[libclang] Fix crash in member access code completion with implicit base

[erikjv]

Summary

If there is an unresolved member access AST node, and the base is
implicit, do not access/use it for generating candidate overloads for
code completion results (because the base is a nullptr).

Fixes PR31093.

[arphaman]

It seems that unresolved member expressions have other lookup issues. For example, this will crash when code-completing as well:

struct Foo {
  void foo() const;
  static void foo(bool);
};

struct Bar: Foo {
  void foo(bool param) {
this->Foo::foo(/*CC CRASH*/  );// unresolved member expression with an explicit base
  }
};

Are we sure that a call to AddFunctionCandidates is the right way to gather the method overloads in this particular instance?

[bkramer]

Let's fix those crashes one at a time. This patch looks good, only minor comments below.

lib/Sema/SemaOverload.cpp

6311

This could use a comment explaining that this can happen if there's an error in the code, e.g. in code completion context.

6329

Same here.

[erikjv]

Landed as r298903.

lib/Sema/SemaCodeComplete.cpp

if (auto ULE = dyn_cast<UnresolvedLookupExpr>(NakedFn))
     AddOverloadedCallCandidates(ULE, Args, CandidateSet,
                                 /*PartialOverloading=*/true);
   else if (auto UME = dyn_cast<UnresolvedMemberExpr>(NakedFn)) {
     TemplateArgumentListInfo TemplateArgsBuffer, *TemplateArgs = nullptr;
     if (UME->hasExplicitTemplateArgs()) {
       UME->copyTemplateArgumentsInto(TemplateArgsBuffer);
       TemplateArgs = &TemplateArgsBuffer;
     }
-    SmallVector<Expr *, 12> ArgExprs(1, UME->getBase());
+    SmallVector<Expr *, 12> ArgExprs(
+        1, UME->isImplicitAccess() ? nullptr : UME->getBase());
     ArgExprs.append(Args.begin(), Args.end());
     UnresolvedSet<8> Decls;
     Decls.append(UME->decls_begin(), UME->decls_end());
     AddFunctionCandidates(Decls, ArgExprs, CandidateSet, TemplateArgs,
                           /*SuppressUsedConversions=*/false,
                           /*PartialOverloading=*/true);
   } else {
     FunctionDecl *FD = nullptr;

lib/Sema/SemaOverload.cpp

void Sema::AddFunctionCandidates(const UnresolvedSetImpl &Fns,
                                  ArrayRef<Expr *> Args,
                                  OverloadCandidateSet& CandidateSet,
                                  TemplateArgumentListInfo *ExplicitTemplateArgs,
                                  bool SuppressUserConversions,
                                  bool PartialOverloading) {
   for (UnresolvedSetIterator F = Fns.begin(), E = Fns.end(); F != E; ++F) {
     NamedDecl *D = F.getDecl()->getUnderlyingDecl();
     if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
-      if (isa<CXXMethodDecl>(FD) && !cast<CXXMethodDecl>(FD)->isStatic())
+      if (isa<CXXMethodDecl>(FD) && !cast<CXXMethodDecl>(FD)->isStatic()) {
+        QualType ObjectType;
+        Expr::Classification ObjectClassification;
+        if (Expr *E = Args[0]) {
+          ObjectType = E->getType();
+          ObjectClassification = E->Classify(Context);
+        }
         AddMethodCandidate(cast<CXXMethodDecl>(FD), F.getPair(),
-                           cast<CXXMethodDecl>(FD)->getParent(),
-                           Args[0]->getType(), Args[0]->Classify(Context),
-                           Args.slice(1), CandidateSet, SuppressUserConversions,
-                           PartialOverloading);
-      else
+                           cast<CXXMethodDecl>(FD)->getParent(), ObjectType,
+                           ObjectClassification, Args.slice(1), CandidateSet,
+                           SuppressUserConversions, PartialOverloading);
+      } else {
         AddOverloadCandidate(FD, F.getPair(), Args, CandidateSet,
                              SuppressUserConversions, PartialOverloading);
+      }
     } else {
       FunctionTemplateDecl *FunTmpl = cast<FunctionTemplateDecl>(D);
       if (isa<CXXMethodDecl>(FunTmpl->getTemplatedDecl()) &&
-          !cast<CXXMethodDecl>(FunTmpl->getTemplatedDecl())->isStatic())
+          !cast<CXXMethodDecl>(FunTmpl->getTemplatedDecl())->isStatic()) {
+        QualType ObjectType;
+        Expr::Classification ObjectClassification;
+        if (Expr *E = Args[0]) {
+          ObjectType = E->getType();
+          ObjectClassification = E->Classify(Context);
+        }
         AddMethodTemplateCandidate(
             FunTmpl, F.getPair(),
             cast<CXXRecordDecl>(FunTmpl->getDeclContext()),
-            ExplicitTemplateArgs, Args[0]->getType(),
-            Args[0]->Classify(Context), Args.slice(1), CandidateSet,
-            SuppressUserConversions, PartialOverloading);
-      else
+            ExplicitTemplateArgs, ObjectType, ObjectClassification,
+            Args.slice(1), CandidateSet, SuppressUserConversions,
+            PartialOverloading);
+      } else {
         AddTemplateOverloadCandidate(FunTmpl, F.getPair(),
                                      ExplicitTemplateArgs, Args,
                                      CandidateSet, SuppressUserConversions,
                                      PartialOverloading);
       }
     }
   }
+}
 
 /// AddMethodCandidate - Adds a named decl (which is some kind of
 /// method) as a method candidate to the given overload set.
 void Sema::AddMethodCandidate(DeclAccessPair FoundDecl,
                               QualType ObjectType,
                               Expr::Classification ObjectClassification,
                               ArrayRef<Expr *> Args,
                               OverloadCandidateSet& CandidateSet,

test/CodeCompletion/member-access.cpp

 struct Test1 {
   Base1 b;
 
   static void sfunc() {
     b. // expected-error {{invalid use of member 'b' in static member function}}
   }
 };
 
+struct Foo {
+  void foo() const;
+  static void foo(bool);
+};
+
+struct Bar {
+  void foo(bool param) {
+    Foo::foo(  );// unresolved member expression with an implicit base
+  }
+};
+
   // RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:29:6 %s -o - | FileCheck -check-prefix=CHECK-CC1 %s
   // CHECK-CC1: Base1 : Base1::
   // CHECK-CC1: member1 : [#int#][#Base1::#]member1
   // CHECK-CC1: member1 : [#int#][#Base2::#]member1
   // CHECK-CC1: member2 : [#float#][#Base1::#]member2
   // CHECK-CC1: member3
   // CHECK-CC1: member4
   // CHECK-CC1: memfun1 : [#void#][#Base3::#]memfun1(<#float#>)
   // CHECK-CC1: memfun1 : [#void#][#Base3::#]memfun1(<#double#>)[# const#]
   // CHECK-CC1: memfun1 (Hidden) : [#void#]Base2::memfun1(<#int#>)
   // CHECK-CC1: memfun2 : [#void#][#Base3::#]memfun2(<#int#>)
   // CHECK-CC1: memfun3 : [#int#]memfun3(<#int#>)
 
 // Make sure this doesn't crash
 // RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:36:7 %s -verify
+
+// Make sure this also doesn't crash
+// RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:47:14 %s