1 files changed, 268 insertions, 0 deletions
diff --git a/build/clang-plugin/mozsearch-plugin/from-clangd/HeuristicResolver.cpp b/build/clang-plugin/mozsearch-plugin/from-clangd/HeuristicResolver.cpp
new file mode 100644
index 0000000000..460b9be592
--- /dev/null
+++ b/build/clang-plugin/mozsearch-plugin/from-clangd/HeuristicResolver.cpp
@@ -0,0 +1,268 @@
+//===--- HeuristicResolver.cpp ---------------------------*- C++-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "HeuristicResolver.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/DeclTemplate.h"
+#include "clang/AST/ExprCXX.h"
+
+namespace clang {
+namespace clangd {
+
+// Convenience lambdas for use as the 'Filter' parameter of
+// HeuristicResolver::resolveDependentMember().
+const auto NoFilter = [](const NamedDecl *D) { return true; };
+const auto NonStaticFilter = [](const NamedDecl *D) {
+  return D->isCXXInstanceMember();
+};
+const auto StaticFilter = [](const NamedDecl *D) {
+  return !D->isCXXInstanceMember();
+};
+const auto ValueFilter = [](const NamedDecl *D) { return isa<ValueDecl>(D); };
+const auto TypeFilter = [](const NamedDecl *D) { return isa<TypeDecl>(D); };
+const auto TemplateFilter = [](const NamedDecl *D) {
+  return isa<TemplateDecl>(D);
+};
+
+// Helper function for HeuristicResolver::resolveDependentMember()
+// which takes a possibly-dependent type `T` and heuristically
+// resolves it to a CXXRecordDecl in which we can try name lookup.
+CXXRecordDecl *resolveTypeToRecordDecl(const Type *T) {
+  assert(T);
+
+  if (const auto *RT = T->getAs<RecordType>())
+    return dyn_cast<CXXRecordDecl>(RT->getDecl());
+
+  if (const auto *ICNT = T->getAs<InjectedClassNameType>())
+    T = ICNT->getInjectedSpecializationType().getTypePtrOrNull();
+  if (!T)
+    return nullptr;
+
+  const auto *TST = T->getAs<TemplateSpecializationType>();
+  if (!TST)
+    return nullptr;
+
+  const ClassTemplateDecl *TD = dyn_cast_or_null<ClassTemplateDecl>(
+      TST->getTemplateName().getAsTemplateDecl());
+  if (!TD)
+    return nullptr;
+
+  return TD->getTemplatedDecl();
+}
+
+const Type *HeuristicResolver::getPointeeType(const Type *T) const {
+  if (!T)
+    return nullptr;
+
+  if (T->isPointerType())
+    return T->castAs<PointerType>()->getPointeeType().getTypePtrOrNull();
+
+  // Try to handle smart pointer types.
+
+  // Look up operator-> in the primary template. If we find one, it's probably a
+  // smart pointer type.
+  auto ArrowOps = resolveDependentMember(
+      T, Ctx.DeclarationNames.getCXXOperatorName(OO_Arrow), NonStaticFilter);
+  if (ArrowOps.empty())
+    return nullptr;
+
+  // Getting the return type of the found operator-> method decl isn't useful,
+  // because we discarded template arguments to perform lookup in the primary
+  // template scope, so the return type would just have the form U* where U is a
+  // template parameter type.
+  // Instead, just handle the common case where the smart pointer type has the
+  // form of SmartPtr<X, ...>, and assume X is the pointee type.
+  auto *TST = T->getAs<TemplateSpecializationType>();
+  if (!TST)
+    return nullptr;
+  if (TST->template_arguments().size() == 0)
+    return nullptr;
+  const TemplateArgument &FirstArg = TST->template_arguments()[0];
+  if (FirstArg.getKind() != TemplateArgument::Type)
+    return nullptr;
+  return FirstArg.getAsType().getTypePtrOrNull();
+}
+
+std::vector<const NamedDecl *> HeuristicResolver::resolveMemberExpr(
+    const CXXDependentScopeMemberExpr *ME) const {
+  // If the expression has a qualifier, first try resolving the member
+  // inside the qualifier's type.
+  // Note that we cannot use a NonStaticFilter in either case, for a couple
+  // of reasons:
+  //   1. It's valid to access a static member using instance member syntax,
+  //      e.g. `instance.static_member`.
+  //   2. We can sometimes get a CXXDependentScopeMemberExpr for static
+  //      member syntax too, e.g. if `X::static_member` occurs inside
+  //      an instance method, it's represented as a CXXDependentScopeMemberExpr
+  //      with `this` as the base expression as `X` as the qualifier
+  //      (which could be valid if `X` names a base class after instantiation).
+  if (NestedNameSpecifier *NNS = ME->getQualifier()) {
+    if (const Type *QualifierType = resolveNestedNameSpecifierToType(NNS)) {
+      auto Decls =
+          resolveDependentMember(QualifierType, ME->getMember(), NoFilter);
+      if (!Decls.empty())
+        return Decls;
+    }
+  }
+
+  // If that didn't yield any results, try resolving the member inside
+  // the expression's base type.
+  const Type *BaseType = ME->getBaseType().getTypePtrOrNull();
+  if (ME->isArrow()) {
+    BaseType = getPointeeType(BaseType);
+  }
+  if (!BaseType)
+    return {};
+  if (const auto *BT = BaseType->getAs<BuiltinType>()) {
+    // If BaseType is the type of a dependent expression, it's just
+    // represented as BuiltinType::Dependent which gives us no information. We
+    // can get further by analyzing the dependent expression.
+    Expr *Base = ME->isImplicitAccess() ? nullptr : ME->getBase();
+    if (Base && BT->getKind() == BuiltinType::Dependent) {
+      BaseType = resolveExprToType(Base);
+    }
+  }
+  return resolveDependentMember(BaseType, ME->getMember(), NoFilter);
+}
+
+std::vector<const NamedDecl *> HeuristicResolver::resolveDeclRefExpr(
+    const DependentScopeDeclRefExpr *RE) const {
+  return resolveDependentMember(RE->getQualifier()->getAsType(),
+                                RE->getDeclName(), StaticFilter);
+}
+
+std::vector<const NamedDecl *>
+HeuristicResolver::resolveTypeOfCallExpr(const CallExpr *CE) const {
+  const auto *CalleeType = resolveExprToType(CE->getCallee());
+  if (!CalleeType)
+    return {};
+  if (const auto *FnTypePtr = CalleeType->getAs<PointerType>())
+    CalleeType = FnTypePtr->getPointeeType().getTypePtr();
+  if (const FunctionType *FnType = CalleeType->getAs<FunctionType>()) {
+    if (const auto *D =
+            resolveTypeToRecordDecl(FnType->getReturnType().getTypePtr())) {
+      return {D};
+    }
+  }
+  return {};
+}
+
+std::vector<const NamedDecl *>
+HeuristicResolver::resolveCalleeOfCallExpr(const CallExpr *CE) const {
+  if (const auto *ND = dyn_cast_or_null<NamedDecl>(CE->getCalleeDecl())) {
+    return {ND};
+  }
+
+  return resolveExprToDecls(CE->getCallee());
+}
+
+std::vector<const NamedDecl *> HeuristicResolver::resolveUsingValueDecl(
+    const UnresolvedUsingValueDecl *UUVD) const {
+  return resolveDependentMember(UUVD->getQualifier()->getAsType(),
+                                UUVD->getNameInfo().getName(), ValueFilter);
+}
+
+std::vector<const NamedDecl *> HeuristicResolver::resolveDependentNameType(
+    const DependentNameType *DNT) const {
+  return resolveDependentMember(
+      resolveNestedNameSpecifierToType(DNT->getQualifier()),
+      DNT->getIdentifier(), TypeFilter);
+}
+
+std::vector<const NamedDecl *>
+HeuristicResolver::resolveTemplateSpecializationType(
+    const DependentTemplateSpecializationType *DTST) const {
+  return resolveDependentMember(
+      resolveNestedNameSpecifierToType(DTST->getQualifier()),
+      DTST->getIdentifier(), TemplateFilter);
+}
+
+const Type *resolveDeclsToType(const std::vector<const NamedDecl *> &Decls) {
+  if (Decls.size() != 1) // Names an overload set -- just bail.
+    return nullptr;
+  if (const auto *TD = dyn_cast<TypeDecl>(Decls[0])) {
+    return TD->getTypeForDecl();
+  }
+  if (const auto *VD = dyn_cast<ValueDecl>(Decls[0])) {
+    return VD->getType().getTypePtrOrNull();
+  }
+  return nullptr;
+}
+
+std::vector<const NamedDecl *>
+HeuristicResolver::resolveExprToDecls(const Expr *E) const {
+  if (const auto *ME = dyn_cast<CXXDependentScopeMemberExpr>(E)) {
+    return resolveMemberExpr(ME);
+  }
+  if (const auto *RE = dyn_cast<DependentScopeDeclRefExpr>(E)) {
+    return resolveDeclRefExpr(RE);
+  }
+  if (const auto *OE = dyn_cast<OverloadExpr>(E)) {
+    return {OE->decls_begin(), OE->decls_end()};
+  }
+  if (const auto *CE = dyn_cast<CallExpr>(E)) {
+    return resolveTypeOfCallExpr(CE);
+  }
+  if (const auto *ME = dyn_cast<MemberExpr>(E))
+    return {ME->getMemberDecl()};
+
+  return {};
+}
+
+const Type *HeuristicResolver::resolveExprToType(const Expr *E) const {
+  std::vector<const NamedDecl *> Decls = resolveExprToDecls(E);
+  if (!Decls.empty())
+    return resolveDeclsToType(Decls);
+
+  return E->getType().getTypePtr();
+}
+
+const Type *HeuristicResolver::resolveNestedNameSpecifierToType(
+    const NestedNameSpecifier *NNS) const {
+  if (!NNS)
+    return nullptr;
+
+  // The purpose of this function is to handle the dependent (Kind ==
+  // Identifier) case, but we need to recurse on the prefix because
+  // that may be dependent as well, so for convenience handle
+  // the TypeSpec cases too.
+  switch (NNS->getKind()) {
+  case NestedNameSpecifier::TypeSpec:
+  case NestedNameSpecifier::TypeSpecWithTemplate:
+    return NNS->getAsType();
+  case NestedNameSpecifier::Identifier: {
+    return resolveDeclsToType(resolveDependentMember(
+        resolveNestedNameSpecifierToType(NNS->getPrefix()),
+        NNS->getAsIdentifier(), TypeFilter));
+  }
+  default:
+    break;
+  }
+  return nullptr;
+}
+
+std::vector<const NamedDecl *> HeuristicResolver::resolveDependentMember(
+    const Type *T, DeclarationName Name,
+    llvm::function_ref<bool(const NamedDecl *ND)> Filter) const {
+  if (!T)
+    return {};
+  if (auto *ET = T->getAs<EnumType>()) {
+    auto Result = ET->getDecl()->lookup(Name);
+    return {Result.begin(), Result.end()};
+  }
+  if (auto *RD = resolveTypeToRecordDecl(T)) {
+    if (!RD->hasDefinition())
+      return {};
+    RD = RD->getDefinition();
+    return RD->lookupDependentName(Name, Filter);
+  }
+  return {};
+}
+
+} // namespace clangd
+} // namespace clang