'inccommand': fix 'gdefault' lockup #7261

closes #7244
ref #7249

src/nvim/ex_cmds.c

@@ -3665,9 +3665,38 @@ static buf_T *do_sub(exarg_T *eap, proftime_T timeout)
          * use "\=col("."). */
         curwin->w_cursor.col = regmatch.startpos[0].col;
 
+        // When the match included the "$" of the last line it may
+        // go beyond the last line of the buffer.
+        if (nmatch > curbuf->b_ml.ml_line_count - sub_firstlnum + 1) {
+          nmatch = curbuf->b_ml.ml_line_count - sub_firstlnum + 1;
+          skip_match = true;
+        }
+
         // 3. Substitute the string. During 'inccommand' preview only do this if
         //    there is a replace pattern.
-        if (!preview || has_second_delim) {
+        if (preview && !has_second_delim) {
+          // For a multi-line match, make a copy of the last matched
+          // line and continue in that one.
+          if (nmatch > 1) {
+            sub_firstlnum += nmatch - 1;
+            xfree(sub_firstline);
+            sub_firstline = vim_strsave(ml_get(sub_firstlnum));
+            // When going beyond the last line, stop substituting.
+            if (sub_firstlnum <= line2) {
+              do_again = true;
+            } else {
+              subflags.do_all = false;
+            }
+          }
+
+          if (skip_match) {
+            // Already hit end of the buffer, sub_firstlnum is one
+            // less than what it ought to be.
+            xfree(sub_firstline);
+            sub_firstline = vim_strsave((char_u *)"");
+            copycol = 0;
+          }
+        } else if (!preview || has_second_delim) {
           if (subflags.do_count) {
             // prevent accidentally changing the buffer by a function
             save_ma = curbuf->b_p_ma;
@@ -3691,13 +3720,6 @@ static buf_T *do_sub(exarg_T *eap, proftime_T timeout)
             goto skip;
           }
 
-          // When the match included the "$" of the last line it may
-          // go beyond the last line of the buffer.
-          if (nmatch > curbuf->b_ml.ml_line_count - sub_firstlnum + 1) {
-            nmatch = curbuf->b_ml.ml_line_count - sub_firstlnum + 1;
-            skip_match = true;
-          }
-
           // Need room for:
           // - result so far in new_start (not for first sub in line)
           // - original text up to match

test/functional/ui/inccommand_spec.lua

@@ -14,6 +14,7 @@ local neq = helpers.neq
 local ok = helpers.ok
 local source = helpers.source
 local wait = helpers.wait
+local nvim = helpers.nvim
 
 local default_text = [[
   Inc substitution on
@@ -1647,3 +1648,29 @@ describe("'inccommand' split windows", function()
   end)
 
 end)
+
+describe("'inccommand' with 'gdefault'", function()
+  before_each(function()
+    clear()
+  end)
+
+  it("does not lock up #7244", function()
+    common_setup(nil, "nosplit", "{")
+    command("set gdefault")
+    feed(":s/{\\n")
+    eq({mode='c', blocking=false}, nvim("get_mode"))
+    feed("/A<Enter>")
+    expect("A")
+    eq({mode='n', blocking=false}, nvim("get_mode"))
+  end)
+
+  it("with multiline text and range, does not lock up #7244", function()
+    common_setup(nil, "nosplit", "{\n\n{")
+    command("set gdefault")
+    feed(":%s/{\\n")
+    eq({mode='c', blocking=false}, nvim("get_mode"))
+    feed("/A<Enter>")
+    expect("A\nA")
+    eq({mode='n', blocking=false}, nvim("get_mode"))
+  end)
+end)