[clang] [clang-format] Handle Trailing Whitespace After Line Continuation (P2223R2) (PR #145243)

[Björn Schäpers via cfe-commits]

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@@ -1295,13 +1305,18 @@ FormatToken *FormatTokenLexer::getNextToken() {
       case '/':
         // The text was entirely whitespace when this loop was entered. Thus
         // this has to be an escape sequence.
-        assert(Text.substr(i, 2) == "\\\r" || Text.substr(i, 2) == "\\\n" ||
-               Text.substr(i, 4) == "\?\?/\r" ||
+        assert(Text.substr(i, 4) == "\?\?/\r" ||
                Text.substr(i, 4) == "\?\?/\n" ||
                (i >= 1 && (Text.substr(i - 1, 4) == "\?\?/\r" ||
                            Text.substr(i - 1, 4) == "\?\?/\n")) ||
                (i >= 2 && (Text.substr(i - 2, 4) == "\?\?/\r" ||
-                           Text.substr(i - 2, 4) == "\?\?/\n")));
+                           Text.substr(i - 2, 4) == "\?\?/\n")) ||
+               (Text[i] == '\\' && [&]() -> bool {
+                 size_t j = i + 1;
+                 while (j < Text.size() && isHorizontalWhitespace(Text[j]))
+                   ++j;
+                 return j < Text.size() && (Text[j] == '\n' || Text[j] == '\r');
+               }()));
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HazardyKnusperkeks wrote:

The question is, why was it put there. But I have a hard time understanding it, how can `Text.substr(i, 4)` be equal to `??/\r`, when `Text[i]` is `/`?

I think an assert is fine, but it needs to be reformulated, and maybe add a comment about trigraph. I at least keep forgetting, that these things exist(ed).

https://github.com/llvm/llvm-project/pull/145243