Fix #1727 - Replace previoulsy defined linters with matching names

autoload/ale/linter.vim

@@ -358,12 +358,14 @@ function! ale#linter#Define(filetype, linter) abort
     " This command will throw from the sandbox.
     let &l:equalprg=&l:equalprg
 
+    let l:new_linter = ale#linter#PreProcess(a:filetype, a:linter)
+
     if !has_key(s:linters, a:filetype)
         let s:linters[a:filetype] = []
     endif
 
-    let l:new_linter = ale#linter#PreProcess(a:filetype, a:linter)
-
+    " Remove previously defined linters with the same name.
+    call filter(s:linters[a:filetype], 'v:val.name isnot# a:linter.name')
     call add(s:linters[a:filetype], l:new_linter)
 endfunction
 

test/test_linter_retrieval.vader

@@ -158,6 +158,14 @@ Execute (Buffer-local overrides for aliases should be used):
 
   AssertEqual [g:testlinter1, g:testlinter2], ale#linter#Get('testft1')
 
+Execute (Linters new linters with the same name should replace old ones):
+  let g:testlinter1.name = g:testlinter2.name
+
+  call ale#linter#Define('testft1', g:testlinter1)
+  call ale#linter#Define('testft1', g:testlinter2)
+
+  AssertEqual [g:testlinter2], ale#linter#GetAll(['testft1'])
+
 Execute (Linters should be loaded from disk appropriately):
   call ale#linter#Reset()
   AssertEqual [{'name': 'testlinter', 'output_stream': 'stdout', 'executable': 'testlinter', 'command': 'testlinter', 'callback': 'testCB', 'read_buffer': 1, 'lint_file': 0, 'aliases': [], 'lsp': ''}], ale#linter#Get('testft')