Auto merge of #132549 - Zalathar:rust-string, r=cuviper

Make `RustString` an extern type to avoid `improper_ctypes` warnings

Currently, any FFI function that uses `&RustString` needs to also add `#[ignore(improper_ctypes)]` to silence a warning.

The warning is not _completely_ bogus, because `RustString` contains `Vec<u8>` and therefore does not have a guaranteed layout. But we have no way of telling the lint that this doesn't matter, because the C++ code only uses that pointer opaquely and never relies on its underlying layout.

Ideally there would be some way to silence `improper_ctypes` at the type-definition site. But because there isn't, casting to and from a separate extern type is better than having to annotate every single use site.

3 files changed, 7 insertions, 5 deletions

diff --git a/compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h b/compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h
index 73bbc9de855..76f7d054040 100644
--- a/compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h
+++ b/compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h
@@ -104,8 +104,9 @@ typedef struct OpaqueRustString *RustStringRef;
 typedef struct LLVMOpaqueTwine *LLVMTwineRef;
 typedef struct LLVMOpaqueSMDiagnostic *LLVMSMDiagnosticRef;
 
-extern "C" void LLVMRustStringWriteImpl(RustStringRef Str, const char *Ptr,
-                                        size_t Size);
+extern "C" void LLVMRustStringWriteImpl(RustStringRef buf,
+                                        const char *slice_ptr,
+                                        size_t slice_len);
 
 class RawRustStringOstream : public llvm::raw_ostream {
   RustStringRef Str;
diff --git a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
index eb99d560e57..6f47ee88add 100644
--- a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
@@ -1624,5 +1624,6 @@ extern "C" void LLVMRustComputeLTOCacheKey(RustStringRef KeyOut,
                            CfiFunctionDefs, CfiFunctionDecls);
 #endif
 
-  LLVMRustStringWriteImpl(KeyOut, Key.c_str(), Key.size());
+  auto OS = RawRustStringOstream(KeyOut);
+  OS << Key.str();
 }
diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index a68eed03e61..f739b010c30 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
@@ -1510,8 +1510,8 @@ LLVMRustUnpackSMDiagnostic(LLVMSMDiagnosticRef DRef, RustStringRef MessageOut,
   const SourceMgr &LSM = *D.getSourceMgr();
   const MemoryBuffer *LBuf =
       LSM.getMemoryBuffer(LSM.FindBufferContainingLoc(D.getLoc()));
-  LLVMRustStringWriteImpl(BufferOut, LBuf->getBufferStart(),
-                          LBuf->getBufferSize());
+  auto BufferOS = RawRustStringOstream(BufferOut);
+  BufferOS << LBuf->getBuffer();
 
   *LocOut = D.getLoc().getPointer() - LBuf->getBufferStart();