cc: fix using '-x c*-header' for header files with GCC. (#4334)

Gcc does not support `x c*-header` when using `-` as input filename,
which is what ALE does.

Rework the feature to only use `-x c*-header` flag when using Clang and
not GCC.

The feature is now also controlled with the variable
`g:ale_c_cc_use_header_lang_flag` and
`g:ale_cpp_cc_use_header_lang_flag`.

ale_linters/c/cc.vim

@@ -3,6 +3,7 @@
 
 call ale#Set('c_cc_executable', '<auto>')
 call ale#Set('c_cc_options', '-std=c11 -Wall')
+call ale#Set('c_cc_use_header_lang_flag', -1)
 call ale#Set('c_cc_header_exts', ['h'])
 
 function! ale_linters#c#cc#GetExecutable(buffer) abort
@@ -23,8 +24,6 @@ endfunction
 function! ale_linters#c#cc#GetCommand(buffer, output) abort
     let l:cflags = ale#c#GetCFlags(a:buffer, a:output)
     let l:ale_flags = ale#Var(a:buffer, 'c_cc_options')
-    let l:header_exts = ale#Var(a:buffer, 'c_cc_header_exts')
-    let l:lang_flag = ale#c#GetLanguageFlag(a:buffer, l:header_exts, 'c')
 
     if l:cflags =~# '-std='
         let l:ale_flags = substitute(
@@ -34,6 +33,18 @@ function! ale_linters#c#cc#GetCommand(buffer, output) abort
         \   'g')
     endif
 
+    " Select the correct language flag depending on the executable, options
+    " and file extension
+    let l:executable = ale_linters#c#cc#GetExecutable(a:buffer)
+    let l:use_header_lang_flag = ale#Var(a:buffer, 'c_cc_use_header_lang_flag')
+    let l:header_exts = ale#Var(a:buffer, 'c_cc_header_exts')
+    let l:lang_flag = ale#c#GetLanguageFlag(
+    \   a:buffer,
+    \   l:executable,
+    \   l:use_header_lang_flag,
+    \   l:header_exts,
+    \   'c')
+
     " -iquote with the directory the file is in makes #include work for
     "  headers in the same directory.
     "

ale_linters/cpp/cc.vim

@@ -3,6 +3,7 @@
 
 call ale#Set('cpp_cc_executable', '<auto>')
 call ale#Set('cpp_cc_options', '-std=c++14 -Wall')
+call ale#Set('cpp_cc_use_header_lang_flag', -1)
 call ale#Set('cpp_cc_header_exts', ['h', 'hpp'])
 
 function! ale_linters#cpp#cc#GetExecutable(buffer) abort
@@ -23,8 +24,6 @@ endfunction
 function! ale_linters#cpp#cc#GetCommand(buffer, output) abort
     let l:cflags = ale#c#GetCFlags(a:buffer, a:output)
     let l:ale_flags = ale#Var(a:buffer, 'cpp_cc_options')
-    let l:header_exts = ale#Var(a:buffer, 'cpp_cc_header_exts')
-    let l:lang_flag = ale#c#GetLanguageFlag(a:buffer, l:header_exts, 'c++')
 
     if l:cflags =~# '-std='
         let l:ale_flags = substitute(
@@ -34,6 +33,18 @@ function! ale_linters#cpp#cc#GetCommand(buffer, output) abort
         \   'g')
     endif
 
+    " Select the correct language flag depending on the executable, options
+    " and file extension
+    let l:executable = ale_linters#cpp#cc#GetExecutable(a:buffer)
+    let l:use_header_lang_flag = ale#Var(a:buffer, 'cpp_cc_use_header_lang_flag')
+    let l:header_exts = ale#Var(a:buffer, 'cpp_cc_header_exts')
+    let l:lang_flag = ale#c#GetLanguageFlag(
+    \   a:buffer,
+    \   l:executable,
+    \   l:use_header_lang_flag,
+    \   l:header_exts,
+    \   'c++')
+
     " -iquote with the directory the file is in makes #include work for
     "  headers in the same directory.
     "

autoload/ale/c.vim

@@ -586,13 +586,37 @@ function! ale#c#IncludeOptions(include_paths) abort
     return join(l:option_list)
 endfunction
 
-" Get the language flag depending on if the file is a header or not.
-function! ale#c#GetLanguageFlag(buffer, header_exts, linter_lang) abort
-    let l:buf_ext = expand('#' . a:buffer . ':e')
-
-    if index(a:header_exts, l:buf_ext) >= 0
-        return a:linter_lang . '-header'
+" Get the language flag depending on on the executable, options and
+" file extension
+function! ale#c#GetLanguageFlag(
+\   buffer,
+\   executable,
+\   use_header_lang_flag,
+\   header_exts,
+\   linter_lang_flag
+\) abort
+    " Use only '-header' if the executable is 'clang' by default
+    if a:use_header_lang_flag == -1
+        let l:use_header_lang_flag = a:executable =~# 'clang'
+    else
+        let l:use_header_lang_flag = a:use_header_lang_flag
     endif
 
-    return a:linter_lang
+    " If we don't use the header language flag, return the default linter
+    " language flag
+    if !l:use_header_lang_flag
+        return a:linter_lang_flag
+    endif
+
+    " Get the buffer file extension
+    let l:buf_ext = expand('#' . a:buffer . ':e')
+
+    " If the buffer file is an header according to its extension, use
+    " the linter language flag + '-header', ex: 'c-header'
+    if index(a:header_exts, l:buf_ext) >= 0
+        return a:linter_lang_flag . '-header'
+    endif
+
+    " Else, use the default linter language flag
+    return a:linter_lang_flag
 endfunction

doc/ale-c.txt

@@ -133,7 +133,30 @@ g:ale_c_cc_options                                         *g:ale_c_cc_options*
   Type: |String|
   Default: `'-std=c11 -Wall'`
 
-  This variable can be change to modify flags given to the C compiler.
+  This variable can be changed to modify flags given to the C compiler.
+
+
+g:ale_c_cc_use_header_lang_flag               *g:ale_c_cc_use_header_lang_flag*
+                                              *b:ale_c_cc_use_header_lang_flag*
+  Type: |Number|
+  Default: `-1`
+
+  By default, ALE will use `'-x c-header'` instead of `'-x c'` for header files
+  when using Clang.
+
+  This variable can be changed to manually activate or deactivate this flag
+  for header files.
+
+  - When set to `-1`, the default beviour is used, `'-x c-header'` is used with
+    Clang and `'-x c'` is used with other compilers.
+  - When set to `0`, the flag is deactivated, `'-x c'` is always used
+    independently of the compiler.
+  - When set to `1`, the flag is activated, `'-x c-header'` is always used
+    independently of the compiler.
+
+  Gcc does not support `'-x c-header'` when using `'-'` as input filename,
+  which is what ALE does. This why, by default, ALE only uses `'-x c-header'`
+  with Clang.
 
 
 g:ale_c_cc_header_exts                                 *g:ale_c_cc_header_exts*
@@ -141,10 +164,11 @@ g:ale_c_cc_header_exts                                 *g:ale_c_cc_header_exts*
   Type: |List|
   Default: `['h']`
 
-  This variable can be change to modify the list of extensions of the files
+  This variable can be changed to modify the list of extensions of the files
   considered as header files.
 
-  ALE will use `'-x c-header'` instead of `'-x c'` for header files.
+  This variable is only used when `'-x c-header'` is used instead of `'-x c'`,
+  see |ale_c_cc_use_header_lang_flag|.
 
 
 ===============================================================================

doc/ale-cpp.txt

@@ -62,7 +62,30 @@ g:ale_cpp_cc_options                                     *g:ale_cpp_cc_options*
   Type: |String|
   Default: `'-std=c++14 -Wall'`
 
-  This variable can be change to modify flags given to the C++ compiler.
+  This variable can be changed to modify flags given to the C++ compiler.
+
+
+g:ale_cpp_cc_use_header_lang_flag           *g:ale_cpp_cc_use_header_lang_flag*
+                                            *b:ale_cpp_cc_use_header_lang_flag*
+  Type: |Number|
+  Default: `-1`
+
+  By default, ALE will use `'-x c++-header'` instead of `'-x c++'` for header
+  files when using Clang.
+
+  This variable can be changed to manually activate or deactivate this flag
+  for header files.
+
+  - When set to `-1`, the default beviour is used, `'-x c++-header'` is used with
+    Clang and `'-x c++'` is used with other compilers.
+  - When set to `0`, the flag is deactivated, `'-x c++'` is always used
+    independently of the compiler.
+  - When set to `1`, the flag is activated, `'-x c++-header'` is always used
+    independently of the compiler.
+
+  Gcc does not support `'-x c++-header'` when using `'-'` as input filename,
+  which is what ALE does. This why, by default, ALE only uses `'-x c++-header'`
+  with Clang.
 
 
 g:ale_cpp_cc_header_exts                             *g:ale_cpp_cc_header_exts*
@@ -70,10 +93,11 @@ g:ale_cpp_cc_header_exts                             *g:ale_cpp_cc_header_exts*
   Type: |List|
   Default: `['h', 'hpp']`
 
-  This variable can be change to modify the list of extensions of the files
+  This variable can be changed to modify the list of extensions of the files
   considered as header files.
 
-  ALE will use `'-x c++-header'` instead of `'-x c++'` for header files.
+  This variable is only used when `'-x c++-header'` is used instead of `'-x c++'`,
+  see |ale_cpp_cc_use_header_lang_flag|.
 
 
 ===============================================================================

test/linter/test_c_cc.vader

@@ -54,18 +54,41 @@ Execute(The -std flag should be replaced by parsed C flags):
 
   AssertLinter 'gcc', ale#Escape('gcc') . b:command_tail
 
-Execute(The header files should use -x c-header):
+Execute(gcc should not use -x c-header with header files by default):
+  call ale#test#SetFilename('../test-files/c/makefile_project/subdir/test.h')
+
+  AssertLinter 'gcc', ale#Escape('gcc') . b:command_tail
+
+Execute(clang should use -x c-header with header files by default):
+  let g:executable_map = {'clang': 1}
+  let b:command_tail = substitute(b:command_tail, '-x c', '-x c-header', '')
+
+  call ale#test#SetFilename('../test-files/c/makefile_project/subdir/test.h')
+
+  AssertLinter 'clang', ale#Escape('clang') . b:command_tail
+
+Execute(gcc should use -x c-header with header files if configured to do so):
+  let b:ale_c_cc_use_header_lang_flag = 1
   let b:command_tail = substitute(b:command_tail, '-x c', '-x c-header', '')
 
   call ale#test#SetFilename('../test-files/c/makefile_project/subdir/test.h')
 
   AssertLinter 'gcc', ale#Escape('gcc') . b:command_tail
 
+Execute(clang should not use -x c-header with header files if configured to do so):
+  let g:executable_map = {'clang': 1}
+  let b:ale_c_cc_use_header_lang_flag = 0
+
+  call ale#test#SetFilename('../test-files/c/makefile_project/subdir/test.h')
+
+  AssertLinter 'clang', ale#Escape('clang') . b:command_tail
+
 Execute(The header file extensions should be configurable):
+  let g:executable_map = {'clang': 1}
   let b:command_tail = substitute(b:command_tail, '-x c', '-x c-header', '')
 
   call ale#assert#SetUpLinterTest('c', 'cc')
   let b:ale_c_cc_header_exts = ['json']
   call ale#test#SetFilename('../test-files/c/json_project/build/compile_commands.json')
 
-  AssertLinter 'gcc', ale#Escape('gcc') . b:command_tail
+  AssertLinter 'clang', ale#Escape('clang') . b:command_tail

test/linter/test_cpp_cc.vader

@@ -54,18 +54,41 @@ Execute(The -std flag should be replaced by parsed C flags):
 
   AssertLinter 'gcc', ale#Escape('gcc') . b:command_tail
 
-Execute(The header files should use -x c++-header):
+Execute(gcc should not use -x c++-header with header files by default):
+  call ale#test#SetFilename('../test-files/c/hpp_file_project/test.hpp')
+
+  AssertLinter 'gcc', ale#Escape('gcc') . b:command_tail
+
+Execute(clang++ should use -x c++-header with header files by default):
+  let g:executable_map = {'clang++': 1}
+  let b:command_tail = substitute(b:command_tail, '-x c++', '-x c++-header', '')
+
+  call ale#test#SetFilename('../test-files/c/hpp_file_project/test.hpp')
+
+  AssertLinter 'clang++', ale#Escape('clang++') . b:command_tail
+
+Execute(gcc should use -x c-header with header files if configured to do so):
+  let b:ale_cpp_cc_use_header_lang_flag = 1
   let b:command_tail = substitute(b:command_tail, '-x c++', '-x c++-header', '')
 
   call ale#test#SetFilename('../test-files/c/hpp_file_project/test.hpp')
 
   AssertLinter 'gcc', ale#Escape('gcc') . b:command_tail
 
+Execute(clang should not use -x c-header with header files if configured to do so):
+  let g:executable_map = {'clang++': 1}
+  let b:ale_cpp_cc_use_header_lang_flag = 0
+
+  call ale#test#SetFilename('../test-files/c/hpp_file_project/test.hpp')
+
+  AssertLinter 'clang++', ale#Escape('clang++') . b:command_tail
+
 Execute(The header file extensions should be configurable):
+  let g:executable_map = {'clang++': 1}
   let b:command_tail = substitute(b:command_tail, '-x c++', '-x c++-header', '')
 
   call ale#assert#SetUpLinterTest('cpp', 'cc')
   let b:ale_cpp_cc_header_exts = ['json']
   call ale#test#SetFilename('../test-files/c/json_project/build/compile_commands.json')
 
-  AssertLinter 'gcc', ale#Escape('gcc') . b:command_tail
+  AssertLinter 'clang++', ale#Escape('clang++') . b:command_tail