[clang] [Clang] Fix assertion failure in getASTRecordLayout for invalid declarations (PR #208153)

[Aditi Medhane via cfe-commits]

https://github.com/AditiRM created https://github.com/llvm/llvm-project/pull/208153

When encountering invalid declarations during error recovery (e.g., explicit template specialization after instantiation), `getASTRecordLayout()` would assert and crash instead of handling the error gracefully.

This patch adds a check for invalid/incomplete declarations and returns a minimal safe layout (1-byte size/alignment) to allow error recovery to continue, enabling the compiler to report all errors and exit cleanly.

Before this fix:
- Assertion failed: `!D->isInvalidDecl()`
- Exit code: 134 (SIGABRT)

After this fix:
- Clean error messages
- Exit code: 1

Test updated: `clang/test/SemaCXX/explicit-specialization-after-instantiation-crash.cpp`
Addresses this issue : https://github.com/llvm/llvm-project/issues/207953

>From fc5b255d45e83e441bee668a95e6d10b28d81d5e Mon Sep 17 00:00:00 2001
From: AditiRM <aditimedhane73 at gmail.com>
Date: Wed, 8 Jul 2026 07:09:35 +0000
Subject: [PATCH] [Clang] Fix assertion failure in getASTRecordLayout

---
 clang/lib/AST/RecordLayoutBuilder.cpp | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 854f88f20b2b6..15fe6e85be7ed 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -3384,6 +3384,32 @@ ASTContext::getASTRecordLayout(const RecordDecl *D) const {
   // not a complete definition (which is what isCompleteDefinition() tests)
   // until we *finish* parsing the definition.
   D = D->getDefinition();
+  
+  // Handle invalid declarations gracefully during error recovery
+  // This can happen when there are template specialization errors
+  if (!D || D->isInvalidDecl() || !D->isCompleteDefinition()) {
+    // Check if we already have a cached layout
+    const ASTRecordLayout *Entry = ASTRecordLayouts[D];
+    if (Entry)
+      return *Entry;
+    
+    // Create a minimal safe layout for error recovery
+    // Use 1-byte size and alignment to avoid division by zero or other issues
+    ASTRecordLayout *NewEntry = new (*this) ASTRecordLayout(
+        *this,
+        CharUnits::One(),      // Size = 1 byte
+        CharUnits::One(),      // Alignment = 1 byte
+        CharUnits::One(),      // PreferredAlignment = 1 byte
+        CharUnits::One(),      // UnadjustedAlignment = 1 byte
+        CharUnits::One(),      // RequiredAlignment = 1 byte
+        CharUnits::One(),      // DataSize = 1 byte
+        ArrayRef<uint64_t>()   // Empty field offsets
+    );
+    
+    ASTRecordLayouts[D] = NewEntry;
+    return *NewEntry;
+  }
+
   assert(D && "Cannot get layout of forward declarations!");
   assert(!D->isInvalidDecl() && "Cannot get layout of invalid decl!");
   assert(D->isCompleteDefinition() && "Cannot layout type before complete!");