Set GCC flags appropriately for older versions

ale_linters/cpp/gcc.vim

@@ -3,16 +3,17 @@
 
 " Set this option to change the GCC options for warnings for C.
 if !exists('g:ale_cpp_gcc_options')
-    " added c++14 standard support
-    " POSIX thread and standard c++ thread and atomic library Linker
-    " let g:ale_cpp_gcc_options = '-std=c++1z' for c++17
-    " for previous version and default, you can just use
-    " let g:ale_cpp_gcc_options = '-Wall'
-    " for more see man pages of gcc
-    " $ man g++
-    " make sure g++ in your $PATH
-    " Add flags according to your requirements
-    let g:ale_cpp_gcc_options = '-std=c++14 -Wall'
+    let s:version = ale#handlers#gcc#ParseGCCVersion(systemlist('gcc --version'))
+
+    if !empty(s:version) && ale#semver#GreaterOrEqual(s:version, [4, 9, 0])
+        " Use c++14 support in 4.9 and above.
+        let g:ale_cpp_gcc_options = '-std=c++14 -Wall'
+    else
+        " Use c++1y in older versions.
+        let g:ale_cpp_gcc_options = '-std=c++1y -Wall'
+    endif
+
+    unlet! s:version
 endif
 
 function! ale_linters#cpp#gcc#GetCommand(buffer) abort

autoload/ale/handlers/gcc.vim

@@ -26,6 +26,18 @@ function! s:RemoveUnicodeQuotes(text) abort
     return l:text
 endfunction
 
+function! ale#handlers#gcc#ParseGCCVersion(lines) abort
+    for l:line in a:lines
+        let l:match = matchstr(l:line, '\d\.\d\.\d')
+
+        if !empty(l:match)
+            return ale#semver#Parse(l:match)
+        endif
+    endfor
+
+    return []
+endfunction
+
 function! ale#handlers#gcc#HandleGCCFormat(buffer, lines) abort
     let l:include_pattern = '\v^(In file included | *)from ([^:]*):(\d+)'
     let l:include_lnum = 0

test/handler/test_gcc_handler.vader

@@ -66,3 +66,14 @@ Execute(GCC errors from included files should be parsed correctly):
   \   ' other_bad_type y;',
   \   ' ^',
   \ ])
+
+Execute(GCC versions should be parsed correctly):
+  AssertEqual [4, 9, 1], ale#handlers#gcc#ParseGCCVersion([
+  \ 'g++ (GCC) 4.9.1 20140922 (Red Hat 4.9.1-10)',
+  \])
+  AssertEqual [4, 8, 4], ale#handlers#gcc#ParseGCCVersion([
+  \ 'gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4',
+  \ 'Copyright (C) 2013 Free Software Foundation, Inc.',
+  \ 'This is free software; see the source for copying conditions.  There is NO',
+  \ 'warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.',
+  \])