Add support for Pod based SwiftLint (#2122)

It's common to add SwiftLint as a CocoaPod dependency, instead of as a global
binary. In this case we should use that version of SwiftLint before looking
for any others. Note that I'm also adding support for SwiftLint in ReactNative
projects here as well, where the Pods directory would be nested inside an ios
directory.

ale_linters/swift/swiftlint.vim

@@ -1,6 +1,24 @@
-" Author: David Mohundro <david@mohundro.com>
+" Author: David Mohundro <david@mohundro.com>, Gordon Fontenot <gordon@fonten.io>
 " Description: swiftlint for swift files
 
+call ale#Set('swift_swiftlint_executable', 'swiftlint')
+call ale#Set('swift_swiftlint_use_global', get(g:, 'ale_use_global_executables', 0))
+
+function! ale_linters#swift#swiftlint#GetExecutable(buffer) abort
+    return ale#node#FindExecutable(a:buffer, 'swift_swiftlint', [
+          \ 'Pods/SwiftLint/swiftlint',
+          \ 'ios/Pods/SwiftLint/swiftlint',
+          \ 'swiftlint',
+          \])
+endfunction
+
+function! ale_linters#swift#swiftlint#GetCommand(buffer) abort
+    let l:executable = ale_linters#swift#swiftlint#GetExecutable(a:buffer)
+    let l:args = 'lint --use-stdin'
+
+    return ale#Escape(l:executable)
+          \ . ' ' .l:args
+endfunction
 
 function! ale_linters#swift#swiftlint#Handle(buffer, lines) abort
     let l:pattern = '\v^([a-zA-Z]?:?[^:]+):(\d+):(\d+)?:? ([^:]+): (.+)$'
@@ -45,7 +63,7 @@ endfunction
 
 call ale#linter#Define('swift', {
 \   'name': 'swiftlint',
-\   'executable': 'swiftlint',
-\   'command': 'swiftlint lint --use-stdin',
+\   'executable_callback': 'ale_linters#swift#swiftlint#GetExecutable',
+\   'command_callback': 'ale_linters#swift#swiftlint#GetCommand',
 \   'callback': 'ale_linters#swift#swiftlint#Handle',
 \})

test/test_swiftlint_executable_detection.vader

@@ -0,0 +1,50 @@
+Before:
+  let g:ale_swift_swiftlint_executable = 'swiftlint_d'
+
+  call ale#test#SetDirectory('/testplugin/test')
+
+  runtime ale_linters/swift/swiftlint.vim
+
+After:
+  let g:ale_has_override = {}
+  let g:ale_swift_swiftlint_executable = 'swiftlint'
+  let g:ale_swift_swiftlint_use_global = 0
+
+  call ale#test#RestoreDirectory()
+  call ale#linter#Reset()
+
+Execute(Global installation should be the default executable):
+  call ale#test#SetFilename('swiftlint-test-files/global/testfile.swift')
+
+  AssertEqual
+  \ 'swiftlint_d',
+  \ ale_linters#swift#swiftlint#GetExecutable(bufnr(''))
+
+Execute(React Native apps using CocoaPods should take precedence over the default executable):
+  call ale#test#SetFilename('swiftlint-test-files/react-native/testfile.swift')
+
+  AssertEqual
+  \ ale#path#Simplify(g:dir . '/swiftlint-test-files/react-native/ios/Pods/SwiftLint/swiftlint'),
+  \ ale_linters#swift#swiftlint#GetExecutable(bufnr(''))
+
+Execute(CocoaPods installation should take precedence over the default executable):
+  call ale#test#SetFilename('swiftlint-test-files/cocoapods/testfile.swift')
+
+  AssertEqual
+  \ ale#path#Simplify(g:dir . '/swiftlint-test-files/cocoapods/Pods/SwiftLint/swiftlint'),
+  \ ale_linters#swift#swiftlint#GetExecutable(bufnr(''))
+
+Execute(Top level CocoaPods installation should take precedence over React Native installation):
+  call ale#test#SetFilename('swiftlint-test-files/cocoapods-and-react-native/testfile.swift')
+
+  AssertEqual
+  \ ale#path#Simplify(g:dir . '/swiftlint-test-files/cocoapods-and-react-native/Pods/SwiftLint/swiftlint'),
+  \ ale_linters#swift#swiftlint#GetExecutable(bufnr(''))
+
+Execute(use-global should override other versions):
+  let g:ale_swift_swiftlint_use_global = 1
+  call ale#test#SetFilename('swiftlint-test-files/cocoapods-and-react-native/testfile.swift')
+
+  AssertEqual
+  \ 'swiftlint_d',
+  \ ale_linters#swift#swiftlint#GetExecutable(bufnr(''))