[augeas-devel] Lens Help: disambiguating 1] regex difference 2] overlapping lenses in union.put

[Yclept Nemo]

Hi,

I'm working on a lens that has two errors:

 >>  1 (*
 >>  2 # example configuration follows:
 >>  3 # default = value
 >>  4 key = value
 >>  5
 >>  6 # default = value # inline comment
 >>  7 key = value # inline comment
 >>  8 *)
 >>  9
 >> 10 (*
 >> 11 # key/value formats:
 >> 12
 >> 13 keys
 >> 14     [a-z_]
 >> 15
 >> 16 values
 >> 17     boolean:            true/false
 >> 18     int                 0, 100
 >> 19     real                3.0
 >> 20     hex int             ffeedd
 >> 21     string              "..."
 >> 22     unquoted string     sdl, f, f2
 >> 23 *)
 >> 24
 >> 25 (*
 >> 26 # quoted string regex scratchpad
 >> 27 quoted string regex =
 >> 28     good:
 >> 29         "asdf\"qwer"
 >> 30         "asdf\\qwer"
 >> 31         "asdf\\\\\"qwer"
 >> 32     bad:
 >> 33         "asdf\\"qwer"
 >> 34         "asdf\\\\\\"qwer"
 >> 35
 >> 36     /.*/ - /.*(\\)*[^\]".*/
 >> 37
 >> 38     /([^"](\")?)*/
 >> 39 *)
 >> 40
 >> 41 module ConfigObj =
 >> 42     let _               = print_regexp /"/
 >> 43     let _               = print_string "\n"
 >> 44     let var0            = "\""
 >> 45     let _               = print_string (var0 . "\n")
 >> 46     let _               = print_string "\n"
 >> 47
 >> 48     let var1            = "\"asdf\\\\\\\\"qwer\""
 >> 49     let _               = print_string (var1 . "\n")
 >> 50     let _               = print_string ((regexp_match (/\".*\"/ -
/\"(.*[^\])?([\]{2})*".*\"/) var1) . "\n")
 >> 51
 >> 52     let option          = key /[a-z]([a-z_]*[a-z])?/
 >> 53     let value_bool      = store /(true|false)/ . [ label "type" .
value "bool" ]
 >> 54     let value_int       = store /(0|[1-9][0-9]*)/ . [ label "type" .
value "int" ]
 >> 55     let value_decimal   = store ((lens_ctype value_int) .
/\.[0-9]+/) . [ label "type" . value "decimal" ]
 >> 56     let value_string    = (del "\"" "\"") . (store (/.*/ -
/(.*[^\]|)([\]{2})*".*/)) . (del "\"" "\"") . [ label "type" . value
"string" ]
 >> 57     let value_all       = value_bool | value_int | value_decimal
 >> 58     let sep_assign      = del /[ \t]*=[ \t]*/ " = "
 >> 59     let sep_comment     = del /[ \t]*#[ \t]*/ " # "
 >> 60     let record_comment  = [ label "comment" . sep_comment . store
/([^ \t\n].*)?/ ]
 >> 61     let record          = option . sep_assign . value_all .
record_comment?
 >> 62     let record_not      = label "comment" . store (/([^ \t\n].*)?/ -
lens_ctype record)
 >> 63     let comment         = del /#[ \t]*/ "# " . ( [ record . [ label
"commented" ] ] | [ record_not ] )
 >> 64     let line            = del /[ \t]*/ "" . ( comment | [ record ] )
. del "\n" "\n"
 >> 65     let lns             = line *

The first is a regex problem: I want to match double-quoted c-style
strings, ie strings with escape sequences such as "\"", "\\\"" and so on.
The regex I've crafted (line#50) evidently fits the bill - try modifying
the input test values (line#48) to verify - so I don't understand why the
derived lens (line#56) is failing, and thereby causing this "ambiguous
concatenation" error:

 >> Syntax error in lens definition
 >> configobj.aug:61.4-.75:Failed to compile record
 >> configobj.aug:61.26-.75:exception: ambiguous concatenation
 >>       First regexp: /([a-z]([a-z_]*[a-z])?)([ \t]*=[
\t]*)((((true|false)))|(((0|[1-9][0-9]*)))|(((((0|[1-9][0-9]*)))(\\.[0-9]+)))|((")(([^\n"\\][^\n"\\]*\\\\|\\\\)([^\n\\][^\n"\\]*\\\\)*\\\\(([^\n"\\][^\n"\\]*\\\\|\\\\)([^\n\\][^\n"\\]*\\\\)*\\\\)*(([^\n"\\][^\n"\\]*\\\\|\\\\)([^\n\\][^\n"\\]*\\\\)*([^\n\\][^\n"\\]*|)|[^\n"\\][^\n"\\]*|)|([^\n"\\][^\n"\\]*\\\\|\\\\)([^\n\\][^\n"\\]*\\\\)*([^\n\\][^\n"\\]*|)|[^\n"\\][^\n"\\]*|)(")))/
 >>       Second regexp: /(([ \t]*#[ \t]*)(([^ \t\n].*)?))?/
 >>       'a="\\"#"' can be split into
 >>       'a="\\"|=|#"'
 >>
 >>      and
 >>       'a="\\"#"|=|'  <----- not possible per the regex
 >>
 >>     First lens: configobj.aug:61.26-.57:
 >>     Second lens: configobj.aug:61.60-.75:

The second problem - you'll see if the first is fixed - is a limitation of
augeas' tree-text conversion, the inability to differentiate trees on
depth. This generates the error "exception: overlapping lenses in tree
union.put" and crops up in two locations:

 '[ record . [ label "commented" ] ]' (line#63) ----vs---- '[ record_not ]'
(line#63)
    ::: The "record_not" label of "comment" is also a possible valid label
of the "record" lens [line#52]. Hacky workaround is to change the label to
an invalid key, ie "comment2", etc.
 '[ record . [ label "commented" ] ]' (line#63) ----vs---- '[ record ]'
(line#64)
    ::: Unlike previous, no hacky workaround.

Obviously this can be fixed by scanning the *depth* of the tree. In both
cases, one branch is guaranteed to have a subnode with the label
"commented" unlike the other. While augeas doesn't implement this, there
was a suggestion on the mailing list regarding a lens-based workaround[1]
that I didn't understand. I'd appreciate if someone could provide a
concrete example for my case.


Sincerely,


[1] https://www.redhat.com/archives/augeas-devel/2009-June/msg00088.html
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