[clang-tools-extra] [clangd] Handle lambda scopes inside Node::getDeclContext() (PR #76329)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 created https://github.com/llvm/llvm-project/pull/76329

We used to consider the `DeclContext` for selection nodes inside a lambda as the enclosing scope of the lambda expression, rather than the lambda itself.

For example,

```cpp
void foo();
auto lambda = [] {
  return ^foo();
};
```

where `N` is the selection node for the expression `foo()`, `N.getDeclContext()` returns the `TranslationUnitDecl` previously, which IMO is wrong, since the `RecordDecl` of the lambda is closer.

Seemingly, this affects nothing currently.

>From c0b04507075b39e494d3e6fa39168bc47b92f338 Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Sun, 24 Dec 2023 18:08:30 +0800
Subject: [PATCH] [clangd] Handle lambda scopes inside Node::getDeclContext()

We used to consider the DeclContext for selection nodes inside
a lambda as the scope of the lambda expression locates in.

For example,

```cpp
void foo();
auto lambda = [] {
  return ^foo();
};
```

where N is the selection node for the expression `foo()`,
`N.getDeclContext()` returns the TranslationUnitDecl previously,
which IMO is wrong, since the RecordDecl of the lambda is closer.
---
 clang-tools-extra/clangd/Selection.cpp              |  3 +++
 .../clangd/unittests/SelectionTests.cpp             | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/clang-tools-extra/clangd/Selection.cpp b/clang-tools-extra/clangd/Selection.cpp
index 8c6d5750ecefdb..a7413485b04ac3 100644
--- a/clang-tools-extra/clangd/Selection.cpp
+++ b/clang-tools-extra/clangd/Selection.cpp
@@ -1113,6 +1113,9 @@ const DeclContext &SelectionTree::Node::getDeclContext() const {
           return *DC;
       return *Current->getLexicalDeclContext();
     }
+    if (auto *LE = CurrentNode->ASTNode.get<LambdaExpr>())
+      if (CurrentNode != this)
+        return *LE->getLambdaClass();
   }
   llvm_unreachable("A tree must always be rooted at TranslationUnitDecl.");
 }
diff --git a/clang-tools-extra/clangd/unittests/SelectionTests.cpp b/clang-tools-extra/clangd/unittests/SelectionTests.cpp
index 4c019a1524f3c3..cdb50dfc1c3095 100644
--- a/clang-tools-extra/clangd/unittests/SelectionTests.cpp
+++ b/clang-tools-extra/clangd/unittests/SelectionTests.cpp
@@ -880,6 +880,19 @@ TEST(SelectionTest, DeclContextIsLexical) {
   }
 }
 
+TEST(SelectionTest, DeclContextLambda) {
+  llvm::Annotations Test(R"cpp(
+    void foo();
+    auto lambda = [] {
+      return $1^foo();
+    };
+  )cpp");
+  auto AST = TestTU::withCode(Test.code()).build();
+  auto ST = SelectionTree::createRight(AST.getASTContext(), AST.getTokens(),
+                                       Test.point("1"), Test.point("1"));
+  EXPECT_FALSE(ST.commonAncestor()->getDeclContext().isTranslationUnit());
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang