Index: clang-tools-extra/trunk/clangd/refactor/tweaks/ExtractFunction.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/refactor/tweaks/ExtractFunction.cpp
+++ clang-tools-extra/trunk/clangd/refactor/tweaks/ExtractFunction.cpp
@@ -225,10 +225,24 @@
   return toHalfOpenFileRange(SM, LangOpts, EnclosingFunction->getSourceRange());
 }
 
+// returns true if Child can be a single RootStmt being extracted from
+// EnclosingFunc.
+bool validSingleChild(const Node *Child, const FunctionDecl *EnclosingFunc) {
+  // Don't extract expressions.
+  // FIXME: We should extract expressions that are "statements" i.e. not
+  // subexpressions
+  if (Child->ASTNode.get<Expr>())
+    return false;
+  // Extracting the body of EnclosingFunc would remove it's definition.
+  assert(EnclosingFunc->hasBody() &&
+         "We should always be extracting from a function body.");
+  if (Child->ASTNode.get<Stmt>() == EnclosingFunc->getBody())
+    return false;
+  return true;
+}
+
 // FIXME: Check we're not extracting from the initializer/condition of a control
 // flow structure.
-// FIXME: Check that we don't extract the compound statement of the
-// enclosingFunction.
 llvm::Optional<ExtractionZone> findExtractionZone(const Node *CommonAnc,
                                                   const SourceManager &SM,
                                                   const LangOptions &LangOpts) {
@@ -236,15 +250,14 @@
   ExtZone.Parent = getParentOfRootStmts(CommonAnc);
   if (!ExtZone.Parent || ExtZone.Parent->Children.empty())
     return llvm::None;
-  // Don't extract expressions.
-  // FIXME: We should extract expressions that are "statements" i.e. not
-  // subexpressions
-  if (ExtZone.Parent->Children.size() == 1 &&
-      ExtZone.getLastRootStmt()->ASTNode.get<Expr>())
-    return llvm::None;
   ExtZone.EnclosingFunction = findEnclosingFunction(ExtZone.Parent);
   if (!ExtZone.EnclosingFunction)
     return llvm::None;
+  // When there is a single RootStmt, we must check if it's valid for
+  // extraction.
+  if (ExtZone.Parent->Children.size() == 1 &&
+      !validSingleChild(ExtZone.getLastRootStmt(), ExtZone.EnclosingFunction))
+    return llvm::None;
   if (auto FuncRange =
           computeEnclosingFuncRange(ExtZone.EnclosingFunction, SM, LangOpts))
     ExtZone.EnclosingFuncRange = *FuncRange;
Index: clang-tools-extra/trunk/clangd/unittests/TweakTests.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/unittests/TweakTests.cpp
+++ clang-tools-extra/trunk/clangd/unittests/TweakTests.cpp
@@ -632,6 +632,13 @@
 
   // Shouldn't crash.
   EXPECT_EQ(apply("void f([[int a]]);"), "unavailable");
+  // Don't extract if we select the entire function body (CompoundStmt).
+  std::string CompoundFailInput = R"cpp(
+    void f() [[{
+      int a;
+    }]]
+  )cpp";
+  EXPECT_EQ(apply(CompoundFailInput), "unavailable");
 }
 
 TEST_F(ExtractFunctionTest, ControlFlow) {