patch 8.1.0295: no 'incsearch' highlighting for :vimgrep and similar

Problem:    No 'incsearch' highlighting for :vimgrep and similar commands.
Solution:   Parse the :vimgrep command and similar ones to locate the search
            pattern. (Hirohito Higashi, closes #3344)
diff --git a/src/testdir/dumps/Test_incsearch_vimgrep_01.dump b/src/testdir/dumps/Test_incsearch_vimgrep_01.dump
new file mode 100644
index 0000000..955d030
--- /dev/null
+++ b/src/testdir/dumps/Test_incsearch_vimgrep_01.dump
@@ -0,0 +1,9 @@
+|a+0&#ffffff0|n|o|t|h|e|r| |o+1&&|n|e+0&&| |2| @56
+|t|h|a|t| |o+0&#ffff4012|n|e+0&#ffffff0| |3| @59
+|t|h|e| |o+0&#ffff4012|n|e+0&#ffffff0| |1| @60
+|~+0#4040ff13&| @68
+|~| @68
+|~| @68
+|~| @68
+|~| @68
+|:+0#0000000&|v|i|m|g|r|e|p| |o|n> @58
diff --git a/src/testdir/dumps/Test_incsearch_vimgrep_02.dump b/src/testdir/dumps/Test_incsearch_vimgrep_02.dump
new file mode 100644
index 0000000..a5d94ea
--- /dev/null
+++ b/src/testdir/dumps/Test_incsearch_vimgrep_02.dump
@@ -0,0 +1,9 @@
+|a+0&#ffffff0|n|o|t|h|e|r| |o+1&&|n|e+0&&| |2| @56
+|t|h|a|t| |o+0&#ffff4012|n|e+0&#ffffff0| |3| @59
+|t|h|e| |o+0&#ffff4012|n|e+0&#ffffff0| |1| @60
+|~+0#4040ff13&| @68
+|~| @68
+|~| @68
+|~| @68
+|~| @68
+|:+0#0000000&|v|i|m|g| |/|o|n|/| |*|.|t|x|t> @53
diff --git a/src/testdir/dumps/Test_incsearch_vimgrep_03.dump b/src/testdir/dumps/Test_incsearch_vimgrep_03.dump
new file mode 100644
index 0000000..038ceb9
--- /dev/null
+++ b/src/testdir/dumps/Test_incsearch_vimgrep_03.dump
@@ -0,0 +1,9 @@
+|a+0&#ffffff0|n|o|t|h|e|r| |o+1&&|n|e+0&&| |2| @56
+|t|h|a|t| |o+0&#ffff4012|n|e+0&#ffffff0| |3| @59
+|t|h|e| |o+0&#ffff4012|n|e+0&#ffffff0| |1| @60
+|~+0#4040ff13&| @68
+|~| @68
+|~| @68
+|~| @68
+|~| @68
+|:+0#0000000&|v|i|m|g|r|e|p|a|d@1| |"|\|<|o|n> @52
diff --git a/src/testdir/dumps/Test_incsearch_vimgrep_04.dump b/src/testdir/dumps/Test_incsearch_vimgrep_04.dump
new file mode 100644
index 0000000..92dd78d
--- /dev/null
+++ b/src/testdir/dumps/Test_incsearch_vimgrep_04.dump
@@ -0,0 +1,9 @@
+|a+0&#ffffff0|n|o|t|h|e|r| |o|n|e| |2| @56
+|t+1&&|h|a|t+0&&| |o|n|e| |3| @59
+|t|h|e| |o|n|e| |1| @60
+|~+0#4040ff13&| @68
+|~| @68
+|~| @68
+|~| @68
+|~| @68
+|:+0#0000000&|l|v| |"|t|h|a> @61
diff --git a/src/testdir/dumps/Test_incsearch_vimgrep_05.dump b/src/testdir/dumps/Test_incsearch_vimgrep_05.dump
new file mode 100644
index 0000000..e11ff57
--- /dev/null
+++ b/src/testdir/dumps/Test_incsearch_vimgrep_05.dump
@@ -0,0 +1,9 @@
+|a+0&#ffffff0|n|o|t+1&&|h|e|r+0&&| |o|n|e| |2| @56
+|t|h|a|t| |o|n|e| |3| @59
+|t+0&#ffff4012|h|e| +0&#ffffff0|o|n|e| |1| @60
+|~+0#4040ff13&| @68
+|~| @68
+|~| @68
+|~| @68
+|~| @68
+|:+0#0000000&|l|v|i|m|g|r|e|p|a| |"|t|h|e|"| |*@1|/|*|.|t|x|t> @44
diff --git a/src/testdir/test_search.vim b/src/testdir/test_search.vim
index da388cd..9ede26d 100644
--- a/src/testdir/test_search.vim
+++ b/src/testdir/test_search.vim
@@ -944,6 +944,53 @@
   call delete('Xis_sort_script')
 endfunc
 
+" Similar to Test_incsearch_substitute_dump() for :vimgrep famiry
+func Test_incsearch_vimgrep_dump()
+  if !exists('+incsearch')
+    return
+  endif
+  if !CanRunVimInTerminal()
+    return
+  endif
+  call writefile([
+	\ 'set incsearch hlsearch scrolloff=0',
+	\ 'call setline(1, ["another one 2", "that one 3", "the one 1"])',
+	\ ], 'Xis_vimgrep_script')
+  let buf = RunVimInTerminal('-S Xis_vimgrep_script', {'rows': 9, 'cols': 70})
+  " Give Vim a chance to redraw to get rid of the spaces in line 2 caused by
+  " the 'ambiwidth' check.
+  sleep 100m
+
+  " Need to send one key at a time to force a redraw.
+  call term_sendkeys(buf, ':vimgrep on')
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_incsearch_vimgrep_01', {})
+  call term_sendkeys(buf, "\<Esc>")
+
+  call term_sendkeys(buf, ':vimg /on/ *.txt')
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_incsearch_vimgrep_02', {})
+  call term_sendkeys(buf, "\<Esc>")
+
+  call term_sendkeys(buf, ':vimgrepadd "\<on')
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_incsearch_vimgrep_03', {})
+  call term_sendkeys(buf, "\<Esc>")
+
+  call term_sendkeys(buf, ':lv "tha')
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_incsearch_vimgrep_04', {})
+  call term_sendkeys(buf, "\<Esc>")
+
+  call term_sendkeys(buf, ':lvimgrepa "the" **/*.txt')
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_incsearch_vimgrep_05', {})
+  call term_sendkeys(buf, "\<Esc>")
+
+  call StopVimInTerminal(buf)
+  call delete('Xis_vimgrep_script')
+endfunc
+
 func Test_search_undefined_behaviour()
   if !has("terminal")
     return