From 5c19a48b952f07f39e00e8487aa52227a9924c28 Mon Sep 17 00:00:00 2001
From: Itamar <itamar8910@gmail.com>
Date: Fri, 7 May 2021 15:20:05 +0300
Subject: [PATCH] CppLanguageServer: Cache declarations from headers in every
 document

Previously, to get the globally available declarations in a document
(including declarations from headers), we would have to recursively
walk the #include tree and get the declarations of each included
document.

To improve upon this, we now store a HashTable of globally available
declaration from included header files in each document, and populate
it when we first process the document.

Before this, invoking simple autocomplete actions in code documents
that had a very large #include tree (e.g when <LibGUI/Widget.h> was
included) hang the CppLanguageServer process and used 100% CPU until
the process ran out of memory.

Now, the autocomplete request in that situation returns immediately :^)
---
 .../Cpp/ParserAutoComplete.cpp                | 28 +++++++++----------
 .../LanguageServers/Cpp/ParserAutoComplete.h  |  5 +++-
 2 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.cpp b/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.cpp
index 2a8b598092..e3c195a4db 100644
--- a/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.cpp
+++ b/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.cpp
@@ -44,12 +44,7 @@ OwnPtr<ParserAutoComplete::DocumentData> ParserAutoComplete::create_document_dat
     auto document = filedb().get_or_create_from_filesystem(file);
     if (!document)
         return {};
-    auto content = document->text();
-    auto document_data = create_document_data(document->text(), file);
-
-    update_declared_symbols(*document_data);
-
-    return document_data;
+    return create_document_data(document->text(), file);
 }
 
 void ParserAutoComplete::set_document_data(const String& file, OwnPtr<DocumentData>&& data)
@@ -260,13 +255,8 @@ Vector<ParserAutoComplete::PropertyInfo> ParserAutoComplete::properties_of_type(
 NonnullRefPtrVector<Declaration> ParserAutoComplete::get_global_declarations_including_headers(const DocumentData& document) const
 {
     NonnullRefPtrVector<Declaration> declarations;
-    for (auto& include : document.preprocessor().included_paths()) {
-        document_path_from_include_path(include);
-        auto included_document = get_document_data(document_path_from_include_path(include));
-        if (!included_document)
-            continue;
-        declarations.append(get_global_declarations_including_headers(*included_document));
-    }
+    for (auto& decl : document.m_declarations_from_headers)
+        declarations.append(*decl);
 
     declarations.append(get_global_declarations(*document.parser().root_node()));
 
@@ -434,8 +424,16 @@ RefPtr<Declaration> ParserAutoComplete::find_declaration_of(const DocumentData&
     return {};
 }
 
-void ParserAutoComplete::update_declared_symbols(const DocumentData& document)
+void ParserAutoComplete::update_declared_symbols(DocumentData& document)
 {
+    for (auto& include : document.preprocessor().included_paths()) {
+        auto included_document = get_or_create_document_data(document_path_from_include_path(include));
+        if (!included_document)
+            continue;
+        for (auto&& decl : get_global_declarations_including_headers(*included_document))
+            document.m_declarations_from_headers.set(move(decl));
+    }
+
     Vector<GUI::AutocompleteProvider::Declaration> declarations;
 
     for (auto& decl : get_global_declarations(*document.parser().root_node())) {
@@ -494,6 +492,8 @@ OwnPtr<ParserAutoComplete::DocumentData> ParserAutoComplete::create_document_dat
     if constexpr (CPP_LANGUAGE_SERVER_DEBUG)
         root->dump(0);
 
+    update_declared_symbols(*document_data);
+
     return document_data;
 }
 
diff --git a/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.h b/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.h
index 5d8c4487db..39db9c8656 100644
--- a/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.h
+++ b/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.h
@@ -59,6 +59,9 @@ private:
         String m_text;
         OwnPtr<Preprocessor> m_preprocessor;
         OwnPtr<Parser> m_parser;
+
+        // FIXME: This HashTable must be re-computed if a declaration from a header file is modified
+        HashTable<NonnullRefPtr<Declaration>> m_declarations_from_headers;
     };
 
     Vector<GUI::AutocompleteProvider::Entry> autocomplete_property(const DocumentData&, const MemberExpression&, const String partial_text) const;
@@ -85,7 +88,7 @@ private:
 
     OwnPtr<DocumentData> create_document_data_for(const String& file);
     String document_path_from_include_path(const StringView& include_path) const;
-    void update_declared_symbols(const DocumentData&);
+    void update_declared_symbols(DocumentData&);
     GUI::AutocompleteProvider::DeclarationType type_of_declaration(const Declaration&);
     String scope_of_declaration(const Declaration&);
     Optional<GUI::AutocompleteProvider::ProjectLocation> find_preprocessor_definition(const DocumentData&, const GUI::TextPosition&);