Global code completion and architecture of clangd Ilya Biryukov - - PowerPoint PPT Presentation

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Global code completion and architecture of clangd Ilya Biryukov - - PowerPoint PPT Presentation

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Global code completion and architecture of clangd Ilya Biryukov Google EuroLLVM April 16, 2018 Overview 1. Language Server Protocol 2. Architecture of clangd 3. Code completion 4. Current state and future work Language Server Protocol

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Global code completion and architecture of clangd

Ilya Biryukov Google

EuroLLVM April 16, 2018

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Overview

1. Language Server Protocol 2. Architecture of clangd 3. Code completion 4. Current state and future work

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Language Server Protocol

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C++ Java C# Vim C++ Vim plugin Java Vim plugin C# Vim plugin Emacs C++ Emacs plugin Java Emacs plugin C# Emacs plugin Atom C++ Atom plugin Java Atom plugin C# Atom plugin Sublime Text C++ Sublime plugin Java Sublime plugin C# Sublime plugin

Editor integration problem

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Editor integration problem

vim Emacs irony-mode clang_complete vim-clang … rtags … libclang

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Language Server Protocol (LSP)

Editors (native or via plugins) vim Emacs Sublime Atom VSCode … Language Servers clangd(C++) cquery (C++) rlc (Rust) TypeScript Eclipse jdt.ls (Java) … LSP

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YouCompleteMe

Editors (via ycm plugins) vim Emacs Sublime Atom VSCode … Completers HTTP YCM Server C++ completer C# completer Java completer …

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clangd

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clangd

Language Server based on clang.

  • Developed as part of LLVM in clang-tools-extra
  • Supported features

○ Diagnostics ○ Code completion ○ Go to definition ○ Documentation ○ Local rename ○ Formatting ○ …

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Architecture of clangd

clangd clang Frontend AST Cache Index LSP features completion goto definition … signature help

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Index

  • Provides project-wide information
  • AST Decl → Index Symbol
  • Example:

namespace llvm { class StringRef { /* ... */ }; } int dropFirst(llvm::StringRef S, size_t N);

Name: StringRef Scope: llvm Kind: class ID: llvm::StringRef … Name: dropFirst Scope: <global-namespace> Kind: function ID: dropFirst(llvm::StringRef, size_t) …

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Index

Models of your program

AST

  • Single file
  • Up-to-date

Dynamic

  • Active files
  • ~1 minute old

Static

  • All files
  • ~1 day old
  • external?
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Code completion

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Clang completion of class members.

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Clang completion inside namespaces.

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Clang completion inside namespaces.

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Idea of global completion

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Idea of global completion

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Idea of global completion

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Global completion

  • Completion returns results

from all headers

○ adds #include if needed

  • General case is hard

std::vector<bool> vec_bool.flip(); // ok std::vector<int> vec_int; vec_int.flip(); // error

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Completion items: AST or Index?

namespace llvm { int getAsUnsignedInteger(const char *); class StringRef { const char *Ptr; public: StringRef substr(size_t N) { const char *NewPtr = Ptr + N; | } llvm::Optional llvm::DenseSet llvm::ArrayRef …

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Code completion flow

AST completions scopes index results clang Frontend PCH

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Index.fuzzyFind(/*Scopes*/ {"::", "std::"}, /*Query*/ "vec");

Scopes

void my_class::do_work() { vec| } #include "my_class.h" using namespace std;

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Ranking

  • Query match score
  • Symbol signals

○ Uses ○ Type information ○ Proximity

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Ranking example

Query: “uniq”

Match 0.9 0.9 0.5 0.5 Symbol unique unique_ptr make_unique MakeUnique Uses 45 1504 403 607 Uses 0.3 1.0 0.6 0.7 Total 0.27 0.9 0.30 0.35

× =

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Ranking example

Query: “uniq”

Symbol MakeUnique unique_ptr make_unique unique Total 0.35 0.9 0.30 0.27

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Current state and future work

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Current state

  • Basic LSP support

○ completion, diagnostics, fix-its, signature help, local rename, go to definition, formatting

  • Global completion (experimental)
  • Project-wide index (experimental)
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Embedding in a Web IDE

  • Used by internal Web IDE at Google
  • Runs in Cloud
  • Implementation challenges:

○ Virtual File System ○ Buildsystem integration ○ Tracing requests

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cquery

  • Language Server based on libclang
  • More features than clangd
  • Highly optimized in-memory index
  • Designed to run locally
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Future plans

  • More LSP features
  • clang-tidy
  • index-while-build
  • Better build system integration
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Thanks to all contributors!

  • Ben Jackson
  • Benjamin Kramer
  • Eric Liu
  • Haojian Wu
  • Krasimir Georgiev
  • Marc-André Laperle
  • Raoul Wols
  • Sam McCall
  • Simon Marchi
  • Stanislav Ionascu
  • William Enright
  • …
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  • Feedback welcome!

○ https://clang.llvm.org/extra/clangd.html

  • Contributions welcome!

○ https://reviews.llvm.org/source/CTE/browse/clang-tools-extra/trunk/clangd/ ○ https://clang.llvm.org/extra/clangd.html#getting-involved

  • Reach us at “cfe-dev”