improve the lsp diagnostic message format (#2425)

autoload/ale/lsp/response.vim

@@ -28,7 +28,7 @@ function! ale#lsp#response#ReadDiagnostics(response) abort
     for l:diagnostic in a:response.params.diagnostics
         let l:severity = get(l:diagnostic, 'severity', 0)
         let l:loclist_item = {
-        \   'text': l:diagnostic.message,
+        \   'text': substitute(l:diagnostic.message, '\(\r\n\|\n\|\r\)', ' ', 'g'),
         \   'type': 'E',
         \   'lnum': l:diagnostic.range.start.line + 1,
         \   'col': l:diagnostic.range.start.character + 1,

test/lsp/test_read_lsp_diagnostics.vader

@@ -109,6 +109,26 @@ Execute(ale#lsp#response#ReadDiagnostics() should include sources in detail):
   \   }
   \ ]}})
 
+Execute(ale#lsp#response#ReadDiagnostics() should keep detail with line breaks but replace with spaces in text):
+  AssertEqual [
+  \   {
+  \     'type': 'E',
+  \     'text': 'cannot borrow `cap` as mutable more than once at a time  mutable borrow starts here in previous iteration of loop',
+  \     'detail': "[rustc] cannot borrow `cap` as mutable\r\nmore than once at a time\n\nmutable borrow starts here\rin previous iteration of loop",
+  \     'lnum': 10,
+  \     'col': 15,
+  \     'end_lnum': 12,
+  \     'end_col': 22,
+  \   }
+  \ ],
+  \ ale#lsp#response#ReadDiagnostics({'params': {'uri': 'filename.ts', 'diagnostics': [
+  \   {
+  \     'range': Range(9, 14, 11, 22),
+  \     'message': "cannot borrow `cap` as mutable\r\nmore than once at a time\n\nmutable borrow starts here\rin previous iteration of loop",
+  \     'source': 'rustc',
+  \   }
+  \ ]}})
+
 Execute(ale#lsp#response#ReadDiagnostics() should consider -1 to be a meaningless code):
   AssertEqual [
   \   {