[Lldb-commits] [lldb] [lldb] Fix crash when adding members to an "incomplete" type (PR #102116)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Pavel Labath (labath)

<details>
<summary>Changes</summary>

This fixes a regression caused by delayed type definition searching (#<!-- -->96755 and friends): If we end up adding a member (e.g. a typedef) to a type that we've already attempted to complete (and failed), the resulting AST would end up inconsistent (we would start to "forcibly" complete it, but never finish it), and importing it into an expression AST would crash.

This patch fixes this by detecting the situation and finishing the definition as well.

---
Full diff: https://github.com/llvm/llvm-project/pull/102116.diff


2 Files Affected:

- (modified) lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp (+9-2) 
- (added) lldb/test/Shell/SymbolFile/DWARF/x86/typedef-in-incomplete-type.cpp (+23) 


``````````diff
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
index a4dcde1629fc2..3968d5bf71e1c 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
@@ -269,8 +269,15 @@ static void PrepareContextToReceiveMembers(TypeSystemClang &ast,
   }
 
   // We don't have a type definition and/or the import failed, but we need to
-  // add members to it. Start the definition to make that possible.
-  tag_decl_ctx->startDefinition();
+  // add members to it. Start the definition to make that possible. If the type
+  // has no external storage we also have to complete the definition. Otherwise,
+  // that will happen when we are asked to complete the type
+  // (CompleteTypeFromDWARF).
+  ast.StartTagDeclarationDefinition(type);
+  if (!tag_decl_ctx->hasExternalLexicalStorage()) {
+    ast.SetDeclIsForcefullyCompleted(tag_decl_ctx);
+    ast.CompleteTagDeclarationDefinition(type);
+  }
 }
 
 ParsedDWARFTypeAttributes::ParsedDWARFTypeAttributes(const DWARFDIE &die) {
diff --git a/lldb/test/Shell/SymbolFile/DWARF/x86/typedef-in-incomplete-type.cpp b/lldb/test/Shell/SymbolFile/DWARF/x86/typedef-in-incomplete-type.cpp
new file mode 100644
index 0000000000000..47ea1e2639c6e
--- /dev/null
+++ b/lldb/test/Shell/SymbolFile/DWARF/x86/typedef-in-incomplete-type.cpp
@@ -0,0 +1,23 @@
+// RUN: %clangxx --target=x86_64-pc-linux -o %t -c %s -g
+// RUN: %lldb %t -o "target var a" -o "expr -- var" -o exit | FileCheck %s
+
+// This forces lldb to attempt to complete the type A. Since it has no
+// definition it will fail.
+// CHECK: target var a
+// CHECK: (A) a = <incomplete type "A">
+
+// Now attempt to display the second variable, which will try to add a typedef
+// to the incomplete type. Make sure that succeeds. Use the expression command
+// to make sure the resulting AST can be imported correctly.
+// CHECK: expr -- var
+// CHECK: (A::X) $0 = 0
+
+struct A {
+  // Declare the constructor, but don't define it to avoid emitting the
+  // definition in the debug info.
+  A();
+  using X = int;
+};
+
+A a;
+A::X var;

``````````

</details>


https://github.com/llvm/llvm-project/pull/102116