Fix #4714 - Handle ruff garbage

When ruff outputs errors are invalid JSON text, handle that and stop ALE
from throwing exceptions.

2 files changed, 61 insertions, 10 deletions

diff --git a/ale_linters/python/ruff.vim b/ale_linters/python/ruff.vim
index aa605ba5..f30d42c0 100644
--- a/ale_linters/python/ruff.vim
+++ b/ale_linters/python/ruff.vim
@@ -61,17 +61,25 @@ endfunction
 function! ale_linters#python#ruff#Handle(buffer, lines) abort
     let l:output = []
 
+    " Read all lines of ruff output and parse use all the valid JSONL lines.
     for l:line in a:lines
-        let l:item = json_decode(l:line)
-        call add(l:output, {
-        \   'lnum': l:item.location.row,
-        \   'col': l:item.location.column,
-        \   'end_lnum': l:item.end_location.row,
-        \   'end_col': l:item.end_location.column - 1,
-        \   'code': l:item.code,
-        \   'text': l:item.message,
-        \   'type': l:item.code =~? '\vE\d+' ? 'E' : 'W',
-        \})
+        try
+            let l:item = json_decode(l:line)
+        catch
+            let l:item = v:null
+        endtry
+
+        if !empty(l:item)
+            call add(l:output, {
+            \   'lnum': l:item.location.row,
+            \   'col': l:item.location.column,
+            \   'end_lnum': l:item.end_location.row,
+            \   'end_col': l:item.end_location.column - 1,
+            \   'code': l:item.code,
+            \   'text': l:item.message,
+            \   'type': l:item.code =~? '\vE\d+' ? 'E' : 'W',
+            \})
+        endif
     endfor
 
     return l:output
diff --git a/test/handler/test_ruff_handler.vader b/test/handler/test_ruff_handler.vader
new file mode 100644
index 00000000..82012706
--- /dev/null
+++ b/test/handler/test_ruff_handler.vader
@@ -0,0 +1,43 @@
+Before:
+  runtime ale_linters/python/ruff.vim
+
+After:
+  call ale#linter#Reset()
+
+Execute(We should handle basic output of ruff correctly):
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 2,
+  \     'col': 1,
+  \     'code': 'F821',
+  \     'type': 'W',
+  \     'end_col': 7,
+  \     'end_lnum': 2,
+  \     'text': 'Undefined name example',
+  \   },
+  \ ],
+  \ ale_linters#python#ruff#Handle(bufnr(''), [
+  \   '{"cell":null,"code":"F821","end_location":{"column":8,"row":2},"filename":"/home/eduardo/Code/Python/test.py","fix":null,"location":{"column":1,"row":2},"message":"Undefined name example","noqa_row":2,"url":"https://docs.astral.sh/ruff/rules/undefined-name"}',
+  \ ])
+
+Execute(We should handle totally broken output from ruff):
+  AssertEqual [], ale_linters#python#ruff#Handle(bufnr(''), ['ERROR: oh noes!'])
+
+Execute(We should handle mixed error lines and JSON output from ruff):
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 2,
+  \     'col': 1,
+  \     'code': 'F821',
+  \     'type': 'W',
+  \     'end_col': 7,
+  \     'end_lnum': 2,
+  \     'text': 'Undefined name example',
+  \   },
+  \ ],
+  \ ale_linters#python#ruff#Handle(bufnr(''), [
+  \   'ERROR: oh noes!',
+  \   '{"cell":null,"code":"F821","end_location":{"column":8,"row":2},"filename":"/home/eduardo/Code/Python/test.py","fix":null,"location":{"column":1,"row":2},"message":"Undefined name example","noqa_row":2,"url":"https://docs.astral.sh/ruff/rules/undefined-name"}',
+  \ ])