[PATCH] D82954: Fix crash on overloaded postfix unary operators due to invalid SourceLocation

[Eduardo Caldas via Phabricator via cfe-commits]

eduucaldas added a comment.





================
Comment at: clang/lib/Tooling/Syntax/BuildTree.cpp:741
   bool WalkUpFromIntegerLiteral(IntegerLiteral *S) {
+    if (S->getLocation().isInvalid())
+      return true;
----------------
gribozavr2 wrote:
> WDYT about overriding `TraverseCXXOperatorCallExpr`, so that we don't even visit the synthetic argument of the postfix unary `++`? I would prefer to not introduce blanket "if invalid then ignore" checks in the code.
>>! In D82954#2125300, @eduucaldas wrote:
> [[ https://godbolt.org/z/CWVEJ2 | Code that reproduces the crash ]]
> Notice that when using a postfix unary operator ++ one argument is introduced to differ it from its prefix counterpart, but that argument is not used. This phantom argument shows up in the ClangAST in the form of an `IntegerLiteral` with `invalid sloc`. This invalid sloc in a valid AST node was causing the SyntaxTree generation to crash.
> We can address this problems at two different levels:
> 1. At the `TraverseCXXOperatorCallExpr`, by overriding it and replacing the children iteration to not iterate over this phantom argument.
> 2. At the `WalkUpFromIntegerLiteral`, by skipping the visitation of the phantom node.
> We preferred the latter.
> 1. Cons: We would have to duplicate the implementation of RecursiveASTVisitor in BuildTree, to handle this subtle change in traversal. That would add code complexity.
> 2. Cons: We are handling a problem of `CXXOperatorCallExpr` in `IntegerLiteral`. 
> 
> We chose the latter as, anyways, if an AST node has an invalid sloc, it was either a problem with parsing or the node is supposed to be ignored

I've explained my reasoning in my first comment for this patch. But as it was a long time ago, I guess it got lost, even by me.
 
I'll sketch how the Traverse solution would look like, to be able to give more concrete arguments.


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Comment at: clang/unittests/Tooling/Syntax/TreeTest.cpp:2376
+    | | |   `-x
+    | | `-IdExpression
+    | |   `-UnqualifiedId
----------------
gribozavr2 wrote:
> I'm not sure about this part where `++` is wrapped in IdExpression -- shouldn't the syntax tree look identical to a builtin postfix `++` (see another test in this file)?
This comes back to a discussion we had a month ago about operators ( `+`, `!`, etc)
**Question**: Should we represent operators (built-in or overloaded) in the syntax tree uniformly? If so in which way?
**Context**: The ClangAST stores built-in operators as mere tokens, whereas overloaded operators are represented as a `DeclRefExpr`. That makes a lot of sense for the ClangAST, as we might refer back to the declaration of the overloaded operator, but the declaration of built-in operator doesn't exist.
**Conclusion**: Have the same representation for both types of operators. I have implemented the "unboxed" representation of overloaded operators, i.e. just storing their token in the syntax tree. I have not committed that, but I can do it just after this patch.


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