fix(shada): don't store empty replacement string

src/nvim/shada.c

@@ -2417,19 +2417,21 @@ static ShaDaWriteResult shada_write(FileDescriptor *const sd_writer,
     // Initialize substitute replacement string
     SubReplacementString sub;
     sub_get_replacement(&sub);
-    wms->replacement = (PossiblyFreedShadaEntry) {
-      .can_free_entry = false,
-      .data = {
-        .type = kSDItemSubString,
-        .timestamp = sub.timestamp,
+    if (sub.sub != NULL) {  // Don't store empty replacement string
+      wms->replacement = (PossiblyFreedShadaEntry) {
+        .can_free_entry = false,
         .data = {
-          .sub_string = {
-            .sub = sub.sub,
-          }
-        },
-        .additional_data = sub.additional_data,
-      }
-    };
+          .type = kSDItemSubString,
+          .timestamp = sub.timestamp,
+          .data = {
+            .sub_string = {
+              .sub = sub.sub,
+            }
+          },
+          .additional_data = sub.additional_data,
+        }
+      };
+    }
   }
 
   // Initialize global marks

test/functional/shada/history_spec.lua

@@ -239,9 +239,10 @@ describe('ShaDa support code', function()
     nvim_command('silent! /«/')
     expect_exit(nvim_command, 'qall!')
     reset()
-    fn.setline('.', { '\171«' })
-    nvim_command('~&')
-    eq('\171', fn.getline('.'))
+    fn.setline('.', { 'foo', '\171«' })
+    nvim_feed('gg0n')
+    eq({ 0, 2, 2, 0 }, fn.getpos('.'))
+    eq('\171«', fn.getline('.'))
     eq('', fn.histget('/', -1))
   end)
 
@@ -250,9 +251,10 @@ describe('ShaDa support code', function()
     nvim_command('silent! /\171/')
     expect_exit(nvim_command, 'qall!')
     reset()
-    fn.setline('.', { '\171«' })
-    nvim_command('~&')
-    eq('«', fn.getline('.'))
+    fn.setline('.', { 'foo', '\171«' })
+    nvim_feed('gg0n')
+    eq({ 0, 2, 1, 0 }, fn.getpos('.'))
+    eq('\171«', fn.getline('.'))
     eq('', fn.histget('/', -1))
   end)
 
@@ -277,4 +279,14 @@ describe('ShaDa support code', function()
     nvim_command('wshada')
     assert_alive()
   end)
+
+  it('does not dump empty replacement string', function()
+    expect_exit(nvim_command, 'qall!')
+    reset()
+    fn.setline('.', { 'foo', 'bar' })
+    nvim_command('language C')
+    nvim_feed('/f\n')
+    local err = pcall_err(nvim_command, '~&')
+    eq('Vim(~):E33: No previous substitute regular expression', err)
+  end)
 end)