YouCompleteMe: a code-completion engine for Vim =============================================== YouCompleteMe is a fast, as-you-type, fuzzy-search code completion engine for [Vim][]. It has two completion engines: an identifier-based engine that works with every programming language and a semantic, [Clang][]-based engine that provides semantic code completion for C/C++/Objective-C/Objective-C++ (from now on referred to as "the C-family languages"). ![YouCompleteMe GIF demo](http://i.imgur.com/0OP4ood.gif) Here's an explanation of what happens in the short GIF demo above. First, realize that **no keyboard shortcuts had to be pressed** to get the list of completion candidates at any point in the demo. The user just types and the suggestions pop up by themselves. If the user doesn't find the completion suggestions relevant and/or just wants to type, he can do so; the completion engine will not interfere. When the user sees a useful completion string being offered, he presses the TAB key to accept it. This inserts the completion string. Repeated presses of the TAB key cycle through the offered completions. If the offered completions are not relevant enough, the user can continue typing to further filter out unwanted completions. A critical thing to notice is that the completion **filtering is NOT based on the input being a string prefix of the completion** (but that works too). The input needs to be a _[subsequence][] match_ of a completion. This is a fancy way of saying that any input characters need to be present in a completion string in the order in which they appear in the input. So `abc` is a subsequence of `xaybgc`, but not of `xbyxaxxc`. After the filter, a complicated sorting system ranks the completion strings so that the most relevant ones rise to the top of the menu (so you usually need to press TAB just once). **All of the above works with any programming language** because of the identifier-based completion engine. It collects all of the identifiers in the current file and other files you visit and searches them when you type (identifiers are put into per-filetype groups). The demo also shows the semantic engine in use. The current semantic engine supports only C-family languages. When the user presses `.`, `->` or `::` while typing in insert mode, the semantic engine is triggered (it can also be triggered with a keyboard shortcut; see the rest of the docs). The last thing that you can see in the demo is YCM's integration with [Syntastic][] (the little red X that shows up in the left gutter) if you are editing a file with semantic engine support. As Clang compiles your file and detects warnings or errors, they will be piped to Syntastic for display. You don't need to save your file or press any keyboard shortcut to trigger this, it "just happens" in the background. In essence, YCM obsoletes the following Vim plugins because it has all of their features plus extra: - clang_complete - AutoComplPop - Supertab - neocomplcache Mac OS X super-quick installation --------------------------------- Please refer to the full Installation Guide below; the following commands are provided on a best-effort basis and may not work for you. Install the latest version of [MacVim][]. Yes, MacVim. And yes, the _latest_. Install YouCompleteMe with [Vundle][]. Install CMake. Preferably with [Homebrew][brew], but here's the [stand-alone CMake installer][cmake-download]. _If_ you care about semantic completion for C-family languages, type in the following commands in the console. If you don't, **skip this step**. cd ~ mkdir ycm_temp cd ycm_temp curl -O http://llvm.org/releases/3.2/clang+llvm-3.2-x86_64-apple-darwin11.tar.gz tar -zxvf clang+llvm-3.2-x86_64-apple-darwin11.tar.gz cp clang+llvm-3.2-x86_64-apple-darwin11/lib/libclang.dylib ~/.vim/bundle/YouCompleteMe/python Compiling YCM **with** semantic support for C-family languages (previous step required): cd ~ makedir ycm_build cd ycm_build cmake -G "Unix Makefiles" -DPATH_TO_LLVM_ROOT=~/ycm_temp/clang+llvm-3.2-x86_64-apple-darwin11 . ~/.vim/bundle/YouCompleteMe/cpp make ycm_core Compiling YCM **without** semantic support for C-family languages: cd ~ makedir ycm_build cd ycm_build cmake -G "Unix Makefiles" . ~/.vim/bundle/YouCompleteMe/cpp make ycm_core That's it. You're done. Refer to the User Guide section on how to use YCM. Don't forget that if you want the C-family semantic completion engine to work, you will need to provide the compilation flags for your project to YCM. It's all in the User Guide. YCM comes with sane defaults for its options, but you still may want to take a look at what's available for configuration. There are a few interesting options that are conservatively turned off by default that you may want to turn on. Ubuntu Linux x64 super-quick installation ----------------------------------------- Please refer to the full Installation Guide below; the following commands are provided on a best-effort basis and may not work for you. Make sure you have Vim 7.3.584 with python2 support. At the time of writing, the version of Vim shipping with Ubuntu is too old. You may need to compile Vim from source. Install YouCompleteMe with [Vundle][]. Install CMake. `sudo apt-get instal cmake` _If_ you care about semantic completion for C-family languages, type in the following commands in the console. If you don't, **skip this step**. cd ~ mkdir ycm_temp cd ycm_temp curl -O http://llvm.org/releases/3.2/clang+llvm-3.2-x86_64-linux-ubuntu-12.04.tar.gz tar -zxvf clang+llvm-3.2-x86_64-linux-ubuntu-12.04.tar.gz cp clang+llvm-3.2-x86_64-linux-ubuntu-12.04/lib/libclang.so ~/.vim/bundle/YouCompleteMe/python Compiling YCM **with** semantic support for C-family languages (previous step required): cd ~ mkdir ycm_build cd ycm_build cmake -G "Unix Makefiles" -DPATH_TO_LLVM_ROOT=~/ycm_temp/clang+llvm-3.2-x86_64-linux-ubuntu-12.04 . ~/.vim/bundle/YouCompleteMe/cpp make ycm_core Compiling YCM **without** semantic support for C-family languages: cd ~ mkdir ycm_build cd ycm_build cmake -G "Unix Makefiles" . ~/.vim/bundle/YouCompleteMe/cpp make ycm_core That's it. You're done. Refer to the User Guide section on how to use YCM. Don't forget that if you want the C-family semantic completion engine to work, you will need to provide the compilation flags for your project to YCM. It's all in the User Guide. YCM comes with sane defaults for its options, but you still may want to take a look at what's available for configuration. There are a few interesting options that are conservatively turned off by default that you may want to turn on. Full Installation Guide ----------------------- These are the steps necessary to get YCM working on a Unix OS like Linux or Mac OS X. My apologies to Windows users, but I don't have a guide for them. The code is platform agnostic, so if everything is configured correctly, YCM _should_ work on Windows without issues (but as of writing, it's untested on that platform). **Please follow the instructions carefully. Read EVERY WORD.** 1. **Ensure that your version of Vim is _at least_ 7.3.584 _and_ that it has support for python2 scripting**. Inside Vim, type `:version`. Look at the first two to three lines of output; it should say `Vi IMproved 7.3` and then below that, `Included patches: 1-X`, where X will be some number. That number needs to be 584 or higher. After you have made sure that you have Vim 7.3.584+, type the following in Vim: `:has('python')`. The output should be 1. If it's 0, then get a version of Vim with Python support. 2. **Install YCM** with [Vundle][] (or [Pathogen][], but Vundle is a better idea). With Vundle, this would mean adding a `Bundle 'Valloric/YouCompleteMe'` line to your [vimrc][]. 3. [Complete this step ONLY if you care about semantic completion support for C-family languages. Otherwise it's not neccessary.] **Download the latest version of `libclang`**. Clang is an open-source compiler that can compile C/C++/Objective-C/Objective-C++. The `libclang` library it provides is used to power the YCM semantic completion engine for those languages. YCM needs libclang version 3.2 or higher. You can use the system libclang _only if you are sure it is version 3.2 or higher_, otherwise don't. Even if it is, I recommend using the [official binaries from llvm.org][clang-download] if at all possible. Make sure you download the correct archive file for your OS. 4. **Compile the `ycm_core` plugin plugin** (ha!) that YCM needs. This is the C++ engine that YCM uses to get fast completions. You will need to have `cmake` installed in order to generate the required makefiles. Linux users can install cmake with their package manager (`sudo apt-get install cmake` for Ubuntu) whereas other users can [download and install][cmake-download] cmake from its project site. Mac users can also get it through [Homebrew][brew] with `brew install cmake`. Here we'll assume you installed YCM with Vundle. That means that the top-level YCM directory is in `~/.vim/bundle/YouCompleteMe`. We'll create a new folder where build files will be placed. Run the following: cd ~ mkdir ycm_build cd ycm_build Now we need to generate the makefiles. If you DON'T care about semantic support for C-family languages, run the following command in the `ycm_build` directory: `cmake -G "Unix Makefiles" . ~/.vim/bundle/YouCompleteMe/cpp` If you DO care about semantic support for C-family languages, then your `cmake` call will be a bit more complicated. We'll assume you downloaded a binary distribution of LLVM+Clang from llvm.org in step 3 and that you extracted the archive file to folder `~/ycm_temp/llvm_root_dir` (with `bin`, `lib`, `include` etc. folders right inside that folder). With that in mind, run the following command in the `ycm_build` directory: `cmake -G "Unix Makefiles" -DPATH_TO_LLVM_ROOT=~/ycm_temp/llvm_root_dir . ~/.vim/bundle/YouCompleteMe/cpp` Now that makefiles have been generated, simply run `make ycm_core`. For those who want to use the system version of libclang, you would pass `-DUSE_SYSTEM_LIBCLANG=ON` to cmake _instead of_ the `-DPATH_TO_LLVM_ROOT=...` flag. You could also force the use of a custom libclang library with `-DEXTERNAL_LIBCLANG_PATH=/path/to/libclang.so` flag (the library would end with `.dylib` on a Mac). Again, this flag would be used _instead of_ the other flags. 5. [Complete this step ONLY if you care about semantic completion support for C-family languages. Otherwise it's not neccessary.] **Copy the libclang library file into the `YouCompleteMe/python` folder.** The library file is `libclang.so` on Linux and `libclang.dylib` on Mac. We'll assume you downloaded a binary distribution of LLVM+Clang from llvm.org in step 3 and that you extracted the archive file to folder `~/ycm_temp/llvm_root_dir` (with `bin`, `lib`, `include` etc. folders right inside that folder). We'll also assume you installed YCM with Vundle. That means that the top-level YCM directory is in `~/.vim/bundle/YouCompleteMe`. On Linux, run: `cp ~/ycm_temp/llvm_root_dir/lib/libclang.so ~/.vim/bundle/YouCompleteMe/python` On Mac, run: `cp ~/ycm_temp/llvm_root_dir/lib/libclang.dylib ~/.vim/bundle/YouCompleteMe/python` **DO NOT FORGET THIS STEP**. If you forget to copy over `libclang.so` version 3.2 into the `YouCompleteMe/python` folder then YCM _will not work_ if you selected C-family support during YCM compilation. That's it. You're done. Refer to the User Guide section on how to use YCM. Don't forget that if you want the C-family semantic completion engine to work, you will need to provide the compilation flags for your project to YCM. It's all in the User Guide. YCM comes with sane defaults for its options, but you still may want to take a look at what's available for configuration. There are a few interesting options that are conservatively turned off by default that you may want to turn on. User Guide ---------- ### General Usage - If the offered completions are too broad, keep typing characters; YCM will continue refining the offered completions based on your input. - Use the TAB key to accept a completion and continue pressing TAB to cycle through the completions. Use Shift-TAB to cycle backwards. Note that if you're using console Vim (that is, not Gvim or MacVim) then it's likely that the Shift-TAB binding will not work because the console will not pass it to Vim. You can remap the keys; see the options section below. ### Completion string ranking The subsequence filter removes any completions that do not match the input, but then the sorting system kicks in. It's actually very complicated and uses lots of factors, but suffice it to say that "word boundary" (WB) subsequence character matches are "worth" more than non-WB matches. In effect, this means given an input of "gua", the completion "getUserAccount" would be ranked higher in the list than the "Fooguxa" completion (both of which are subsequence matches). A word-boundary character are all capital characters, characters preceded by an underscore and the first letter character in the completion string. ### Semantic Completion Engine Usage - You can use Ctrl+Space to trigger the completion suggestions anywhere, even without a string prefix. This is useful to see which top-level functions are available for use. - You _really_ also want to install the latest version of the [Syntastic][] Vim plugin. It has support for YCM and together they will provide you with compile errors/warnings practically instantly and without saving the file. YCM looks for a `.ycm_extra_conf.py` file in the directory of the opened file or in any directory above it in the hierarchy (recursively); when the file is found, it is loaded (only once!) as a Python module. YCM calls a `FlagsForFile` method in that module which should provide it with the information necessary to compile the current file. (You can also provide a path to a global `.ycm_extra_conf.py` file and override this searching behavior. See the Options section for more details.) This system was designed this way so that the user can perform any arbitrary sequence of operations to produce a list of compilation flags YCM should hand to Clang. [See YCM's own `.ycm_extra_conf.py`][flags_example] for details on how this works. You should be able to use it as a starting point. Hint: just replace the strings in the `flags` variable with compilation flags necessary for your project. That should be enough for 99% of projects. Yes, [Clang's `CompilationDatabase` system][compdb] is also supported. Again, see the above linked example file. If Clang encounters errors when compiling the header files that your file includes, then it's probably going to take a long time to get completions. When the completion menu finally appears, it's going to have a large number of unrelated completion strings (type/function names that are not actually members). This is because Clang fails to build a precompiled preamble for your file if there are any errors in the included headers and that preamble is key to getting fast completions. Call the `:YcmDiags` command to see if any errors or warnings were detected in your file. Even better, use Syntastic. ### Syntastic integration YCM has explicit support for [Syntastic][] (and vice-versa) if you compiled YCM with Clang support; this means that any diagnostics (errors or warnings) that Clang encounters while compiling your file will be fed back to Syntastic for display. YCM will recompile your file in the background `updatetime` (see `:h updatetime` in Vim) milliseconds after you stop typing (to be specific, on `CursorHold` and `CursorHoldI` Vim events). YCM will change your `updatetime` value to be `2000` milliseconds (there's an option to tell it not to do this if you wish). The new diagnostics (if any) will be fed back to Syntastic the next time you press any key on the keyboard. So if you stop typing and just wait for the new diagnostics to come in, that _will not work_. You need to press some key for the GUI to update. Having to press a key to get the updates is unfortunate, but cannot be changed due to the way Vim internals operate; there is no way that a background task can update Vim's GUI after it has finished running. You _have to_ press a key. This will make YCM check for any pending diagnostics updates. You _can_ force a full, blocking compilation cycle with the `:YcmForceCompileAndDiagnostics` command (you may want to map that command to a key; try putting `nnoremap :YcmForceCompileAndDiagnostics` in your vimrc). Calling this command will force YCM to immediately recompile your file and display any new diagnostics it encounters. Do note that recompilation with this command may take a while and during this time the Vim GUI _will_ be blocked. After the errors are displayed by Syntastic, it will display a short diagnostic message when you move your cursor to the line with the error. You can get a detailed diagnostic message with the `d` key mapping (can be changed in the options) YCM provides when your cursor is on the line with the diagnostic. You can also see the full diagnostic message for all the diagnostics in the current file in Vim's `locationlist`, which can be opened with the `:lopen` and `:lclose` commands. A good way to toggle the display of the `locationlist` with a single key mapping is provided by another (very small) Vim plugin called [ListToggle][] (which also makes it possible to change the height of the `locationlist` window), also written by yours truly. TODO: extending the semantic engine for other langs Options ------- All options have reasonable defaults so if the plug-in works after installation you don't need to change any options. These options can be configured in your [vimrc script][vimrc] by including a line like this: let g:ycm_min_num_of_chars_for_completion = 1 Note that after changing an option in your [vimrc script] [vimrc] you have to restart Vim for the changes to take effect. ### The `g:ycm_min_num_of_chars_for_completion` option This option controls the number of characters the user needs to type before completion suggestions are triggered. For example, if the option is set to `2`, then when the user types a second alphanumeric character after a whitespace character, completion suggestions will be triggered. Default: `2` let g:ycm_min_num_of_chars_for_completion = 2 ### The `g:ycm_filetypes_to_completely_ignore` option This option controls for which Vim filetypes (see `:h filetype`) should YCM be turned off. The option value should be a Vim dictionary with keys being filetype strings (like `python`, `cpp` etc) and values being unimportant (the dictionary is used like a hash set, meaning that only the keys matter). The listed filetypes will be completely ignored by YCM, meaning that neither the identifier-based completion engine nor the semantic engine will operate in files of those filetypes. You can get the filetype of the current file in Vim with `:set ft?`. Default: `{notes: 1, markdown: 1, text: 1}` let g:ycm_filetypes_to_completely_ignore = { \ 'notes' : 1, \ 'markdown' : 1, \ 'text' : 1, \} ### The `g:ycm_filetype_specific_completion_to_disable` option This option controls for which Vim filetypes (see `:h filetype`) should the YCM semantic completion engine be turned off. The option value should be a Vim dictionary with keys being filetype strings (like `python`, `cpp` etc) and values being unimportant (the dictionary is used like a hash set, meaning that only the keys matter). The listed filetypes will be ignored by the YCM semantic completion engine, but the identifier-based completion engine will still trigger in files of those filetypes. Note that even if semantic completion is not turned off for a specific filetype, you will not get semantic completion if the semantic engine does not support that filetype. Currently, the semantic engine only supports the `c`, `cpp`, `objc` and `objcpp` filetypes. You can get the filetype of the current file in Vim with `:set ft?`. Default: `{}` let g:ycm_filetype_specific_completion_to_disable = {} ### The `g:ycm_allow_changing_updatetime` option When this option is set to `1`, YCM will change the `updatetime` Vim option to `2000` (see `:h updatetime`). This may conflict with some other plugins you have (but it's unlikely). The `updatetime` option is the number of milliseconds that have to pass before Vim's `CursorHold` (see `:h CursorHold`) event fires. YCM runs the completion engines' "file comprehension" systems in the background on every such event; the identifier-based engine collects the identifiers whereas the semantic engine compiles the file to build an AST. The Vim default of `4000` for `updatetime` is a bit long, so YCM reduces this. Set this option to `0` to force YCM to leave your `updatetime` setting alone. Default: `1` let g:ycm_allow_changing_updatetime = 1 ### The `g:ycm_add_preview_to_completeopt` option When this option is set to `1`, YCM will add the `preview` string to Vim's `completeopt` option (see `:h completeopt`). If your `completeopt` option already has `preview` set, there will be no effect. You can see the current state of your `completeopt` setting with `:set completeopt?` (yes, the question mark is important). When `preview` is present in `completeopt`, YCM will use the `preview` window at the top of the file to store detailed information about the current completion candidate (but only if the candidate came from the semantic engine). For instance, it would show the full function prototype and all the function overloads in the window if the current completion is a function name. Default: `0` let g:ycm_add_preview_to_completeopt = 0 ### The `g:ycm_autoclose_preview_window_after_completion` option When this option is set to `1`, YCM will auto-close the `preview` window after the user accepts the offered completion string. If there is no `preview` window triggered because there is no `preview` string in `completeopt`, this option is irrelevant. See the `g:ycm_add_preview_to_completeopt` option for more details. Default: `0` let g:ycm_autoclose_preview_window_after_completion = 0 ### The `g:ycm_max_diagnostics_to_display` option This option controls the maximum number of diagnostics shown to the user when errors or warnings are detected in the file. This option is only relevant if you are using the semantic completion engine and have installed the version of the Syntastic plugin that supports YCM. Default: `30` let g:ycm_max_diagnostics_to_display = 30 ### The `g:ycm_key_select_completion` option This option controls the key mapping used to select the first completion string. Invoking it repeatedly cycles forward through the completion list. Default: `` let g:ycm_key_select_completion = '' ### The `g:ycm_key_previous_completion` option This option controls the key mapping used to select the previous completion string. Invoking it repeatedly cycles backwards through the completion list. Note that the default of `` means Shift-TAB. Also note that the default mapping will probably only work in GUI Vim (Gvim or MacVim) and not in plain console Vim because the terminal usually does not forward modifier key combinations to Vim. Default: `` let g:ycm_key_previous_completion = '' ### The `g:ycm_key_invoke_completion` option This option controls the key mapping used to invoke the completion menu for semantic completion. By default, semantic completion is trigged automatically after typing `.`, `->` and `::` in insert mode (if semantic completion support has been compiled in). This key mapping can be used to trigger semantic completion anywhere. Useful for searching for top-level functions and classes. Note that the default of `` means Ctrl-Space. Also note that the default mapping will probably only work in GUI Vim (Gvim or MacVim) and not in plain console Vim because the terminal usually does not forward modifier key combinations to Vim. Default: `` let g:ycm_key_invoke_completion = '' ### The `g:ycm_key_detailed_diagnostics` option This option controls the key mapping used to show the full diagnostic text when the user's cursor is on the line with the diagnostic. Default: `d` let g:ycm_key_detailed_diagnostics = 'd' ### The `g:ycm_global_ycm_extra_conf` option Normally, YCM searches for a `.ycm_extra_conf.py` file for compilation flags (see the User Guide for more details on how this works). You can use this option to override this searching behavior by providing a full, absolute path to a global `.ycm_extra_conf.py` file (although you can call the global file whatever you want). You can place such a global file anywhere in your filesystem. Default: `` let g:ycm_global_ycm_extra_conf = '' FAQ --- ### I get a linker warning regarding `libpython` on Mac when compiling YCM If the warning is `ld: warning: path '/usr/lib/libpython2.7.dylib' following -L not a directory`, then feel free to ignore it; it's caused by a limitation of CMake and is not an issue. Everything should still work fine. ### I get a weird window at the top of my file when I use the semantic engine This is Vim's `preview` window. Vim uses it to show you extra information about something if such information is available. YCM provides Vim with such extra information. For instance, when you select a function in the completion list, the `preview` window will hold that function's prototype and the prototypes of any overloads of the function. It will stay there after you select the completion so that you can use the information about the parameters and their types to write the function call. If you would like this window to auto-close after you select a completion string, set the `g:ycm_autoclose_preview_window_after_completion` option to `1` in your `vimrc` file. If you don't want this window to ever show up, add `set completeopt-=preview` to your `vimrc`. Also make sure that the `g:ycm_add_preview_to_completeopt` option is set to `0`. ### It appears that YCM is not working In Vim, run `:messages` and carefully read the output. YCM will echo messages to the message log if it encounters problems. It's likely you misconfigured something and YCM is complaining about it. Also, you may want to run the `:YcmDebugInfo` command; it will make YCM spew out various debugging information, including the compile flags for the file if the file is a C-family language file and you have compiled in Clang support. ### I cannot get the Syntastic integration to work Try to update your version of Syntastic. At the time of writing (Jan 2013), the YCM integration is very recent and it's likely that your version of Syntastic does not have it. ### Sometimes it takes much longer to get semantic completions than normal This means that libclang (which YCM uses for C-family semantic completion) failed to compile your file's preamble. In other words, there was an error compiling some of the source code you pulled in through your header files. I suggest calling the `:YcmDiags` command to see what they were (even better, have Syntastic installed and call `:lopen`). Contact ------- If you have questions, bug reports, suggestions, etc. please use the [issue tracker][tracker]. The latest version is available at . The author's homepage is . License ------- This software is licensed under the [GPL v3 license][gpl]. © 2012 Strahinja Val Markovic <>. [Clang]: http://clang.llvm.org/ [vundle]: https://github.com/gmarik/vundle#about [pathogen]: https://github.com/tpope/vim-pathogen#pathogenvim [clang-download]: http://llvm.org/releases/download.html#3.2 [brew]: http://mxcl.github.com/homebrew/ [cmake-download]: http://www.cmake.org/cmake/resources/software.html [macvim]: http://code.google.com/p/macvim/#Download [vimrc]: http://vimhelp.appspot.com/starting.txt.html#vimrc [gpl]: http://www.gnu.org/copyleft/gpl.html [vim]: http://www.vim.org/ [syntastic]: https://github.com/scrooloose/syntastic [flags_example]: https://github.com/Valloric/YouCompleteMe/blob/master/cpp/ycm/.ycm_extra_conf.py [compdb]: http://clang.llvm.org/docs/JSONCompilationDatabase.html [subsequence]: http://en.wikipedia.org/wiki/Subsequence [listtoggle]: https://github.com/Valloric/ListToggle