          // failed to apply. This allows them to be reaped although they won't
+          // emit any diagnostic.
+          SavedTypoExprs.set_union(TypoExprs);
What prevents diagnostics from being emitted for `TypoExpr`s we create for an outer transform that we end up discarding? Eg, in:

struct Y {};
struct Z { int value; };
struct A {
  Y get_me_a_Y();
struct B {
  Z get_me_a_Z();
A make_an_A();
B make_a_B();
int f() {
  return make_an_E().get_me_a_Z().value;

I'm concerned that we will:
 * try correcting `make_me_an_E` (`TypoExpr` `T0`) to `make_me_an_A` (because that correction has the minimum edit distance) and discover that there is no `get_me_a_Z` member, creating a new `TypoExpr` `T1`, and recurse:
   * try correcting `get_me_a_Z` (`TypoExpr` `T1`) to `get_me_a_Y` and discover that there is no `value` member
   * no correction works: bail out of recursive step
 * try correcting `make_me_an_E` (`TypoExpr` `T0`) to `make_me_a_B` and succeed

But now we still have `T1` in our list of `TypoExpr`s, and will presumably diagnose it (and take action below if it turned out to be ambiguous etc).

Comment at: lib/Sema/SemaExprCXX.cpp:7762-7787
     // Ensure none of the TypoExprs have multiple typo correction candidates
     // with the same edit length that pass all the checks and filters.
     // TODO: Properly handle various permutations of possible corrections when
     // there is more than one potentially ambiguous typo correction.
     // Also, disable typo correction while attempting the transform when
     // handling potentially ambiguous typo corrections as any new TypoExprs will
     // have been introduced by the application of one of the correction
What happens if an ambiguous `TypoExpr` is created as a result of one of the outer level transformations?

In that case, I think that we will try alternatives for that `TypoExpr` here, but that `TypoExpr` is not in the expression we're transforming (it was created within `RecursiveTransformLoop` and isn't part of `E`), so we're just redoing the same transformation we already did but with typo-correction disabled. This means that the transform will fail (because we hit a typo and can't correct it), so we'll accept the original set of corrections despite them being ambiguous.

  rC Clang



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