patch 8.0.1668: terminal debugger: can't re-open source code window

Problem:    Terminal debugger: can't re-open source code window.
Solution:   Add the :Source command.  Also create the window if needed when
            gdb stops at a source line.

runtime/doc/terminal.txt

@@ -731,6 +731,11 @@ to have the 'mouse' option set to enable mouse clicks.
 You can add the window toolbar in other windows you open with: >
   :Winbar
 
+If gdb stops at a source line and there is no window currently showing the
+source code, a new window will be created for the source code.  This also
+happens if the buffer in the source code window has been modified and can't be
+abandoned.
+
 
 Inspecting variables ~
 							*termdebug-variables*
@@ -747,6 +752,8 @@ Other commands ~
 							*termdebug-commands*
  :Gdb	     jump to the gdb window
  :Program    jump to the window with the running program
+ :Source     jump to the window with the source code, create it if there
+	     isn't one
 
 
 Communication ~

runtime/pack/dist/opt/termdebug/plugin/termdebug.vim

@@ -246,6 +246,7 @@ func s:InstallCommands()
   command -range -nargs=* Evaluate call s:Evaluate(<range>, <q-args>)
   command Gdb call win_gotoid(s:gdbwin)
   command Program call win_gotoid(s:ptywin)
+  command Source call s:GotoStartwinOrCreateIt()
   command Winbar call s:InstallWinbar()
 
   " TODO: can the K mapping be restored?
@@ -269,6 +270,7 @@ let s:winbar_winids = []
 
 " Install the window toolbar in the current window.
 func s:InstallWinbar()
+  if has('menu') && &mouse != ''
     nnoremenu WinBar.Step   :Step<CR>
     nnoremenu WinBar.Next   :Over<CR>
     nnoremenu WinBar.Finish :Finish<CR>
@@ -276,6 +278,7 @@ func s:InstallWinbar()
     nnoremenu WinBar.Stop   :Stop<CR>
     nnoremenu WinBar.Eval   :Evaluate<CR>
     call add(s:winbar_winids, win_getid(winnr()))
+  endif
 endfunc
 
 " Delete installed debugger commands in the current window.
@@ -450,6 +453,14 @@ func s:HandleError(msg)
   echoerr substitute(a:msg, '.*msg="\(.*\)"', '\1', '')
 endfunc
 
+func s:GotoStartwinOrCreateIt()
+  if !win_gotoid(s:startwin)
+    new
+    let s:startwin = win_getid(winnr())
+    call s:InstallWinbar()
+  endif
+endfunc
+
 " Handle stopping and running message from gdb.
 " Will update the sign that shows the current position.
 func s:HandleCursor(msg)
@@ -461,7 +472,8 @@ func s:HandleCursor(msg)
     let s:stopped = 0
   endif
 
-  if win_gotoid(s:startwin)
+  call s:GotoStartwinOrCreateIt()
+
   let fname = substitute(a:msg, '.*fullname="\([^"]*\)".*', '\1', '')
   if a:msg =~ '^\(\*stopped\|=thread-selected\)' && filereadable(fname)
     let lnum = substitute(a:msg, '.*line="\([^"]*\)".*', '\1', '')
@@ -471,6 +483,7 @@ func s:HandleCursor(msg)
 	  " TODO: find existing window
 	  exe 'split ' . fnameescape(fname)
 	  let s:startwin = win_getid(winnr())
+	  call s:InstallWinbar()
 	else
 	  exe 'edit ' . fnameescape(fname)
 	endif
@@ -485,7 +498,6 @@ func s:HandleCursor(msg)
   endif
 
   call win_gotoid(wid)
-  endif
 endfunc
 
 " Handle setting a breakpoint

src/version.c

@@ -762,6 +762,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1668,
 /**/
     1667,
 /**/