vim. add indent file

Adresses Bug 529.

contrib/vim/indent/ledger.vim

@@ -0,0 +1,46 @@
+" Vim filetype indent file
+" filetype: ledger
+" by Johann Klähn; Use according to the terms of the GPL>=2.
+" vim:ts=2:sw=2:sts=2:foldmethod=marker
+
+if exists("b:did_indent")
+  finish
+endif
+let b:did_indent = 1
+
+setl autoindent
+setl indentexpr=GetLedgerIndent()
+
+if exists("*GetLedgerIndent")
+  finish
+endif
+
+function GetLedgerIndent(...)
+  " You can pass in a line number when calling this function manually.
+  let lnum = a:0 > 0 ? a:1 : v:lnum
+  " If this line is empty look at (the indentation of) the last line.
+  " Note that inside of a transaction no blank lines are allowed.
+  let line = getline(lnum)
+  let prev = getline(lnum - 1)
+
+  if line =~ '^\s\+\S'
+    " Lines that already are indented (→postings, sub-directives) keep their indentation.
+    return &sw
+  elseif line =~ '^\s*$'
+    " Current line is empty, try to guess its type based on the previous line.
+    if prev =~ '^\([[:digit:]~=]\|\s\+\S\)'
+      " This is very likely a posting or a sub-directive.
+      " While lines following the start of a transaction are automatically
+      " indented you will have to indent the first line following a
+      " pre-declaration manually. This makes it easier to type long lists of
+      " 'account' pre-declarations without sub-directives, for example.
+      return &sw
+    else
+      return 0
+    endif
+  else
+    " Everything else is not indented:
+    " start of transactions, pre-declarations, apply/end-lines
+    return 0
+  endif
+endf