[clang] [Clang] Wide delimiters ('{{{') for expect strings (PR #77326)

[via cfe-commits]

https://github.com/sethp created https://github.com/llvm/llvm-project/pull/77326

Prior to this commit, it was impossible to use the simple string matching directives to look for most content that contains `{{`, such as:

```
// expected-note {{my_struct{{1}, 2}}}
```

Which would parse like so:

```
             "nested" brace v
// expected-note {{my_struct{{1}, 2}}}
          closes the nested brace  ^ |
                            trailing }
```

And the frontend would complain 'cannot find end ('}}') of expected'.

At this snapshot, VerifyDiagnosticConsumer's parser now counts the opening braces and looks for a matching length of closing sigils, allowing the above to be written as:

```
// expected-note {{{my_struct{{1}, 2}}}}
   opening brace |-|                 |-|
  closing brace is '}}}', found here ^
```

This came about as a result of this discussion: https://github.com/llvm/llvm-project/pull/74852#discussion_r1443117644

cc @erichkeane 

>From cd0b9aed2d9e53f9b38aaa0f73336acae06bfbee Mon Sep 17 00:00:00 2001
From: Seth Pellegrino <seth at codecopse.net>
Date: Sat, 6 Jan 2024 07:54:31 -0800
Subject: [PATCH] [Clang] Wide delimiters ('{{{') for expect strings

Prior to this commit, it was impossible to use the simple string
matching directives to look for most content that contains `{{`, such
as:

```
// expected-note {{my_struct{{1}, 2}}}
```

Which would parse like so:

```
             "nested" brace v
// expected-note {{my_struct{{1}, 2}}}
          closes the nested brace  ^ |
                            trailing }
```

And the frontend would complain 'cannot find end ('}}') of expected'.

At this snapshot, VerifyDiagnosticConsumer's parser now counts the
opening braces and looks for a matching length of closing sigils,
allowing the above to be written as:

```
// expected-note {{{my_struct{{1}, 2}}}}
   opening brace |-|                 |-|
  closing brace is '}}}', found here ^
```
---
 .../clang/Basic/DiagnosticFrontendKinds.td        |  2 +-
 clang/lib/Frontend/VerifyDiagnosticConsumer.cpp   | 15 +++++++++++----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/clang/include/clang/Basic/DiagnosticFrontendKinds.td b/clang/include/clang/Basic/DiagnosticFrontendKinds.td
index 715e0c0dc8fa84..4bf0ab54a046c1 100644
--- a/clang/include/clang/Basic/DiagnosticFrontendKinds.td
+++ b/clang/include/clang/Basic/DiagnosticFrontendKinds.td
@@ -166,7 +166,7 @@ def err_verify_no_such_marker : Error<
 def err_verify_missing_start : Error<
     "cannot find start ('{{') of expected %0">;
 def err_verify_missing_end : Error<
-    "cannot find end ('}}') of expected %0">;
+    "cannot find end ('%1') of expected %0">;
 def err_verify_invalid_content : Error<
     "invalid expected %0: %1">;
 def err_verify_missing_regex : Error<
diff --git a/clang/lib/Frontend/VerifyDiagnosticConsumer.cpp b/clang/lib/Frontend/VerifyDiagnosticConsumer.cpp
index ab8174f4f4db92..5eab7bd3619f19 100644
--- a/clang/lib/Frontend/VerifyDiagnosticConsumer.cpp
+++ b/clang/lib/Frontend/VerifyDiagnosticConsumer.cpp
@@ -612,12 +612,19 @@ static bool ParseDirective(StringRef S, ExpectedData *ED, SourceManager &SM,
                    diag::err_verify_missing_start) << KindStr;
       continue;
     }
+    llvm::SmallString<8> CloseBrace("}}");
+    const char *const DelimBegin = PH.C;
     PH.Advance();
+    // Count the number of opening braces for `string` kinds
+    for (; !D.RegexKind && PH.Next("{"); PH.Advance())
+      CloseBrace += '}';
     const char* const ContentBegin = PH.C; // mark content begin
-    // Search for token: }}
-    if (!PH.SearchClosingBrace("{{", "}}")) {
-      Diags.Report(Pos.getLocWithOffset(PH.C-PH.Begin),
-                   diag::err_verify_missing_end) << KindStr;
+    // Search for closing brace
+    StringRef OpenBrace(DelimBegin, ContentBegin - DelimBegin);
+    if (!PH.SearchClosingBrace(OpenBrace, CloseBrace)) {
+      Diags.Report(Pos.getLocWithOffset(PH.C - PH.Begin),
+                   diag::err_verify_missing_end)
+          << KindStr << CloseBrace;
       continue;
     }
     const char* const ContentEnd = PH.P; // mark content end