Fixes to code actions (cursor moving, tests, EOL/EOF corner cases) (#3478)

* code_action: Don't move cursor when change covers entire file
* code_action: Refactor/simplify ApplyChanges
* code_action: Fix EOL at EOF corner cases while performing no changes
* code_action: Fix column around EOL corner cases
* code_action: Handle positions out of bounds
* code_action: Add instructions for verifying corner case tests against vscode

4 files changed, 250 insertions, 48 deletions

diff --git a/autoload/ale/code_action.vim b/autoload/ale/code_action.vim
index 69d40933..be4a25da 100644
--- a/autoload/ale/code_action.vim
+++ b/autoload/ale/code_action.vim
@@ -71,6 +71,11 @@ function! ale#code_action#ApplyChanges(filename, changes, should_save) abort
 
     if l:buffer > 0
         let l:lines = getbufline(l:buffer, 1, '$')
+
+        " Add empty line if there's trailing newline, like readfile() does.
+        if getbufvar(l:buffer, '&eol')
+            let l:lines += ['']
+        endif
     else
         let l:lines = readfile(a:filename, 'b')
     endif
@@ -89,62 +94,82 @@ function! ale#code_action#ApplyChanges(filename, changes, should_save) abort
         let l:end_column = l:code_edit.end.offset
         let l:text = l:code_edit.newText
 
-        " Adjust the ends according to previous edits.
-        if l:end_line > len(l:lines)
-            let l:end_line_len = 0
-        else
-            let l:end_line_len = len(l:lines[l:end_line - 1])
-        endif
-
         let l:insertions = split(l:text, '\n', 1)
 
-        if l:line is 1
-            " Same logic as for column below. Vimscript's slice [:-1] will not
-            " be an empty list.
-            let l:start = []
-        else
-            let l:start = l:lines[: l:line - 2]
-        endif
+        " Fix invalid columns
+        let l:column = l:column > 0 ? l:column : 1
+        let l:end_column = l:end_column > 0 ? l:end_column : 1
 
-        " Special case when text must be added after new line
-        if l:column > len(l:lines[l:line - 1])
-            call extend(l:start, [l:lines[l:line - 1]])
-            let l:column = 1
+        " Clamp start to BOF
+        if l:line < 1
+            let [l:line, l:column] = [1, 1]
         endif
 
-        if l:column is 1
-            " We need to handle column 1 specially, because we can't slice an
-            " empty string ending on index 0.
-            let l:middle = [l:insertions[0]]
-        else
-            let l:middle = [l:lines[l:line - 1][: l:column - 2] . l:insertions[0]]
+        " Clamp start to EOF
+        if l:line > len(l:lines) || l:line == len(l:lines) && l:column > len(l:lines[-1]) + 1
+            let [l:line, l:column] = [len(l:lines), len(l:lines[-1]) + 1]
+        " Special case when start is after EOL
+        elseif l:line < len(l:lines) && l:column > len(l:lines[l:line - 1]) + 1
+            let [l:line, l:column] = [l:line + 1, 1]
         endif
 
-        call extend(l:middle, l:insertions[1:])
+        " Adjust end: clamp if invalid and/or adjust if we moved start
+        if l:end_line < l:line || l:end_line == l:line && l:end_column < l:column
+            let [l:end_line, l:end_column] = [l:line, l:column]
+        endif
 
-        if l:end_line <= len(l:lines)
-            " Only extend the last line if end_line is within the range of
-            " lines.
-            let l:middle[-1] .= l:lines[l:end_line - 1][l:end_column - 1 :]
+        " Clamp end to EOF
+        if l:end_line > len(l:lines) || l:end_line == len(l:lines) && l:end_column > len(l:lines[-1]) + 1
+            let [l:end_line, l:end_column] = [len(l:lines), len(l:lines[-1]) + 1]
+        " Special case when end is after EOL
+        elseif l:end_line < len(l:lines) && l:end_column > len(l:lines[l:end_line - 1]) + 1
+            let [l:end_line, l:end_column] = [l:end_line + 1, 1]
         endif
 
+        " Careful, [:-1] is not an empty list
+        let l:start = l:line is 1 ? [] : l:lines[: l:line - 2]
+        let l:middle = l:column is 1 ? [''] : [l:lines[l:line - 1][: l:column - 2]]
+
+        let l:middle[-1] .= l:insertions[0]
+        let l:middle     += l:insertions[1:]
+        let l:middle[-1] .= l:lines[l:end_line - 1][l:end_column - 1 :]
+
+        let l:end_line_len = len(l:lines[l:end_line - 1])
         let l:lines_before_change = len(l:lines)
         let l:lines = l:start + l:middle + l:lines[l:end_line :]
 
         let l:current_line_offset = len(l:lines) - l:lines_before_change
         let l:column_offset = len(l:middle[-1]) - l:end_line_len
 
-        let l:pos = s:UpdateCursor(l:pos,
-        \ [l:line, l:column],
-        \ [l:end_line, l:end_column],
-        \ [l:current_line_offset, l:column_offset])
+        " Keep cursor where it was (if outside of changes) or move it after
+        " the changed text (if inside), but don't touch it when the change
+        " spans the entire buffer, in which case we have no clue and it's
+        " better to not do anything.
+        if l:line isnot 1 || l:column isnot 1
+        \|| l:end_line < l:lines_before_change
+        \|| l:end_line == l:lines_before_change && l:end_column <= l:end_line_len
+            let l:pos = s:UpdateCursor(l:pos,
+            \ [l:line, l:column],
+            \ [l:end_line, l:end_column],
+            \ [l:current_line_offset, l:column_offset])
+        endif
     endfor
 
-    if l:lines[-1] is# ''
+    if l:buffer > 0
+        " Make sure ale#util#{Writefile,SetBufferContents} add trailing
+        " newline if and only if it should be added.
+        if l:lines[-1] is# '' && getbufvar(l:buffer, '&eol')
+            call remove(l:lines, -1)
+        else
+            call setbufvar(l:buffer, '&eol', 0)
+        endif
+    elseif exists('+fixeol') && &fixeol && l:lines[-1] is# ''
+        " Not in buffer, ale#util#Writefile can't check &eol and always adds
+        " newline if &fixeol: remove to prevent double trailing newline.
         call remove(l:lines, -1)
     endif
 
-    if a:should_save
+    if a:should_save || l:buffer < 0
         call ale#util#Writefile(l:buffer, l:lines, a:filename)
     else
         call ale#util#SetBufferContents(l:buffer, l:lines)
diff --git a/test/test_code_action.vader b/test/test_code_action.vader
index 7eabb759..c613222c 100644
--- a/test/test_code_action.vader
+++ b/test/test_code_action.vader
@@ -1,14 +1,7 @@
 Before:
   Save g:ale_enabled
-
   let g:ale_enabled = 0
 
-  " Enable fix end-of-line as tests below expect that
-  set fixeol
-
-  runtime autoload/ale/code_action.vim
-  runtime autoload/ale/util.vim
-
   let g:file1 = tempname()
   let g:file2 = tempname()
   let g:test = {}
@@ -42,8 +35,6 @@ Before:
   endfunction!
 
 After:
-  Restore
-
   " Close the extra buffers if we opened it.
   if bufnr(g:file1) != -1
     execute ':bp! | :bd! ' . bufnr(g:file1)
@@ -65,8 +56,7 @@ After:
   unlet! g:changes
   delfunction WriteFileAndEdit
 
-  runtime autoload/ale/code_action.vim
-  runtime autoload/ale/util.vim
+  Restore
 
 
 Execute(It should modify and save multiple files):
@@ -214,7 +204,6 @@ Execute(End of file can be modified):
   \)
 
   AssertEqual g:test.text + [
-  \  '',
   \  'type A: string',
   \  'type B: number',
   \  '',
@@ -364,6 +353,15 @@ Execute(Cursor will not move when changes happening on lines >= cursor, but afte
   AssertEqual '  value: number', getline('.')
   AssertEqual [2, 3], getpos('.')[1:2]
 
+Execute(Cursor will not move when change covers entire file):
+  call WriteFileAndEdit()
+  call setpos('.', [0, 2, 3, 0])
+  call ale#code_action#HandleCodeAction(
+  \ g:test.create_change(1, 1, len(g:test.text) + 1, 1,
+  \   join(g:test.text + ['x'], "\n")),
+  \ {'should_save': 1})
+  AssertEqual [2, 3], getpos('.')[1:2]
+
 Execute(It should just modify file when should_save is set to v:false):
   call WriteFileAndEdit()
   let g:test.change = g:test.create_change(1, 1, 1, 1, "import { writeFile } from 'fs';\n")
diff --git a/test/test_code_action_corner_cases.vader b/test/test_code_action_corner_cases.vader
new file mode 100644
index 00000000..c44cf0ea
--- /dev/null
+++ b/test/test_code_action_corner_cases.vader
@@ -0,0 +1,179 @@
+" Tests for various corner cases of applying code changes from LSP.
+"
+" These can be verified against the reference vscode implementation using the
+" following javascript program:
+"
+"   const { TextDocument } = require('vscode-languageserver-textdocument');
+"   const { TextEdit, Position, Range } = require('vscode-languageserver-types');
+"   function MkPos(line, offset) { return Position.create(line - 1, offset - 1); }
+"   function MkInsert(pos, newText) { return TextEdit.insert(pos, newText); }
+"   function MkDelete(start, end) { return TextEdit.del(Range.create(start, end)); }
+"   function TestChanges(s, es) {
+"     return TextDocument.applyEdits(TextDocument.create(null, null, null, s), es);
+"   }
+"
+"   const fs = require("fs");
+"   const assert = require('assert').strict;
+"   const testRegex = /(?<!vscode skip.*)AssertEqual\s+("[^"]*"),\s*TestChanges\(("[^"]*"),\s*(\[[^\]]*\])/g;
+"   const data = fs.readFileSync(0, "utf-8");
+"   const tests = data.matchAll(testRegex);
+"   for (const test of tests) {
+"     console.log(test[0]);
+"     assert.equal(eval(test[1]), TestChanges(eval(test[2]), eval(test[3])));
+"   }
+"
+" Save it to test_code_action_corner_cases.js and invoke it using:
+"
+"   $ npm install vscode-languageserver-{textdocument,types}
+"   $ node test_code_action_corner_cases.js <test_code_action_corner_cases.vader
+
+Before:
+  Save &fixeol
+  set nofixeol
+
+  Save &fileformats
+  set fileformats=unix
+
+  " two files, one accessed through a buffer, the other using write/readfile only
+  let g:files = [tempname(), tempname()]
+
+  function! TestChanges(contents, changes, mode) abort
+    let l:file = g:files[a:mode is 'file' ? 0 : 1]
+    call writefile(split(a:contents, '\n', 1), l:file, 'bS')
+    if a:mode isnot 'file'
+      execute 'edit ' . l:file
+    endif
+    call ale#code_action#ApplyChanges(l:file, a:changes, a:mode isnot 'buffer')
+    if a:mode is 'buffer'
+      execute 'write ' . l:file
+    endif
+    return join(readfile(l:file, 'b'), "\n")
+  endfunction!
+
+  function! MkPos(line, offset) abort
+    return {'line': a:line, 'offset': a:offset}
+  endfunction!
+
+  function! MkInsert(pos, newText) abort
+    return {'start': a:pos, 'end': a:pos, 'newText': a:newText}
+  endfunction!
+
+  function! MkDelete(start, end) abort
+    return {'start': a:start, 'end': a:end, 'newText': ''}
+  endfunction!
+
+After:
+  for g:file in g:files
+    if bufnr(g:file) != -1
+      execute ':bp! | :bd! ' . bufnr(g:file)
+    endif
+    if filereadable(g:file)
+      call delete(g:file)
+    endif
+  endfor
+  unlet! g:files g:file
+
+  unlet! g:mode
+
+  delfunction TestChanges
+  delfunction MkPos
+  delfunction MkInsert
+  delfunction MkDelete
+
+  Restore
+
+Execute(Preserve (no)eol at eof):
+  for g:mode in ['save', 'file', 'buffer']
+    Log g:mode
+    AssertEqual "noeol",    TestChanges("noeol",    [], g:mode)
+    AssertEqual "eol\n",    TestChanges("eol\n",    [], g:mode)
+    AssertEqual "eols\n\n", TestChanges("eols\n\n", [], g:mode)
+  endfor
+
+  " there doesn't seem to be a way to tell if a buffer is empty or contains one
+  " empty line :-(
+  AssertEqual "", TestChanges("", [], 'file')
+
+Execute(Respect fixeol):
+  set fixeol
+  for g:mode in ['save', 'file', 'buffer']
+    Log g:mode
+    silent echo "vscode skip" | AssertEqual "noeol\n", TestChanges("noeol", [], g:mode)
+    silent echo "vscode skip" | AssertEqual "eol\n",   TestChanges("eol\n", [], g:mode)
+  endfor
+
+Execute(Add/del eol at eof):
+  for g:mode in ['save', 'file', 'buffer']
+    Log g:mode
+    AssertEqual "addeol\n", TestChanges("addeol",   [MkInsert(MkPos(1, 7), "\n")], g:mode)
+    AssertEqual "deleol",   TestChanges("deleol\n", [MkDelete(MkPos(1, 7), MkPos(1, 8))], g:mode)
+  endfor
+
+Execute(One character insertions to first line):
+  for g:mode in ['save', 'file', 'buffer']
+    Log g:mode
+    AssertEqual "xabc\ndef1\nghi\n", TestChanges("abc\ndef1\nghi\n", [MkInsert(MkPos(1, 0), "x")], g:mode)
+    AssertEqual "xabc\ndef2\nghi\n", TestChanges("abc\ndef2\nghi\n", [MkInsert(MkPos(1, 1), "x")], g:mode)
+    AssertEqual "axbc\ndef3\nghi\n", TestChanges("abc\ndef3\nghi\n", [MkInsert(MkPos(1, 2), "x")], g:mode)
+    AssertEqual "abcx\ndef4\nghi\n", TestChanges("abc\ndef4\nghi\n", [MkInsert(MkPos(1, 4), "x")], g:mode)
+    AssertEqual "abc\nxdef5\nghi\n", TestChanges("abc\ndef5\nghi\n", [MkInsert(MkPos(1, 5), "x")], g:mode)
+    AssertEqual "abc\nxdef6\nghi\n", TestChanges("abc\ndef6\nghi\n", [MkInsert(MkPos(1, 6), "x")], g:mode)
+  endfor
+
+Execute(One character + newline insertions to first line):
+  for g:mode in ['save', 'file', 'buffer']
+    Log g:mode
+    AssertEqual "x\nabc\ndef1\nghi\n", TestChanges("abc\ndef1\nghi\n", [MkInsert(MkPos(1, 0), "x\n")], g:mode)
+    AssertEqual "x\nabc\ndef2\nghi\n", TestChanges("abc\ndef2\nghi\n", [MkInsert(MkPos(1, 1), "x\n")], g:mode)
+    AssertEqual "ax\nbc\ndef3\nghi\n", TestChanges("abc\ndef3\nghi\n", [MkInsert(MkPos(1, 2), "x\n")], g:mode)
+    AssertEqual "abcx\n\ndef4\nghi\n", TestChanges("abc\ndef4\nghi\n", [MkInsert(MkPos(1, 4), "x\n")], g:mode)
+    AssertEqual "abc\nx\ndef5\nghi\n", TestChanges("abc\ndef5\nghi\n", [MkInsert(MkPos(1, 5), "x\n")], g:mode)
+    AssertEqual "abc\nx\ndef6\nghi\n", TestChanges("abc\ndef6\nghi\n", [MkInsert(MkPos(1, 6), "x\n")], g:mode)
+  endfor
+
+Execute(One character insertions near end):
+  for g:mode in ['save', 'file', 'buffer']
+    Log g:mode
+    AssertEqual "abc\ndef1\nghxi\n", TestChanges("abc\ndef1\nghi\n", [MkInsert(MkPos(3, 3), "x")], g:mode)
+    AssertEqual "abc\ndef2\nghix\n", TestChanges("abc\ndef2\nghi\n", [MkInsert(MkPos(3, 4), "x")], g:mode)
+    AssertEqual "abc\ndef3\nghi\nx", TestChanges("abc\ndef3\nghi\n", [MkInsert(MkPos(3, 5), "x")], g:mode)
+    AssertEqual "abc\ndef4\nghi\nx", TestChanges("abc\ndef4\nghi\n", [MkInsert(MkPos(3, 6), "x")], g:mode)
+    AssertEqual "abc\ndef5\nghi\nx", TestChanges("abc\ndef5\nghi\n", [MkInsert(MkPos(4, 1), "x")], g:mode)
+    AssertEqual "abc\ndef6\nghi\nx", TestChanges("abc\ndef6\nghi\n", [MkInsert(MkPos(4, 2), "x")], g:mode)
+    AssertEqual "abc\ndef7\nghi\nx", TestChanges("abc\ndef7\nghi\n", [MkInsert(MkPos(5, 1), "x")], g:mode)
+    AssertEqual "abc\ndef8\nghi\nx", TestChanges("abc\ndef8\nghi\n", [MkInsert(MkPos(5, 2), "x")], g:mode)
+  endfor
+
+Execute(One character + newline insertions near end):
+  for g:mode in ['save', 'file', 'buffer']
+    Log g:mode
+    AssertEqual "abc\ndef1\nghx\ni\n", TestChanges("abc\ndef1\nghi\n", [MkInsert(MkPos(3, 3), "x\n")], g:mode)
+    AssertEqual "abc\ndef2\nghix\n\n", TestChanges("abc\ndef2\nghi\n", [MkInsert(MkPos(3, 4), "x\n")], g:mode)
+    AssertEqual "abc\ndef3\nghi\nx\n", TestChanges("abc\ndef3\nghi\n", [MkInsert(MkPos(3, 5), "x\n")], g:mode)
+    AssertEqual "abc\ndef4\nghi\nx\n", TestChanges("abc\ndef4\nghi\n", [MkInsert(MkPos(3, 6), "x\n")], g:mode)
+    AssertEqual "abc\ndef5\nghi\nx\n", TestChanges("abc\ndef5\nghi\n", [MkInsert(MkPos(4, 1), "x\n")], g:mode)
+    AssertEqual "abc\ndef6\nghi\nx\n", TestChanges("abc\ndef6\nghi\n", [MkInsert(MkPos(4, 2), "x\n")], g:mode)
+  endfor
+
+Execute(Newline insertions near end):
+  for g:mode in ['save', 'file', 'buffer']
+    Log g:mode
+    AssertEqual "abc\ndef1\ngh\ni\n", TestChanges("abc\ndef1\nghi\n", [MkInsert(MkPos(3, 3), "\n")], g:mode)
+    AssertEqual "abc\ndef2\nghi\n\n", TestChanges("abc\ndef2\nghi\n", [MkInsert(MkPos(3, 4), "\n")], g:mode)
+    AssertEqual "abc\ndef3\nghi\n\n", TestChanges("abc\ndef3\nghi\n", [MkInsert(MkPos(3, 5), "\n")], g:mode)
+    AssertEqual "abc\ndef4\nghi\n\n", TestChanges("abc\ndef4\nghi\n", [MkInsert(MkPos(3, 6), "\n")], g:mode)
+    AssertEqual "abc\ndef5\nghi\n\n", TestChanges("abc\ndef5\nghi\n", [MkInsert(MkPos(4, 1), "\n")], g:mode)
+  endfor
+
+Execute(Single char deletions):
+  for g:mode in ['save', 'file', 'buffer']
+    Log g:mode
+    AssertEqual "bc\ndef1\nghi\n",  TestChanges("abc\ndef1\nghi\n", [MkDelete(MkPos(1, 1), MkPos(1, 2))], g:mode)
+    AssertEqual "ab\ndef2\nghi\n",  TestChanges("abc\ndef2\nghi\n", [MkDelete(MkPos(1, 3), MkPos(1, 4))], g:mode)
+    AssertEqual "abcdef3\nghi\n",   TestChanges("abc\ndef3\nghi\n", [MkDelete(MkPos(1, 4), MkPos(1, 5))], g:mode)
+    AssertEqual "abcdef4\nghi\n",   TestChanges("abc\ndef4\nghi\n", [MkDelete(MkPos(1, 4), MkPos(1, 6))], g:mode)
+    AssertEqual "abc\ndef5\ngh\n",  TestChanges("abc\ndef5\nghi\n", [MkDelete(MkPos(3, 3), MkPos(3, 4))], g:mode)
+    AssertEqual "abc\ndef6\nghi",   TestChanges("abc\ndef6\nghi\n", [MkDelete(MkPos(3, 4), MkPos(3, 5))], g:mode)
+    AssertEqual "abc\ndef7\nghi",   TestChanges("abc\ndef7\nghi\n", [MkDelete(MkPos(3, 4), MkPos(3, 6))], g:mode)
+    AssertEqual "abc\ndef8\nghi\n", TestChanges("abc\ndef8\nghi\n", [MkDelete(MkPos(4, 1), MkPos(4, 2))], g:mode)
+  endfor
diff --git a/test/test_code_action_python.vader b/test/test_code_action_python.vader
index fd30633d..2aac1ec7 100644
--- a/test/test_code_action_python.vader
+++ b/test/test_code_action_python.vader
@@ -35,7 +35,7 @@ Given python(Second python example):
 
 Execute():
   let g:changes = [
-  \ {'end': {'offset': 16, 'line': 2}, 'newText': "\n\ndef func_ivlpdpao(f):\n    exif = exifread.process_file(f)\n    dt = str(exif['Image DateTime'])\n    date = dt[:10].replace(':', '-')\n    return date\n", 'start': {'offset': 16, 'line': 2}},
+  \ {'end': {'offset': 16, 'line': 2}, 'newText': "\n\n\ndef func_ivlpdpao(f):\n    exif = exifread.process_file(f)\n    dt = str(exif['Image DateTime'])\n    date = dt[:10].replace(':', '-')\n    return date\n", 'start': {'offset': 16, 'line': 2}},
   \ {'end': {'offset': 32, 'line': 6}, 'newText': 'date = func', 'start': {'offset': 9, 'line': 6}},
   \ {'end': {'offset': 42, 'line': 8}, 'newText': "ivlpdpao(f)\n", 'start': {'offset': 33, 'line': 6}}
   \]