#782 - Do not set the build directory for clang-tidy for header files, which does not work

ale_linters/cpp/clangtidy.vim

@@ -14,15 +14,28 @@ function! ale_linters#cpp#clangtidy#GetExecutable(buffer) abort
     return ale#Var(a:buffer, 'cpp_clangtidy_executable')
 endfunction
 
-function! ale_linters#cpp#clangtidy#GetCommand(buffer) abort
-    let l:checks = join(ale#Var(a:buffer, 'cpp_clangtidy_checks'), ',')
+function! s:GetBuildDirectory(buffer) abort
+    " Don't include build directory for header files, as compile_commands.json
+    " files don't consider headers to be translation units, and provide no
+    " commands for compiling header files.
+    if expand('#' . a:buffer) =~# '\v\.(h|hpp)$'
+        return ''
+    endif
+
     let l:build_dir = ale#Var(a:buffer, 'c_build_dir')
 
     " c_build_dir has the priority if defined
-    if empty(l:build_dir)
-        let l:build_dir = ale#c#FindCompileCommands(a:buffer)
+    if !empty(l:build_dir)
+        return l:build_dir
     endif
 
+    return ale#c#FindCompileCommands(a:buffer)
+endfunction
+
+function! ale_linters#cpp#clangtidy#GetCommand(buffer) abort
+    let l:checks = join(ale#Var(a:buffer, 'cpp_clangtidy_checks'), ',')
+    let l:build_dir = s:GetBuildDirectory(a:buffer)
+
     " Get the extra options if we couldn't find a build directory.
     let l:options = empty(l:build_dir)
     \   ? ale#Var(a:buffer, 'cpp_clangtidy_options')

test/command_callback/test_clang_tidy_command_callback.vader

@@ -12,6 +12,8 @@ Before:
 
   runtime ale_linters/cpp/clangtidy.vim
 
+  call ale#test#SetFilename('test.cpp')
+
 After:
   unlet! b:ale_c_build_dir
   unlet! b:ale_cpp_clangtidy_checks
@@ -68,6 +70,24 @@ Execute(The build directory setting should override the options):
   \   . ' -checks=''*'' %s -p ' . ale#Escape('/foo/bar'),
   \ ale_linters#cpp#clangtidy#GetCommand(bufnr(''))
 
+Execute(The build directory should be ignored for header files):
+  call ale#test#SetFilename('test.h')
+
+  let b:ale_c_build_dir = '/foo/bar'
+  let b:ale_cpp_clangtidy_options = '-Wall'
+
+  AssertEqual
+  \ ale#Escape('clang-tidy')
+  \   . ' -checks=''*'' %s -- -Wall',
+  \ ale_linters#cpp#clangtidy#GetCommand(bufnr(''))
+  \
+  call ale#test#SetFilename('test.hpp')
+
+  AssertEqual
+  \ ale#Escape('clang-tidy')
+  \   . ' -checks=''*'' %s -- -Wall',
+  \ ale_linters#cpp#clangtidy#GetCommand(bufnr(''))
+
 Execute(The executable should be configurable):
   let b:ale_cpp_clangtidy_executable = 'foobar'