[clang] [clang][ExtractAPI] fix a couple crashes when used via libclang (PR #132297)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: QuietMisdreavus (QuietMisdreavus)

<details>
<summary>Changes</summary>

This PR fixes two crashes in ExtractAPI that occur when decls are requested via libclang:

- A null-dereference would sometimes happen in `DeclarationFragmentsBuilder::getFragmentsForClassTemplateSpecialization` when the template being processed was loaded indirectly via a typedef, with parameters filled in. The first commit loads the template parameter locations ahead of time to perform a null check before dereferencing.
- An assertion (or another null-dereference) was happening in `CXXRecordDecl::bases` when processing a forward-declaration (i.e. a record without a definition). The second commit guards the use of `bases` in `ExtractAPIVisitorBase::getBases` by first checking that the decl in question has a complete definition.

The added test `extract-api-cursor-cpp` adds tests for these two scenarios to protect against the crash in the future.

Fixes rdar://140592475, fixes rdar://123430367

---
Full diff: https://github.com/llvm/llvm-project/pull/132297.diff


3 Files Affected:

- (modified) clang/include/clang/ExtractAPI/ExtractAPIVisitor.h (+22-20) 
- (modified) clang/lib/ExtractAPI/DeclarationFragments.cpp (+5-1) 
- (added) clang/test/Index/extract-api-cursor-cpp.cpp (+33) 


``````````diff
diff --git a/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h b/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h
index e60440e14a9fe..13e51413017d5 100644
--- a/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h
+++ b/clang/include/clang/ExtractAPI/ExtractAPIVisitor.h
@@ -175,28 +175,30 @@ class ExtractAPIVisitorBase : public RecursiveASTVisitor<Derived> {
   SmallVector<SymbolReference> getBases(const CXXRecordDecl *Decl) {
     // FIXME: store AccessSpecifier given by inheritance
     SmallVector<SymbolReference> Bases;
-    for (const auto &BaseSpecifier : Decl->bases()) {
-      // skip classes not inherited as public
-      if (BaseSpecifier.getAccessSpecifier() != AccessSpecifier::AS_public)
-        continue;
-      if (auto *BaseDecl = BaseSpecifier.getType()->getAsTagDecl()) {
-        Bases.emplace_back(createSymbolReferenceForDecl(*BaseDecl));
-      } else {
-        SymbolReference BaseClass;
-        BaseClass.Name = API.copyString(BaseSpecifier.getType().getAsString(
-            Decl->getASTContext().getPrintingPolicy()));
-
-        if (BaseSpecifier.getType().getTypePtr()->isTemplateTypeParmType()) {
-          if (auto *TTPTD = BaseSpecifier.getType()
-                                ->getAs<TemplateTypeParmType>()
-                                ->getDecl()) {
-            SmallString<128> USR;
-            index::generateUSRForDecl(TTPTD, USR);
-            BaseClass.USR = API.copyString(USR);
-            BaseClass.Source = API.copyString(getOwningModuleName(*TTPTD));
+    if (Decl->isCompleteDefinition()) {
+      for (const auto &BaseSpecifier : Decl->bases()) {
+        // skip classes not inherited as public
+        if (BaseSpecifier.getAccessSpecifier() != AccessSpecifier::AS_public)
+          continue;
+        if (auto *BaseDecl = BaseSpecifier.getType()->getAsTagDecl()) {
+          Bases.emplace_back(createSymbolReferenceForDecl(*BaseDecl));
+        } else {
+          SymbolReference BaseClass;
+          BaseClass.Name = API.copyString(BaseSpecifier.getType().getAsString(
+              Decl->getASTContext().getPrintingPolicy()));
+
+          if (BaseSpecifier.getType().getTypePtr()->isTemplateTypeParmType()) {
+            if (auto *TTPTD = BaseSpecifier.getType()
+                                  ->getAs<TemplateTypeParmType>()
+                                  ->getDecl()) {
+              SmallString<128> USR;
+              index::generateUSRForDecl(TTPTD, USR);
+              BaseClass.USR = API.copyString(USR);
+              BaseClass.Source = API.copyString(getOwningModuleName(*TTPTD));
+            }
           }
+          Bases.emplace_back(BaseClass);
         }
-        Bases.emplace_back(BaseClass);
       }
     }
     return Bases;
diff --git a/clang/lib/ExtractAPI/DeclarationFragments.cpp b/clang/lib/ExtractAPI/DeclarationFragments.cpp
index 66c03863293c2..480e33f607bb0 100644
--- a/clang/lib/ExtractAPI/DeclarationFragments.cpp
+++ b/clang/lib/ExtractAPI/DeclarationFragments.cpp
@@ -1225,6 +1225,10 @@ DeclarationFragments
 DeclarationFragmentsBuilder::getFragmentsForClassTemplateSpecialization(
     const ClassTemplateSpecializationDecl *Decl) {
   DeclarationFragments Fragments;
+  std::optional<ArrayRef<TemplateArgumentLoc>> TemplateArgumentLocs = {};
+  if (auto *TemplateArgs = Decl->getTemplateArgsAsWritten()) {
+    TemplateArgumentLocs = TemplateArgs->arguments();
+  }
   return Fragments
       .append("template", DeclarationFragments::FragmentKind::Keyword)
       .appendSpace()
@@ -1237,7 +1241,7 @@ DeclarationFragmentsBuilder::getFragmentsForClassTemplateSpecialization(
       .append("<", DeclarationFragments::FragmentKind::Text)
       .append(getFragmentsForTemplateArguments(
           Decl->getTemplateArgs().asArray(), Decl->getASTContext(),
-          Decl->getTemplateArgsAsWritten()->arguments()))
+          TemplateArgumentLocs))
       .append(">", DeclarationFragments::FragmentKind::Text)
       .appendSemicolon();
 }
diff --git a/clang/test/Index/extract-api-cursor-cpp.cpp b/clang/test/Index/extract-api-cursor-cpp.cpp
new file mode 100644
index 0000000000000..c3219ddece73a
--- /dev/null
+++ b/clang/test/Index/extract-api-cursor-cpp.cpp
@@ -0,0 +1,33 @@
+// Test is line- and column-sensitive. Run lines are below
+
+template <typename T>
+class basic_vector {
+public:
+    T x;
+    T y;
+};
+
+using my_vec = basic_vector<int>;
+
+class MyClass {
+    my_vec myVec;
+};
+
+struct OuterStruct {
+    struct InnerStruct;
+    int outer_field;
+};
+
+// RUN: c-index-test -single-symbol-sgf-at=%s:13:13 local %s | FileCheck --check-prefix=CHECK-MYVEC %s
+// CHECK-MYVEC: "parentContexts":[{"kind":"c++.class","name":"MyClass","usr":"c:@S at MyClass"},{"kind":"c++.property","name":"myVec","usr":"c:@S at MyClass@FI at myVec"}]
+// CHECK-MYVEC: "identifier":{"interfaceLanguage":"c++","precise":"c:@S at MyClass@FI at myVec"}
+// CHECK-MYVEC: "kind":{"displayName":"Instance Property","identifier":"c++.property"}
+// CHECK-MYVEC: "title":"myVec"
+// CHECK-MYVEC: "pathComponents":["MyClass","myVec"]
+
+// RUN: c-index-test -single-symbol-sgf-at=%s:17:17 local %s | FileCheck --check-prefix=CHECK-INNER %s
+// CHECK-INNER: "parentContexts":[{"kind":"c++.struct","name":"OuterStruct","usr":"c:@S at OuterStruct"},{"kind":"c++.struct","name":"InnerStruct","usr":"c:@S at OuterStruct@S at InnerStruct"}]
+// CHECK-INNER: "identifier":{"interfaceLanguage":"c++","precise":"c:@S at OuterStruct@S at InnerStruct"}
+// CHECK-INNER: "kind":{"displayName":"Structure","identifier":"c++.struct"}
+// CHECK-INNER: "title":"InnerStruct"
+// CHECK-INNER: "pathComponents":["OuterStruct","InnerStruct"]

``````````

</details>


https://github.com/llvm/llvm-project/pull/132297