Named blocks standardization

1 Rationale
2 Existing implementations
3 Comparison of existing implementations
4 Problems

Rationale

Several lenses (logrotate.aug, xinetd.aug, keepalived.aug, aptconf.aug, dhclient.aug, shellvars.aug) use named blocks with the following syntax:

  block_name {
     entry+
  }

but each lens implements it differently. It would be good to add a (or several types of) block entry to build.aug to make it easier to build such blocks in a standard way.

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Existing implementations

The following are existing implementations of such blocks. They are not working examples, but they show the general pattern of each implementation.

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xinetd.aug

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Code

 let body (attr:lens) = del /\n\{[ \t]*\n/ "\n{\n"
                      . (empty|comment|attr)*
                      . del /[ \t]*\}[ \t]*\n/ "}\n"
  
 let service =
    let sto_re = /[^# \t\n\/]+/ in
    [ key "service" . Sep.space . store sto_re . body service_attr ]

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Notes

This implementation forces a newline after the opening bracket;

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logrotate.aug

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Code

  let body = del /\{[ \t]*\n/ "{\n"
                      . ( comment "\t" | attrs "\t" | hooks | empty )*
                      . del /[ \t]*\}[ \t]*\n/ "}\n"
  
  let rule =
    [ label "rule" . Util.indent .
        [ label "file" . store filename ] .
        [ del /[ \t\n]+/ " " . label "file" . store filename ]* .
        del /[ \t\n]*/ " " . body ]

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Notes

This lens was inspired by xinetd.aug and uses a similar "body" construct, only more complex;

This example shows that a standard block pattern should take a lens as the block name rather than a regexp, since the construction in logrotate.aug accepts several files (we could use Build.opt_list here) before the body;

This implementation forces a newline after the opening bracket, just like xinetd.aug;

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keepalived.aug

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Code

  let lbracket = Util.del_str "{"
  
  let rbracket = Util.del_str "}"
  
  let lens_block (title:lens) (sto:lens) = [ indent . title . opt_eol . lbracket
                                        . (sto | empty | comment)+
                                        . indent . rbracket . eol ]

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Notes

This lens doesn't force a newline after the opening bracket;

As a result, new blocks have no newlines;

This lens allows for eol before the opening bracket. This might not be the case of all formats (but it doesn't hurt in general to support it);

This lens doesn't allow the closing bracket to be on the same line as an entry (since entries have eol);

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aptconf.aug

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Code

 let rec entry_noeol =
  let value =
     Util.del_str "\"" . store /[^"\n]+/
                       . del /";?/ "\";" in
  let opt_eol = del /[ \t\n]*/ "\n" in
  let long_eol = del /[ \t]*\n+/ "\n" in
  let list_elem = [ opt_eol . label "@elem" . value ] in
  let eol_comment = del /([ \t\n]*\n)?/ "" . comment in
      [ key name_re . Sep.space . value ]
    | [ key name_re . del /[ \t\n]*\{/ " {" .
          ( (opt_eol . entry_noeol) |
            list_elem |
            eol_comment
            )* .
          del /[ \t\n]*\};?/ "\n};" ]
    | [ key name_re . Util.del_str "::" . entry_noeol ]
 
 let entry = indent . entry_noeol . eol

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