patch 8.1.0496: no tests for indent files

Problem:    No tests for indent files.
Solution:   Add a mechanism for running indent file tests.  Add a first test
            for Vim indenting.

runtime/indent/testdir/runtest.vim

@@ -0,0 +1,117 @@
+" Runs all the indent tests for which there is no .out file
+
+set nocp
+filetype indent on
+set nowrapscan
+
+au! SwapExists * call HandleSwapExists()
+func HandleSwapExists()
+  " Ignore finding a swap file for the test input and output, the user might be
+  " editing them and that's OK.
+  if expand('<afile>') =~ '.*\.\(in\|out\|fail\|ok\)'
+    let v:swapchoice = 'e'
+  endif
+endfunc
+
+for fname in glob('testdir/*.in', 1, 1)
+  let root = substitute(fname, '\.in', '', '')
+
+  " Execute the test if the .out file does not exist of when the .in file is
+  " newer.
+  let in_time = getftime(fname)
+  let out_time = getftime(root . '.out')
+  if out_time < 0 || in_time > out_time
+    call delete(root . '.fail')
+    call delete(root . '.out')
+
+    set sw& ts& filetype=
+    exe 'split ' . fname
+
+    let did_some = 0
+    let failed = 0
+    let end = 1
+    while 1
+      " Indent all the lines between "START_INDENT" and "END_INDENT"
+      exe end
+      let start = search('\<START_INDENT\>')
+      let end = search('\<END_INDENT\>')
+      if start <= 0 || end <= 0 || end <= start
+	if did_some == 0
+	  call append(0, 'ERROR: START_INDENT and/or END_INDENT not found')
+	  let failed = 1
+	endif
+	break
+      else
+	let did_some = 1
+
+	" Execute all commands marked with INDENT_EXE and find any pattern.
+	let lnum = start
+	let pattern = ''
+	let at = ''
+	while 1
+	  exe lnum + 1
+	  let lnum_exe = search('\<INDENT_EXE\>')
+	  exe lnum + 1
+	  let indent_at = search('\<INDENT_\(AT\|NEXT\|PREV\)\>')
+	  if lnum_exe > 0 && lnum_exe < end && (indent_at <= 0 || lnum_exe < indent_at)
+	    exe substitute(getline(lnum_exe), '.*INDENT_EXE', '', '')
+	    let lnum = lnum_exe
+	    let start = lnum
+	  elseif indent_at > 0 && indent_at < end
+	    if pattern != ''
+	      call append(indent_at, 'ERROR: duplicate pattern')
+	      let failed = 1
+	      break
+	    endif
+	    let text = getline(indent_at)
+	    let pattern = substitute(text, '.*INDENT_\S*\s*', '', '')
+	    let at = substitute(text, '.*INDENT_\(\S*\).*', '\1', '')
+	    let lnum = indent_at
+	    let start = lnum
+	  else
+	    break
+	  endif
+	endwhile
+
+	exe start + 1
+	if pattern == ''
+	  exe 'normal =' . (end - 1) . 'G'
+	else
+	  let lnum = search(pattern)
+	  if lnum <= 0
+	    call append(indent_at, 'ERROR: pattern not found: ' . pattern)
+	    let failed = 1
+	    break
+	  endif
+	  if at == 'AT'
+	    exe lnum
+	  elseif at == 'NEXT'
+	    exe lnum + 1
+	  else
+	    exe lnum - 1
+	  endif
+	  normal ==
+	endif
+      endif
+    endwhile
+
+    if !failed
+      " Check the resulting text equals the .ok file.
+      if getline(1, '$') != readfile(root . '.ok')
+	let failed = 1
+      endif
+    endif
+
+    if failed
+      exe 'write ' . root . '.fail'
+      echoerr 'Test ' . fname . ' FAILED!'
+      sleep 2
+    else
+      exe 'write ' . root . '.out'
+    endif
+
+    quit!  " close the indented file
+  endif
+endfor
+
+qall!