Fix crash in DefLocSaver (#7444)

* Add a failing test

    * thread #1, name = 'lsp_test_runner', stop reason = signal SIGSEGV: invalid address (fault address: 0x0)
      * frame #0: 0x0000000000e3d2c5 lsp_test_runner`absl::inlined_vector_internal::Storage<sorbet::core::SymbolRef, 1ul, std::__1::allocator<sorbet::core::SymbolRef>>::GetIsAllocated(this=0x0000000000000000) const at inlined_vector.h:353:40
        frame #1: 0x0000000000eabec9 lsp_test_runner`absl::InlinedVector<sorbet::core::SymbolRef, 1ul, std::__1::allocator<sorbet::core::SymbolRef>>::data(this=0x0000000000000000) const at inlined_vector.h:305:21
        frame #2: 0x0000000000eabb3a lsp_test_runner`absl::InlinedVector<sorbet::core::SymbolRef, 1ul, std::__1::allocator<sorbet::core::SymbolRef>>::operator=(this=0x00007fffffff6fe8, other=0x0000000000000000) at inlined_vector.h:465:40
        frame #3: 0x0000000000ea879f lsp_test_runner`sorbet::realmain::lsp::(anonymous namespace)::matchesQuery(ctx=Context @ 0x00007fffffff7100, lit=0x00000000035c0cc0, lspQuery=0x0000000002d0bfd0, symbolBeforeDealias=(_id = 24890)) at DefLocSaver.cc:121:24
        frame #4: 0x0000000000ea8357 lsp_test_runner`sorbet::realmain::lsp::DefLocSaver::postTransformConstantLit(this=0x00007fffffff86b8, ctx=Context @ 0x00007fffffff7148, tree=0x0000000002be4140) at DefLocSaver.cc:144:5
        frame #5: 0x0000000000e682da lsp_test_runner`decltype(self=0x00007fffffff86b8, args=0x00007fffffff7380, args=0x0000000002be4140) sorbet::ast::MapFunctions<(sorbet::ast::TreeMapKind)1>::CALL_MEMBER_impl_postTransformConstantLit<sorbet::realmain::lsp::DefLocSaver, true>::call<sorbet::core::Context&, sorbet::ast::ExpressionPtr&>(sorbet::realmain::lsp::DefLocSaver&, sorbet::core::Context&, sorbet::ast::ExpressionPtr&) at treemap.h:168:5
        frame #6: 0x0000000000e65ce8 lsp_test_runner`sorbet::ast::TreeMapper<sorbet::realmain::lsp::DefLocSaver, sorbet::core::Context, (sorbet::ast::TreeMapKind)1, (sorbet::ast::TreeMapDepthKind)0>::mapConstantLit(this=0x00007fffffff8648, v=0x0000000002be4140, ctx=Context @ 0x00007fffffff7380) at treemap.h:417:9
        frame #7: 0x0000000000e64515 lsp_test_runner`sorbet::ast::TreeMapper<sorbet::realmain::lsp::DefLocSaver, sorbet::core::Context, (sorbet::ast::TreeMapKind)1, (sorbet::ast::TreeMapDepthKind)0>::mapIt(this=0x00007fffffff8648, what=0x0000000002be4140, ctx=Context @ 0x00007fffffff7780) at treemap.h:569:28
        frame #8: 0x0000000000e649a0 lsp_test_runner`sorbet::ast::TreeMapper<sorbet::realmain::lsp::DefLocSaver, sorbet::core::Context, (sorbet::ast::TreeMapKind)1, (sorbet::ast::TreeMapDepthKind)0>::mapSend(this=0x00007fffffff8648, v=0x0000000002c9d308, ctx=Context @ 0x00007fffffff7bd0) at treemap.h:372:13
        frame #9: 0x0000000000e63c11 lsp_test_runner`sorbet::ast::TreeMapper<sorbet::realmain::lsp::DefLocSaver, sorbet::core::Context, (sorbet::ast::TreeMapKind)1, (sorbet::ast::TreeMapDepthKind)0>::mapIt(this=0x00007fffffff8648, what=0x0000000002c9d308, ctx=Context @ 0x00007fffffff7c50) at treemap.h:491:28
        frame #10: 0x0000000000e64dd4 lsp_test_runner`sorbet::ast::TreeMapper<sorbet::realmain::lsp::DefLocSaver, sorbet::core::Context, (sorbet::ast::TreeMapKind)1, (sorbet::ast::TreeMapDepthKind)0>::mapClassDef(this=0x00007fffffff8648, v=0x0000000002bc0fa0, ctx=Context @ 0x00007fffffff8070) at treemap.h:249:13
        frame #11: 0x0000000000e63c75 lsp_test_runner`sorbet::ast::TreeMapper<sorbet::realmain::lsp::DefLocSaver, sorbet::core::Context, (sorbet::ast::TreeMapKind)1, (sorbet::ast::TreeMapDepthKind)0>::mapIt(this=0x00007fffffff8648, what=0x0000000002bc0fa0, ctx=Context @ 0x00007fffffff80f0) at treemap.h:494:28
        frame #12: 0x0000000000e65e78 lsp_test_runner`sorbet::ast::TreeMapper<sorbet::realmain::lsp::DefLocSaver, sorbet::core::Context, (sorbet::ast::TreeMapKind)1, (sorbet::ast::TreeMapDepthKind)0>::mapInsSeq(this=0x00007fffffff8648, v=0x000000000246d3e0, ctx=Context @ 0x00007fffffff82f0) at treemap.h:438:13
        frame #13: 0x0000000000e645c6 lsp_test_runner`sorbet::ast::TreeMapper<sorbet::realmain::lsp::DefLocSaver, sorbet::core::Context, (sorbet::ast::TreeMapKind)1, (sorbet::ast::TreeMapDepthKind)0>::mapIt(this=0x00007fffffff8648, what=0x000000000246d3e0, ctx=Context @ 0x00007fffffff8638) at treemap.h:582:28
        frame #14: 0x0000000000e6397a lsp_test_runner`void sorbet::ast::TreeWalk::apply<sorbet::core::Context, sorbet::realmain::lsp::DefLocSaver>(ctx=Context @ 0x00007fffffff8680, func=0x00007fffffff86b8, to=0x000000000246d3e0) at treemap.h:622:20
        frame #15: 0x0000000000e52acc lsp_test_runner`sorbet::realmain::lsp::(anonymous namespace)::tryApplyDefLocSaver(gs=0x0000000002d0bf90, indexedCopies=size=1) at LSPTypechecker.cc:621:9
        frame #16: 0x0000000000e5235d lsp_test_runner`sorbet::realmain::lsp::LSPTypechecker::query(this=0x0000000002472050, q=0x00007fffffff8ca8, filesForQuery=size=1, workers=0x000000000246e9c0) const at LSPTypechecker.cc:643:5
        frame #17: 0x0000000000e53e1b lsp_test_runner`sorbet::realmain::lsp::LSPTypecheckerDelegate::query(this=0x0000000002bc27c0, q=0x00007fffffff8ca8, filesForQuery=size=1) const at LSPTypechecker.cc:770:24
        frame #18: 0x0000000000e42128 lsp_test_runner`sorbet::realmain::lsp::LSPQuery::byLoc(config=0x000000000246bcd8, typechecker=0x0000000002bc27c0, uri="file:///Users/jez/stripe/sorbet/test/testdata/lsp/hover_static_field_alias_to_nothing.rb", pos=0x0000000002bc0500, forMethod=TextDocumentHover, errorIfFileIsUntyped=true) at LSPQuery.cc:89:24
        frame #19: 0x0000000000f74ee0 lsp_test_runner`sorbet::realmain::lsp::HoverTask::runRequest(this=0x0000000002d373d0, typechecker=0x0000000002bc27c0) at hover.cc:44:19
        frame #20: 0x0000000000e3226c lsp_test_runner`sorbet::realmain::lsp::LSPRequestTask::run(this=0x0000000002d373d0, typechecker=0x0000000002bc27c0) at LSPTask.cc:222:21
        frame #21: 0x0000000000fbf3e4 lsp_test_runner`sorbet::realmain::lsp::(anonymous namespace)::TypecheckerTask::run(this=0x0000000002bc0028) at LSPTypecheckerCoordinator.cc:58:19
        frame #22: 0x0000000000fbda0e lsp_test_runner`sorbet::realmain::lsp::LSPTypecheckerCoordinator::asyncRunInternal(this=0x0000000002471db0, task=std::__1::shared_ptr<sorbet::core::lsp::Task>::element_type @ 0x0000000002bc0028 strong=2 weak=1) at LSPTypecheckerCoordinator.cc:129:15
        frame #23: 0x0000000000fbdae0 lsp_test_runner`sorbet::realmain::lsp::LSPTypecheckerCoordinator::syncRun(this=0x0000000002471db0, task=nullptr) at LSPTypecheckerCoordinator.cc:137:5
        frame #24: 0x0000000000fb34f8 lsp_test_runner`sorbet::realmain::lsp::LSPLoop::runTask(this=0x0000000002471d28, task=nullptr) at LSPLoop.cc:263:26
        frame #25: 0x0000000000fb2e38 lsp_test_runner`sorbet::realmain::lsp::LSPLoop::processRequests(this=0x0000000002471d28, messages=<unavailable>) at LSPLoop.cc:218:13
        frame #26: 0x0000000000fa3d6d lsp_test_runner`sorbet::realmain::lsp::SingleThreadedLSPWrapper::getLSPResponsesFor(this=0x000000000246ea10, messages=size=0) at wrapper.cc:68:14
        frame #27: 0x0000000000d2afd7 lsp_test_runner`sorbet::test::getLSPResponsesFor(wrapper=0x000000000246ea10, messages=size=0) at lsp.cc:490:27
        frame #28: 0x0000000000d2894e lsp_test_runner`sorbet::test::getLSPResponsesFor(wrapper=0x000000000246ea10, message=nullptr) at lsp.cc:530:12
        frame #29: 0x0000000000d664a3 lsp_test_runner`sorbet::test::HoverAssertion::check(this=0x0000000001eada28, sourceFileContents=0x00007fffffffc018, wrapper=0x000000000246ea10, nextId=0x00007fffffffbf24, errorPrefix="") at position_assertions.cc:1318:22
        frame #30: 0x0000000000d66224 lsp_test_runner`sorbet::test::HoverAssertion::checkAll(assertions=size=2, sourceFileContents=0x00007fffffffc018, wrapper=0x000000000246ea10, nextId=0x00007fffffffbf24, errorPrefix="") at position_assertions.cc:1280:30
        frame #31: 0x0000000000c29f46 lsp_test_runner`sorbet::test::DOCTEST_ANON_FUNC_58() at lsp_test_runner.cc:842:5
        frame #32: 0x0000000001de1180 lsp_test_runner`doctest::Context::run(this=0x00007fffffffcd58) at doctest.h:6930:21
        frame #33: 0x0000000000c2bcd0 lsp_test_runner`main(argc=2, argv=0x00007fffffffd258) at lsp_test_runner.cc:976:20
        frame #34: 0x00007ffff7c29d90 libc.so.6`__libc_start_call_main(main=(lsp_test_runner`main at lsp_test_runner.cc:959), argc=2, argv=0x00007fffffffd258) at libc_start_call_main.h:58:16
        frame #35: 0x00007ffff7c29e40 libc.so.6`__libc_start_main_impl(main=(lsp_test_runner`main at lsp_test_runner.cc:959), argc=2, argv=0x00007fffffffd258, init=<unavailable>, fini=<unavailable>, rtld_fini=<unavailable>, stack_end=0x00007fffffffd248) at libc-start.c:392:3
        frame #36: 0x0000000000c1ac85 lsp_test_runner`_start + 37

* Fix failing test

Author: jez

main/lsp/DefLocSaver.cc

@@ -117,7 +117,9 @@ void matchesQuery(core::Context ctx, ast::ConstantLit *lit, const core::lsp::Que
             }
 
             core::lsp::ConstantResponse::Scopes scopes;
-            if (symbol == core::Symbols::StubModule()) {
+            if (symbolBeforeDealias == core::Symbols::StubModule()) {
+                // If the symbol is an alias to a stub symbol, it actually resolved, and so it won't
+                // have resolutionScopes.
                 scopes = *lit->resolutionScopes;
             } else {
                 scopes = {symbol.owner(ctx)};

test/testdata/lsp/hover_static_field_alias_to_nothing.rb

@@ -0,0 +1,7 @@
+# typed: strict
+
+SomeConstant = DoesNotExist
+#              ^^^^^^^^^^^^ error: Unable to resolve constant `DoesNotExist`
+
+p(SomeConstant)
+#  ^ hover: This constant is not defined