[PATCH] D146764: [clang] Make predefined expressions string literals under -fms-extensions

[Arthur Eubanks (out until mid-April) via Phabricator via cfe-commits]

aeubanks added inline comments.


================
Comment at: clang/lib/Sema/SemaExpr.cpp:3586-3591
+  // MSVC treats all predefined expressions as string literals rather than char
+  // arrays.
+  if (LangOpts.MicrosoftExt)
+    return SL;
+
   return PredefinedExpr::Create(Context, Loc, ResTy, IK, SL);
----------------
cor3ntin wrote:
> aaron.ballman wrote:
> > aeubanks wrote:
> > > aaron.ballman wrote:
> > > > This is incorrect -- these are still predefined expressions even if they're a string literal. Otherwise, we lose AST fidelity and things like the `predefinedExpr()` AST matcher don't work (https://github.com/llvm/llvm-project/blob/main/clang/include/clang/ASTMatchers/ASTMatchers.h#L2697), and `-ast-print` will print the wrong thing (https://github.com/llvm/llvm-project/blob/main/clang/lib/AST/StmtPrinter.cpp#L1248).
> > > how would you structure this? an almost identical `PredefinedExpr` class that also subclasses `StringLiteral`? or special case all the places that check for `StringLiteral` to also check for `PredefinedExpr` (the case I was mostly looking at was initializing a char array with predefined expressions but presumably there are more places that matter)
> > We can't inherit from `StringLiteral` (it's a `final` class because it has `TrailingObjects`), so that might be the only viable approach. However, there's a fair number of places in the compiler where we care if something is or isn't a `StringLiteral`, so I can see why we'd want to avoid that if possible.
> > 
> > Oye, but it seems that even MSVC is not consistent with whether the predefined expression is a string literal or not: https://godbolt.org/z/jzY8cz79d
> I think these should be plain old string literals, but for the purpose or AST matchers and such, maybe we could have a "predefined macro" bit, or even an additional object that stores the name.
> Oye, but it seems that even MSVC is not consistent with whether the predefined expression is a string literal or not: https://godbolt.org/z/jzY8cz79d

the other predefined expressions work, that looks like a bug on MSVC's part

> I think these should be plain old string literals, but for the purpose or AST matchers and such, maybe we could have a "predefined macro" bit, or even an additional object that stores the name.

what do you mean by "an additional object that stores the name"?

I started trying to add a bit to `StringLiteral` that signifies if it's an MSVC predefined expression. being new to ast matchers, I'm having trouble figuring out how to make a matcher that matches both `PredefinedExpr` and some `StringLiteral`s but also behaves like a `VariadicDynCastAllOfMatcher`.

something I noticed in one of the tests [1] is that there's a check
```
predefinedExpr(hasType(asString("const char[4]")),
                                     has(stringLiteral()))
```
thinking about the `has(stringLiteral())`, if somebody wants to get the literal for a predefined expr, presumably right now they're looking for a string literal child, but if we directly match a string literal then that would break? WDYT?

[1] https://github.com/llvm/llvm-project/blob/75ca15fcbb2e1b3671e41f971a000c6d59f5e5ae/clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp#L1064


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  https://reviews.llvm.org/D146764/new/

https://reviews.llvm.org/D146764