patch 9.0.1036: undo misbehaves when writing from an insert mode mappingv9.0.1036

Problem:    Undo misbehaves when writing from an insert mode mapping.
Solution:   Sync undo when writing. (closes #11674)

3 files changed, 14 insertions, 0 deletions

diff --git a/src/testdir/dumps/Test_undo_after_write_1.dump b/src/testdir/dumps/Test_undo_after_write_1.dump
new file mode 100644
index 0000000000..92410d446b
--- /dev/null
+++ b/src/testdir/dumps/Test_undo_after_write_1.dump
@@ -0,0 +1,6 @@
+|t+0&#ffffff0|e|s>t| @70
+@75
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|1+0#0000000&| |l|i|n|e| |l|e|s@1|;| |b|e|f|o|r|e| |#|2| @1|0| |s|e|c|o|n|d|s| |a|g|o| @19|1|,|4| @10|A|l@1| 
diff --git a/src/testdir/dumps/Test_undo_after_write_2.dump b/src/testdir/dumps/Test_undo_after_write_2.dump
new file mode 100644
index 0000000000..029e3243ed
--- /dev/null
+++ b/src/testdir/dumps/Test_undo_after_write_2.dump
@@ -0,0 +1,6 @@
+> +0&#ffffff0@74
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|2+0#0000000&| |f|e|w|e|r| |l|i|n|e|s|;| |b|e|f|o|r|e| |#|1| @1|1| |s|e|c|o|n|d| |a|g|o| @18|0|,|0|-|1| @8|A|l@1| 
diff --git a/src/testdir/dumps/Test_undo_after_write_2.vim b/src/testdir/dumps/Test_undo_after_write_2.vim
new file mode 100644
index 0000000000..d1d3c3d48d
--- /dev/null
+++ b/src/testdir/dumps/Test_undo_after_write_2.vim
@@ -0,0 +1,2 @@
+" Filter that changes the "1 second ago" message to "0 seconds ago".
+6s+|1| |s|e|c|o|n|d| |a|g|o| @18|+|0| |s|e|c|o|n|d|s| |a|g|o| @17|+e