feat: add g_ motion (move to last non-blank character)

Implements the g_ motion from vim, which moves to the last
non-whitespace character on the line. Supports counts (e.g. 2g_
moves to the last non-blank of the next line) and works correctly
with operators (dg_ deletes to last non-blank, preserving trailing
whitespace).

Author: legalcodes

src/vim.js

@@ -138,6 +138,7 @@ export function initVim(CM) {
     { keys: "g$", type: "motion", motion: "moveToEndOfDisplayLine" },
     { keys: "g^", type: "motion", motion: "moveToStartOfDisplayLine" },
     { keys: "g0", type: "motion", motion: "moveToStartOfDisplayLine" },
+    { keys: "g_", type: "motion", motion: "moveToLastNonWhiteSpaceCharacter", motionArgs: { inclusive: true }},
     { keys: '0', type: 'motion', motion: 'moveToStartOfLine' },
     { keys: '^', type: 'motion', motion: 'moveToFirstNonWhiteSpaceCharacter' },
     { keys: '+', type: 'motion', motion: 'moveByLines', motionArgs: { forward: true, toFirstChar:true }},
@@ -2537,6 +2538,12 @@ export function initVim(CM) {
       return new Pos(cursor.line,
                   findFirstNonWhiteSpaceCharacter(cm.getLine(cursor.line)));
     },
+    moveToLastNonWhiteSpaceCharacter: function(cm, head, motionArgs) {
+      var line = head.line + motionArgs.repeat - 1;
+      var lineText = cm.getLine(line);
+      var lastNonWS = findLastNonWhiteSpaceCharacter(lineText);
+      return new Pos(line, Math.max(0, lastNonWS));
+    },
     moveToMatchedSymbol: function(cm, head) {
       var cursor = head;
       var line = cursor.line;
@@ -4018,6 +4025,15 @@ export function initVim(CM) {
     return firstNonWS == -1 ? text.length : firstNonWS;
   }
 
+  /** @arg {string} [text] */
+  function findLastNonWhiteSpaceCharacter(text) {
+    if (!text) {
+      return 0;
+    }
+    var index = text.search(/\s+$/);
+    return index == -1 ? text.length - 1 : index - 1;
+  }
+
   /** 
    * @arg {CodeMirror} cm 
    * @arg {{inclusive?: boolean, innerWord?: boolean, bigWord?: boolean, noSymbol?: boolean, multiline?: boolean}} options

test/vim_test.js

@@ -541,6 +541,24 @@ testVim('g0_g$', function(cm, vim, helpers) {
   is(!/\.$/.test(cm.getValue()));
 
 },{ lineNumbers: false, lineWrapping:true, value: 'This line is long to test movement of g$ and g0 over wrapped lines.' });
+testVim('g_', function(cm, vim, helpers) {
+  // Test basic g_ on line with trailing spaces
+  cm.setCursor(0, 0);
+  helpers.doKeys('g', '_');
+  helpers.assertCursorAt(0, 2);
+  // Test g_ on line without trailing spaces
+  cm.setCursor(1, 0);
+  helpers.doKeys('g', '_');
+  helpers.assertCursorAt(1, 2);
+  // Test g_ with count (2g_ goes to last non-whitespace of next line)
+  cm.setCursor(0, 0);
+  helpers.doKeys('2', 'g', '_');
+  helpers.assertCursorAt(1, 2);
+  // Test dg_ deletes to last non-whitespace (preserving trailing spaces)
+  cm.setCursor(0, 0);
+  helpers.doKeys('d', 'g', '_');
+  eq('   \nfoo', cm.getValue());
+}, { value: 'foo   \nfoo' });
 testVim('}', function(cm, vim, helpers) {
   cm.setCursor(0, 0);
   helpers.doKeys('}');