Fix OOM in FormatDiagnostic (#108187)

Resolves: #70930 (and probably latest comments from
https://github.com/clangd/clangd/issues/251)
by fixing racing for the shared `DiagStorage` value which caused messing
with args inside the storage and then formatting the following message
with `getArgSInt(1)` == 2:
```
def err_module_odr_violation_function : Error<
  "%q0 has different definitions in different modules; "
  "%select{definition in module '%2'|defined here}1 "
  "first difference is "
```
which causes `HandleSelectModifier` to go beyond the `ArgumentLen` so
the recursive call to `FormatDiagnostic` was made with `DiagStr` >
`DiagEnd` that leads to infinite `while (DiagStr != DiagEnd)`.

**The Main Idea:**
Reuse the existing `DiagStorageAllocator` logic to make all
`DiagnosticBuilder`s having independent states.
Also, encapsulating the rest of state (e.g. ID and Loc) into
`DiagnosticBuilder`.

**TODO (if it will be requested by reviewer):**
- [x] add a test (I have no idea how to turn a whole bunch of my
proprietary code which leads `clangd` to OOM into a small public
example.. probably I must try using
[this](https://github.com/llvm/llvm-project/issues/70930#issuecomment-2209872975)
instead)
- [x] [`Diag.CurDiagID !=
diag::fatal_too_many_errors`](https://github.com/llvm/llvm-project/pull/108187#pullrequestreview-2296395489)
- [ ] ? get rid of `DiagStorageAllocator` at all and make
`DiagnosticBuilder` having they own `DiagnosticStorage` coz it seems
pretty small so should fit the stack for short-living
`DiagnosticBuilder` instances

1 files changed, 4 insertions, 19 deletions

diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index d6ec26a..65a8a72 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -130,13 +130,8 @@ ContentCache::getBufferOrNone(DiagnosticsEngine &Diag, FileManager &FM,
   // the file could also have been removed during processing. Since we can't
   // really deal with this situation, just create an empty buffer.
   if (!BufferOrError) {
-    if (Diag.isDiagnosticInFlight())
-      Diag.SetDelayedDiagnostic(diag::err_cannot_open_file,
-                                ContentsEntry->getName(),
-                                BufferOrError.getError().message());
-    else
-      Diag.Report(Loc, diag::err_cannot_open_file)
-          << ContentsEntry->getName() << BufferOrError.getError().message();
+    Diag.Report(Loc, diag::err_cannot_open_file)
+        << ContentsEntry->getName() << BufferOrError.getError().message();
 
     return std::nullopt;
   }
@@ -153,12 +148,7 @@ ContentCache::getBufferOrNone(DiagnosticsEngine &Diag, FileManager &FM,
   // ContentsEntry::getSize() could have the wrong size. Use
   // MemoryBuffer::getBufferSize() instead.
   if (Buffer->getBufferSize() >= std::numeric_limits<unsigned>::max()) {
-    if (Diag.isDiagnosticInFlight())
-      Diag.SetDelayedDiagnostic(diag::err_file_too_large,
-                                ContentsEntry->getName());
-    else
-      Diag.Report(Loc, diag::err_file_too_large)
-        << ContentsEntry->getName();
+    Diag.Report(Loc, diag::err_file_too_large) << ContentsEntry->getName();
 
     return std::nullopt;
   }
@@ -168,12 +158,7 @@ ContentCache::getBufferOrNone(DiagnosticsEngine &Diag, FileManager &FM,
   // have come from a stat cache).
   if (!ContentsEntry->isNamedPipe() &&
       Buffer->getBufferSize() != (size_t)ContentsEntry->getSize()) {
-    if (Diag.isDiagnosticInFlight())
-      Diag.SetDelayedDiagnostic(diag::err_file_modified,
-                                ContentsEntry->getName());
-    else
-      Diag.Report(Loc, diag::err_file_modified)
-        << ContentsEntry->getName();
+    Diag.Report(Loc, diag::err_file_modified) << ContentsEntry->getName();
 
     return std::nullopt;
   }