Don't dereference NULL pointers when formatting missing denominators,

[mandoc.git] / mandoc.3

.\"     $Id: mandoc.3,v 1.29 2014/11/26 23:42:14 schwarze Exp $
.\"
.\" Copyright (c) 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
.\" Copyright (c) 2010 Ingo Schwarze <schwarze@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.Dd $Mdocdate: November 26 2014 $
.Dt MANDOC 3
.Os
.Sh NAME
.Nm mandoc ,
.Nm man_deroff ,
.Nm man_meta ,
.Nm man_mparse ,
.Nm man_node ,
.Nm mdoc_deroff ,
.Nm mdoc_meta ,
.Nm mdoc_node ,
.Nm mparse_alloc ,
.Nm mparse_free ,
.Nm mparse_getkeep ,
.Nm mparse_keep ,
.Nm mparse_open ,
.Nm mparse_readfd ,
.Nm mparse_reset ,
.Nm mparse_result ,
.Nm mparse_strerror ,
.Nm mparse_strlevel
.Nm mparse_wait ,
.Nd mandoc macro compiler library
.Sh LIBRARY
.Lb libmandoc
.Sh SYNOPSIS
.In sys/types.h
.In mandoc.h
.Fd "#define ASCII_NBRSP"
.Fd "#define ASCII_HYPH"
.Fd "#define ASCII_BREAK"
.Ft struct mparse *
.Fo mparse_alloc
.Fa "int options"
.Fa "enum mandoclevel wlevel"
.Fa "mandocmsg mmsg"
.Fa "const struct mchars *mchars"
.Fa "char *defos"
.Fc
.Ft void
.Fo (*mandocmsg)
.Fa "enum mandocerr errtype"
.Fa "enum mandoclevel level"
.Fa "const char *file"
.Fa "int line"
.Fa "int col"
.Fa "const char *msg"
.Fc
.Ft void
.Fo mparse_free
.Fa "struct mparse *parse"
.Fc
.Ft const char *
.Fo mparse_getkeep
.Fa "const struct mparse *parse"
.Fc
.Ft void
.Fo mparse_keep
.Fa "struct mparse *parse"
.Fc
.Ft "enum mandoclevel"
.Fo mparse_open
.Fa "struct mparse *parse"
.Fa "int *fd"
.Fa "const char *fname"
.Fc
.Ft "enum mandoclevel"
.Fo mparse_readfd
.Fa "struct mparse *parse"
.Fa "int fd"
.Fa "const char *fname"
.Fc
.Ft void
.Fo mparse_reset
.Fa "struct mparse *parse"
.Fc
.Ft void
.Fo mparse_result
.Fa "struct mparse *parse"
.Fa "struct mdoc **mdoc"
.Fa "struct man **man"
.Fa "char **sodest"
.Fc
.Ft "const char *"
.Fo mparse_strerror
.Fa "enum mandocerr"
.Fc
.Ft "const char *"
.Fo mparse_strlevel
.Fa "enum mandoclevel"
.Fc
.Ft "enum mandoclevel"
.Fo mparse_wait
.Fa "struct mparse *parse"
.Fc
.In sys/types.h
.In mandoc.h
.In mdoc.h
.Ft void
.Fo mdoc_deroff
.Fa "char **dest"
.Fa "const struct mdoc_node *node"
.Fc
.Ft "const struct mdoc_meta *"
.Fo mdoc_meta
.Fa "const struct mdoc *mdoc"
.Fc
.Ft "const struct mdoc_node *"
.Fo mdoc_node
.Fa "const struct mdoc *mdoc"
.Fc
.Vt extern const char * const * mdoc_argnames;
.Vt extern const char * const * mdoc_macronames;
.In sys/types.h
.In mandoc.h
.In man.h
.Ft void
.Fo man_deroff
.Fa "char **dest"
.Fa "const struct man_node *node"
.Fc
.Ft "const struct man_meta *"
.Fo man_meta
.Fa "const struct man *man"
.Fc
.Ft "const struct mparse *"
.Fo man_mparse
.Fa "const struct man *man"
.Fc
.Ft "const struct man_node *"
.Fo man_node
.Fa "const struct man *man"
.Fc
.Vt extern const char * const * man_macronames;
.Sh DESCRIPTION
The
.Nm mandoc
library parses a
.Ux
manual into an abstract syntax tree (AST).
.Ux
manuals are composed of
.Xr mdoc 7
or
.Xr man 7 ,
and may be mixed with
.Xr roff 7 ,
.Xr tbl 7 ,
and
.Xr eqn 7
invocations.
.Pp
The following describes a general parse sequence:
.Bl -enum
.It
initiate a parsing sequence with
.Xr mchars_alloc 3
and
.Fn mparse_alloc ;
.It
parse files or file descriptors with
.Fn mparse_readfd ;
.It
retrieve a parsed syntax tree, if the parse was successful, with
.Fn mparse_result ;
.It
iterate over parse nodes with
.Fn mdoc_node
or
.Fn man_node ;
.It
free all allocated memory with
.Fn mparse_free
and
.Xr mchars_free 3 ,
or invoke
.Fn mparse_reset
and parse new files.
.El
.Sh REFERENCE
This section documents the functions, types, and variables available
via
.In mandoc.h ,
with the exception of those documented in
.Xr mandoc_escape 3
and
.Xr mchars_alloc 3 .
.Ss Types
.Bl -ohang
.It Vt "enum mandocerr"
A fatal error, error, or warning message during parsing.
.It Vt "enum mandoclevel"
A classification of an
.Vt "enum mandocerr"
as regards system operation.
.It Vt "struct mchars"
An opaque pointer to a a character table.
Created with
.Xr mchars_alloc 3
and freed with
.Xr mchars_free 3 .
.It Vt "struct mparse"
An opaque pointer to a running parse sequence.
Created with
.Fn mparse_alloc
and freed with
.Fn mparse_free .
This may be used across parsed input if
.Fn mparse_reset
is called between parses.
.It Vt "mandocmsg"
A prototype for a function to handle fatal error, error, and warning
messages emitted by the parser.
.El
.Ss Functions
.Bl -ohang
.It Fn man_deroff
Obtain a text-only representation of a
.Vt struct man_node ,
including text contained in its child nodes.
To be used on children of the pointer returned from
.Fn man_node .
When it is no longer needed, the pointer returned from
.Fn man_deroff
can be passed to
.Xr free 3 .
.It Fn man_meta
Obtain the meta-data of a successful
.Xr man 7
parse.
This may only be used on a pointer returned by
.Fn mparse_result .
Declared in
.In man.h ,
implemented in
.Pa man.c .
.It Fn man_mparse
Get the parser used for the current output.
Declared in
.In man.h ,
implemented in
.Pa man.c .
.It Fn man_node
Obtain the root node of a successful
.Xr man 7
parse.
This may only be used on a pointer returned by
.Fn mparse_result .
Declared in
.In man.h ,
implemented in
.Pa man.c .
.It Fn mdoc_deroff
Obtain a text-only representation of a
.Vt struct mdoc_node ,
including text contained in its child nodes.
To be used on children of the pointer returned from
.Fn mdoc_node .
When it is no longer needed, the pointer returned from
.Fn mdoc_deroff
can be passed to
.Xr free 3 .
.It Fn mdoc_meta
Obtain the meta-data of a successful
.Xr mdoc
parse.
This may only be used on a pointer returned by
.Fn mparse_result .
Declared in
.In mdoc.h ,
implemented in
.Pa mdoc.c .
.It Fn mdoc_node
Obtain the root node of a successful
.Xr mdoc
parse.
This may only be used on a pointer returned by
.Fn mparse_result .
Declared in
.In mdoc.h ,
implemented in
.Pa mdoc.c .
.It Fn mparse_alloc
Allocate a parser.
The arguments have the following effect:
.Bl -tag -offset 5n -width inttype
.It Ar options
When the
.Dv MPARSE_MDOC
or
.Dv MPARSE_MAN
bit is set, only that parser is used.
Otherwise, the document type is automatically detected.
.Pp
When the
.Dv MPARSE_SO
bit is set,
.Xr roff 7
.Ic \&so
file inclusion requests are always honoured.
Otherwise, if the request is the only content in an input file,
only the file name is remembered, to be returned in the
.Fa sodest
argument of
.Fn mparse_result .
.Pp
When the
.Dv MPARSE_QUICK
bit is set, parsing is aborted after the NAME section.
This is for example useful in
.Xr makewhatis 8
.Fl Q
to quickly build minimal databases.
.It Ar wlevel
Can be set to
.Dv MANDOCLEVEL_FATAL ,
.Dv MANDOCLEVEL_ERROR ,
or
.Dv MANDOCLEVEL_WARNING .
Messages below the selected level will be suppressed.
.It Ar mmsg
A callback function to handle errors and warnings.
See
.Pa main.c
for an example.
.It Ar mchars
An opaque pointer to a a character table obtained from
.Xr mchars_alloc 3 .
.It Ar defos
A default string for the
.Xr mdoc 7
.Sq \&Os
macro, overriding the
.Dv OSNAME
preprocessor definition and the results of
.Xr uname 3 .
.El
.Pp
The same parser may be used for multiple files so long as
.Fn mparse_reset
is called between parses.
.Fn mparse_free
must be called to free the memory allocated by this function.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_free
Free all memory allocated by
.Fn mparse_alloc .
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_getkeep
Acquire the keep buffer.
Must follow a call of
.Fn mparse_keep .
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_keep
Instruct the parser to retain a copy of its parsed input.
This can be acquired with subsequent
.Fn mparse_getkeep
calls.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_open
If the
.Fa fname
ends in
.Pa .gz ,
open with
.Xr gunzip 1 ;
otherwise, with
.Xr open 2 .
If
.Xr open 2
fails, append
.Pa .gz
and try with
.Xr gunzip 1 .
Return a file descriptor open for reading in
.Fa fd ,
or -1 on failure.
It can be passed to
.Fn mparse_readfd
or used directly.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_readfd
Parse a file or file descriptor.
If
.Va fd
is -1, open
.Va fname
with
.Fn mparse_open .
Otherwise,
.Va fname
is assumed to be the name associated with
.Va fd .
Calls
.Fn mparse_wait
before returning.
This function may be called multiple times with different parameters; however,
.Fn mparse_reset
should be invoked between parses.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_reset
Reset a parser so that
.Fn mparse_readfd
may be used again.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_result
Obtain the result of a parse.
Only successful parses
.Po
i.e., those where
.Fn mparse_readfd
returned less than MANDOCLEVEL_FATAL
.Pc
should invoke this function, in which case one of the three pointers will
be filled in.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_strerror
Return a statically-allocated string representation of an error code.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_strlevel
Return a statically-allocated string representation of a level code.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_wait
Bury a
.Xr gunzip 1
child process that was spawned with
.Fn mparse_open .
To be called after the parse sequence is complete.
Not needed after
.Fn mparse_readfd ,
but does no harm in that case, either.
Returns
.Dv MANDOCLEVEL_OK
on success and
.Dv MANDOCLEVEL_SYSERR
on failure, that is, when
.Xr wait 2
fails, or when
.Xr gunzip 1
died from a signal or exited with non-zero status.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.El
.Ss Variables
.Bl -ohang
.It Va man_macronames
The string representation of a man macro as indexed by
.Vt "enum mant" .
.It Va mdoc_argnames
The string representation of a mdoc macro argument as indexed by
.Vt "enum mdocargt" .
.It Va mdoc_macronames
The string representation of a mdoc macro as indexed by
.Vt "enum mdoct" .
.El
.Sh IMPLEMENTATION NOTES
This section consists of structural documentation for
.Xr mdoc 7
and
.Xr man 7
syntax trees and strings.
.Ss Man and Mdoc Strings
Strings may be extracted from mdoc and man meta-data, or from text
nodes (MDOC_TEXT and MAN_TEXT, respectively).
These strings have special non-printing formatting cues embedded in the
text itself, as well as
.Xr roff 7
escapes preserved from input.
Implementing systems will need to handle both situations to produce
human-readable text.
In general, strings may be assumed to consist of 7-bit ASCII characters.
.Pp
The following non-printing characters may be embedded in text strings:
.Bl -tag -width Ds
.It Dv ASCII_NBRSP
A non-breaking space character.
.It Dv ASCII_HYPH
A soft hyphen.
.It Dv ASCII_BREAK
A breakable zero-width space.
.El
.Pp
Escape characters are also passed verbatim into text strings.
An escape character is a sequence of characters beginning with the
backslash
.Pq Sq \e .
To construct human-readable text, these should be intercepted with
.Xr mandoc_escape 3
and converted with one the functions described in
.Xr mchars_alloc 3 .
.Ss Man Abstract Syntax Tree
This AST is governed by the ontological rules dictated in
.Xr man 7
and derives its terminology accordingly.
.Pp
The AST is composed of
.Vt struct man_node
nodes with element, root and text types as declared by the
.Va type
field.
Each node also provides its parse point (the
.Va line ,
.Va sec ,
and
.Va pos
fields), its position in the tree (the
.Va parent ,
.Va child ,
.Va next
and
.Va prev
fields) and some type-specific data.
.Pp
The tree itself is arranged according to the following normal form,
where capitalised non-terminals represent nodes.
.Pp
.Bl -tag -width "ELEMENTXX" -compact
.It ROOT
\(<- mnode+
.It mnode
\(<- ELEMENT | TEXT | BLOCK
.It BLOCK
\(<- HEAD BODY
.It HEAD
\(<- mnode*
.It BODY
\(<- mnode*
.It ELEMENT
\(<- ELEMENT | TEXT*
.It TEXT
\(<- [[:ascii:]]*
.El
.Pp
The only elements capable of nesting other elements are those with
next-line scope as documented in
.Xr man 7 .
.Ss Mdoc Abstract Syntax Tree
This AST is governed by the ontological
rules dictated in
.Xr mdoc 7
and derives its terminology accordingly.
.Qq In-line
elements described in
.Xr mdoc 7
are described simply as
.Qq elements .
.Pp
The AST is composed of
.Vt struct mdoc_node
nodes with block, head, body, element, root and text types as declared
by the
.Va type
field.
Each node also provides its parse point (the
.Va line ,
.Va sec ,
and
.Va pos
fields), its position in the tree (the
.Va parent ,
.Va child ,
.Va nchild ,
.Va next
and
.Va prev
fields) and some type-specific data, in particular, for nodes generated
from macros, the generating macro in the
.Va tok
field.
.Pp
The tree itself is arranged according to the following normal form,
where capitalised non-terminals represent nodes.
.Pp
.Bl -tag -width "ELEMENTXX" -compact
.It ROOT
\(<- mnode+
.It mnode
\(<- BLOCK | ELEMENT | TEXT
.It BLOCK
\(<- HEAD [TEXT] (BODY [TEXT])+ [TAIL [TEXT]]
.It ELEMENT
\(<- TEXT*
.It HEAD
\(<- mnode*
.It BODY
\(<- mnode* [ENDBODY mnode*]
.It TAIL
\(<- mnode*
.It TEXT
\(<- [[:ascii:]]*
.El
.Pp
Of note are the TEXT nodes following the HEAD, BODY and TAIL nodes of
the BLOCK production: these refer to punctuation marks.
Furthermore, although a TEXT node will generally have a non-zero-length
string, in the specific case of
.Sq \&.Bd \-literal ,
an empty line will produce a zero-length string.
Multiple body parts are only found in invocations of
.Sq \&Bl \-column ,
where a new body introduces a new phrase.
.Pp
The
.Xr mdoc 7
syntax tree accommodates for broken block structures as well.
The ENDBODY node is available to end the formatting associated
with a given block before the physical end of that block.
It has a non-null
.Va end
field, is of the BODY
.Va type ,
has the same
.Va tok
as the BLOCK it is ending, and has a
.Va pending
field pointing to that BLOCK's BODY node.
It is an indirect child of that BODY node
and has no children of its own.
.Pp
An ENDBODY node is generated when a block ends while one of its child
blocks is still open, like in the following example:
.Bd -literal -offset indent
\&.Ao ao
\&.Bo bo ac
\&.Ac bc
\&.Bc end
.Ed
.Pp
This example results in the following block structure:
.Bd -literal -offset indent
BLOCK Ao
    HEAD Ao
    BODY Ao
        TEXT ao
        BLOCK Bo, pending -> Ao
            HEAD Bo
            BODY Bo
                TEXT bo
                TEXT ac
                ENDBODY Ao, pending -> Ao
                TEXT bc
TEXT end
.Ed
.Pp
Here, the formatting of the
.Sq \&Ao
block extends from TEXT ao to TEXT ac,
while the formatting of the
.Sq \&Bo
block extends from TEXT bo to TEXT bc.
It renders as follows in
.Fl T Ns Cm ascii
mode:
.Pp
.Dl <ao [bo ac> bc] end
.Pp
Support for badly-nested blocks is only provided for backward
compatibility with some older
.Xr mdoc 7
implementations.
Using badly-nested blocks is
.Em strongly discouraged ;
for example, the
.Fl T Ns Cm html
and
.Fl T Ns Cm xhtml
front-ends to
.Xr mandoc 1
are unable to render them in any meaningful way.
Furthermore, behaviour when encountering badly-nested blocks is not
consistent across troff implementations, especially when using multiple
levels of badly-nested blocks.
.Sh SEE ALSO
.Xr mandoc 1 ,
.Xr mandoc_escape 3 ,
.Xr mandoc_malloc 3 ,
.Xr mchars_alloc 3 ,
.Xr eqn 7 ,
.Xr man 7 ,
.Xr mandoc_char 7 ,
.Xr mdoc 7 ,
.Xr roff 7 ,
.Xr tbl 7
.Sh AUTHORS
The
.Nm
library was written by
.An Kristaps Dzonsons Aq Mt kristaps@bsd.lv .