Learn-Vim/ch19_compile.md

Ch19. Compile

Compiling is an important subject for many languages. In this chapter, you will learn how to compile from Vim. You will also look at ways to take advantage of Vim's :make command.

Compile From the Command Line

You can use the bang operator (!) to compile. If you need to compile your .cpp file with g++, run:

:!g++ hello.cpp -o hello

However, having to manually type the filename and the output filename each time is error-prone and tedious. A makefile is the way to go.

The Make Command

Vim has a :make command to run a makefile. When you run it, Vim looks for a makefile in the current directory to execute.

Create a file named makefile in the current directory and put these inside:

all:
	echo "Hello all"
foo:
	echo "Hello foo"
list_pls:
	ls

Run this from Vim:

:make

Vim executes it the same way as when you're running it from the terminal. The :make command accepts parameter just like the terminal make command. Run:

:make foo
" Outputs "Hello foo"

:make list_pls
" Outputs the ls command result

The :make command uses Vim's quickfix to store any error if you run a bad command. Let's run a nonexisting target:

:make dontexist

You should see an error running that command. To view that error, run the quickfix command :copen to view the quickfix window:

|| make: *** No rule to make target `dontexist'.  Stop.

Compiling With Make

Let's use the makefile to compile a basic .cpp program. First, let's create a hello.cpp file:

#include <iostream>

int main() {
    std::cout << "Hello!\\n";
    return 0;
}

Update your makefile to build and run a .cpp file:

all:
	echo "build, run"
build:
	g++ hello.cpp -o hello
run:
	./hello

Now run:

:make build

The g++ compiles ./hello.cpp and creates ./hello. Then run:

:make run

You should see "Hello!" printed on the terminal.

Different Make Program

When you run :make, Vim actually runs whatever command that is set under the makeprg option. If you run :set makeprg?, you'll see:

makeprg=make

The default :make command is the make external command. To change the :make command to execute g++ {your-file-name} each time you run it, run:

:set makeprg=g++\ %

The \ is to escape the space after g++. The % symbol in Vim represents the current file. The command g++\\ % is equivalent to running g++ hello.cpp.

Go to ./hello.cpp then run :make. Vim compiles hello.cpp and creates a.out because you didn't specify the output. Let's refactor it so it will name the compiled output with the name of the original file minus the extension. Run or add this to vimrc:

set makeprg=g++\ %\ -o\ %<

The breakdown:

• g++\ % is the same as above. It is equivalent to running g++ <your-file>.
• -o is the output option.
• %< in Vim represents the current file name without an extension (hello.cpp becomes hello).

When you run :make from inside ./hello.cpp, it is compiled into ./hello. To quickly execute ./hello from inside ./hello.cpp, run :!./%<. Again, this is the same as running :!./{current-file-name-minus-the-extension}.

For more, check out :h :compiler and :h write-compiler-plugin.

Auto-compile on Save

You can make life even easier by automating compilation. Recall that you can use Vim's autocmd to trigger automatic actions based on certain events. To automatically compile .cpp files on each save add this on your vimrc:

autocmd BufWritePost *.cpp make

Each time you save inside a .cpp file, Vim executes the make command.

Switching Compiler

Vim has a :compiler command to quickly switch compilers. Your Vim build probably comes with several pre-built compiler configurations. To check what compilers you have, run:

:e $VIMRUNTIME/compiler/<Tab>

You should see a list of compilers for different programming languages.

To use the :compiler command, suppose you have a ruby file, hello.rb and inside it has:

puts "Hello ruby"

Recall that if you run :make, Vim executes whatever command is assigned to makeprg (default is make). If you run:

:compiler ruby

Vim runs the $VIMRUNTIME/compiler/ruby.vim script and changes the makeprg to use the ruby command. Now if you run :set makeprg?, it should say makeprg=ruby (this depends on what is inside your $VIMRUNTIME/compiler/ruby.vim file or if you have another custom ruby compilers. Yours might be different). The :compiler {your-lang} command allows you to switch to different compilers quickly. This is useful if your project uses multiple languages.

You don't have to use the :compiler and makeprg to compile a program. You can run a test script, lint a file, send a signal, or anything you want.

Creating a Custom Compiler

Let's create a simple Typescript compiler. Install Typescript (npm install -g typescript) to your machine. You should now have the tsc command. If you haven't played with typescript before, tsc compiles a Typescript file into a Javascript file. Suppose that you have a file, hello.ts:

const hello = "hello";
console.log(hello);

If you run tsc hello.ts, it will compile into hello.js. However, if you have the following expressions inside hello.ts:

const hello = "hello";
hello = "hello again";
console.log(hello);

This will throw an error because you can't mutate a const variable. Running tsc hello.ts will throw an error:

hello.ts:2:1 - error TS2588: Cannot assign to 'person' because it is a constant.

2 person = "hello again";
  ~~~~~~


Found 1 error.

To create a simple Typescript compiler, in your ~/.vim/ directory, add a compiler directory (~/.vim/compiler/), then create a typescript.vim file (~/.vim/compiler/typescript.vim). Put this inside:

CompilerSet makeprg=tsc
CompilerSet errorformat=%f:\ %m

The first line sets the makeprg to run the tsc command. The second line sets the error format to display the file (%f), followed by a literal colon (:) and an escaped space (\ ), followed by the error message (%m). To learn more about the error formatting, check out :h errorformat.

You should also read some of the pre-made compilers to see how others do it. Check out :e $VIMRUNTIME/compiler/<some-language>.vim.

Because some plugins may interfere with the Typescript file, let's open the hello.ts without any plugin, using the --noplugin flag:

vim --noplugin hello.ts

Check the makeprg:

:set makeprg?

It should say the default make program. To use the new Typescript compiler, run:

:compiler typescript

When you run :set makeprg?, it should say tsc now. Let's put it to the test. Run:

:make %

Recall that % means the current file. Watch your Typescript compiler work as expected! To see the list of error(s), run :copen.

Async Compiler

Sometimes compiling can take a long time. You don't want to be staring at a frozen Vim while waiting for your compilation process to finish. Wouldn't it be nice if you can compile asynchronously so you can still use Vim during compilation?

Luckily there are plugins to run async processes. The two big ones are:

• vim-dispatch
• asyncrun.vim

In the remaining of this chapter, I will go over vim-dispatch, but I would strongly encourage you to try all of them out there.

Vim and NeoVim actually supports async jobs, but they are beyond the scope of this chapter. If you're curious, check out :h job-channel-overview.txt.

Plugin: Vim-dispatch

Vim-dispatch has several commands, but the two main ones are :Make and :Dispatch commands.

Async Make

Vim-dispatch's :Make command is similar to Vim's :make, but it runs asynchronously. If you are in a Javascript project and you need to run npm t, you might attempt to set your makeprg to be:

:set makeprg=npm\\ t

If you run:

:make

Vim will execute npm t, but you will be staring at the frozen screen while your JavaScript test runs. With vim-dispatch, you can just run:

:Make

Vim will run npm t asynchronously. This way, while npm t is running on a background process, you can continue doing whatever you were doing. Awesome!

Async Dispatch

The :Dispatch command is like the :compiler and the :! command. It can run any external command asynchronously in Vim.

Assume that you are inside a ruby spec file and you need to run a test. Run:

:Dispatch bundle exec rspec %

Vim will asynchronously run the rspec command against the current file (%).

Automating Dispatch

Vim-dispatch has b:dispatch buffer variable that you can configure to evaluate specific command automatically. You can leverage it with autocmd. If you add this in your vimrc:

autocmd BufEnter *_spec.rb let b:dispatch = 'bundle exec rspec %'

Now each time you enter a file (BufEnter) that ends with _spec.rb, running :Dispatch automatically executes bundle exec rspec {your-current-ruby-spec-file}.

Learn Compile the Smart Way

In this chapter, you learned that you can use the make and compiler commands to run any process from inside Vim asynchronously to complement your programming workflow. Vim's ability to extend itself with other programs makes it powerful.