[clang] [Clang] omit parentheses in fold expressions with a single expansion (PR #110761)

[Erich Keane via cfe-commits]

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@@ -36,7 +36,7 @@ using r1i2 = r1<char>; // expected-error {{constraints not satisfied for class t
 template<typename... Ts> requires
 false_v<requires (Ts... ts) {requires ((sizeof(ts) == 2) && ...);}>
 // expected-note at -1 {{because 'false_v<requires (short ts, unsigned short ts) { requires (sizeof (ts) == 2) && (sizeof (ts) == 2); }>'}}
-// expected-note at -2 {{because 'false_v<requires (short ts) { requires (sizeof (ts) == 2); }>' evaluated to false}}
+// expected-note at -2 {{because 'false_v<requires (short ts) { requires sizeof (ts) == 2; }>' evaluated to false}}
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erichkeane wrote:

Thats the discussion we had in a separate thread, we don't really see how, without modifying the ParenExpr to say that it is the result of a fold expr expansion.

As far as 'modify the ast', depending on your perspective/mental model here, the parens are a part of the 'fold expr' rather than part of the expr being folded.  In this case, if you consider the `( ) && ...` to effectively be the fold expr syntax, removing it seems to make a ton of sense.  

But yeah, we couldn't think of a good way to suppress the warning otherwise (or, like i mentioned, a flag on `ParenExpr` to say that the `ParenExpr` is a part of a single-element-fold-expr-expansion).  The diagnostic just sees the expression after expansion, so as far as it knows, you did `if ((a == b))` instead of `if ((a==b) && ...)` but only had a single element.

https://github.com/llvm/llvm-project/pull/110761