Enable C flag parsing by default

The options for parsing `make -n` and `compile_commands.json` flags
are now enabled by default, so people can start getting better flags
for their files by default.

`compile_commands.json` flags are now preferred over `make -n` results,
to make the options work better by default.

README.md

@@ -816,6 +816,13 @@ setting.  Consult the documentation for that setting for more information.
 `b:ale_linters` can be used to select which tools you want to run, say if you
 want to use only `gcc` for one project, and only `clang` for another.
 
+ALE will attempt to parse `make -n` when a `Makefile` is found or load the flags
+for files from `compile_commands.json` files. See `:help g:ale_c_parse_makefile`
+and `:help g:ale_c_parse_compile_commands` for more information. See Clang's
+documentation for [compile_commands.json files](https://clang.llvm.org/docs/JSONCompilationDatabase.html).
+You should strongly consider generating them in your builds, which is easy to
+do with CMake.
+
 You may also configure buffer-local settings for linters with project-specific
 vimrc files. [local_vimrc](https://github.com/LucHermitte/local_vimrc) can be
 used for executing local vimrc files which can be shared in your project.

autoload/ale/c.vim

@@ -1,8 +1,8 @@
 " Author: gagbo <gagbobada@gmail.com>, w0rp <devw0rp@gmail.com>, roel0 <postelmansroel@gmail.com>
 " Description: Functions for integrating with C-family linters.
 
-call ale#Set('c_parse_makefile', 0)
-call ale#Set('c_parse_compile_commands', 0)
+call ale#Set('c_parse_makefile', 1)
+call ale#Set('c_parse_compile_commands', 1)
 let s:sep = has('win32') ? '\' : '/'
 
 " Set just so tests can override it.
@@ -334,10 +334,6 @@ endfunction
 function! ale#c#GetCFlags(buffer, output) abort
     let l:cflags = v:null
 
-    if ale#Var(a:buffer, 'c_parse_makefile') && !empty(a:output)
-        let l:cflags = ale#c#ParseCFlagsFromMakeOutput(a:buffer, a:output)
-    endif
-
     if ale#Var(a:buffer, 'c_parse_compile_commands')
         let [l:root, l:json_file] = ale#c#FindCompileCommands(a:buffer)
 
@@ -346,6 +342,12 @@ function! ale#c#GetCFlags(buffer, output) abort
         endif
     endif
 
+    if ale#Var(a:buffer, 'c_parse_makefile')
+    \&& !empty(a:output)
+    \&& !empty(l:cflags)
+        let l:cflags = ale#c#ParseCFlagsFromMakeOutput(a:buffer, a:output)
+    endif
+
     if l:cflags is v:null
         let l:cflags = ale#c#IncludeOptions(ale#c#FindLocalHeaderPaths(a:buffer))
     endif

doc/ale-c.txt

@@ -37,7 +37,7 @@ g:ale_c_build_dir                                           *g:ale_c_build_dir*
 g:ale_c_parse_compile_commands                 *g:ale_c_parse_compile_commands*
                                                *b:ale_c_parse_compile_commands*
   Type: |Number|
-  Default: `0`
+  Default: `1`
 
   If set to `1`, ALE will parse `compile_commands.json` files to automatically
   determine flags for C or C++ compilers. ALE will first search for the
@@ -45,19 +45,23 @@ g:ale_c_parse_compile_commands                 *g:ale_c_parse_compile_commands*
   `compile_commands.json` files in the directories for
   |g:ale_c_build_dir_names|.
 
-  If |g:ale_c_parse_makefile| or |b:ale_c_parse_makefile| is set to `1`, the
-  output of `make -n` will be preferred over `compile_commands.json` files.
-
 
 g:ale_c_parse_makefile                                 *g:ale_c_parse_makefile*
                                                        *b:ale_c_parse_makefile*
   Type: |Number|
-  Default: `0`
+  Default: `1`
 
   If set to `1`, ALE will run `make -n` to automatically determine flags to
   set for C or C++ compilers. This can make it easier to determine the correct
   build flags to use for different files.
 
+  You might want to disable this option if `make -n` takes too long to run for
+  projects you work on.
+
+  If |g:ale_c_parse_compile_commands| or |b:ale_c_parse_compile_commands| is
+  set to `1`, flags taken from `compile_commands.json` will be preferred over
+  `make -n` output.
+
 
 ===============================================================================
 astyle                                                           *ale-c-astyle*