Split tagging into a validation part including prioritization

in tag.{h,c} and {mdoc,man}_validate.c
and into a formatting part including command line argument checking
in term_tag.{h,c}, html.c, and {mdoc|man}_{term|html}.c.

Immediate functional benefits include:
* Improved prioritization of automatic tags for .Em and .Sy.
* Avoiding bogus automatic tags when .Em, .Fn, or .Sy are explicitly tagged.
* Explicit tagging of .Er and .Fl now works in HTML output.
* Automatic tagging of .IP and .TP now works in HTML output.
But mainly, this patch provides clean earth to build further improvements on.

Technical changes:
* Main program: Write a tag file for ASCII and UTF-8 output only.
* All formatters: There is no more need to delay writing the tags.
* mdoc(7)+man(7) formatters: No more need for elaborate syntax tree inspection.
* HTML formatter: If available, use the "string" attribute as the tag.
* HTML formatter: New function to write permalinks, to reduce code duplication.

Style cleanup in the vicinity while here:
* mdoc(7) terminal formatter: To set up bold font for children,
defer to termp_bold_pre() rather than calling term_fontpush() manually.
* mdoc(7) terminal formatter: Garbage collect some duplicate functions.
* mdoc(7) HTML formatter: Unify <code> handling, delete redundant functions.
* Where possible, use switch statements rather than if cascades.
* Get rid of some more Yoda notation.

The necessity for such changes was first discussed with kn@, but i didn't
bother him with a request to review the resulting -673/+782 line patch.

1 files changed, 55 insertions, 18 deletions

diff --git a/mandoc_headers.3 b/mandoc_headers.3
index 9e2c1752..f55d491d 100644
--- a/mandoc_headers.3
+++ b/mandoc_headers.3
@@ -1,6 +1,6 @@
 .\"	$Id$
 .\"
-.\" Copyright (c) 2014-2019 Ingo Schwarze <schwarze@openbsd.org>
+.\" Copyright (c) 2014-2020 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
@@ -232,6 +232,30 @@ and the functions
 .Fn mandoc_xr_get ,
 and
 .Fn mandoc_xr_free .
+.It Qq Pa tag.h
+Internal interfaces to tag syntax tree nodes,
+for use by validation modules only.
+.Pp
+Requires
+.In limits.h
+for
+.Dv INT_MAX .
+.Pp
+Provides the functions
+.Fn tag_alloc ,
+.Fn tag_put ,
+.Fn tag_check ,
+and
+.Fn tag_free
+and some
+.Dv TAG_*
+constants.
+.Pp
+Uses the type
+.Vt struct roff_node
+from
+.Qq Pa roff.h
+as an opaque type for function prototypes.
 .El
 .Pp
 The following two require
@@ -587,6 +611,33 @@ When this header is included, the same file should not include
 .Qq Pa html.h
 or
 .Qq Pa mansearch.h .
+.It Qq Pa tag_term.h
+Requires
+.In sys/types.h
+for
+.Vt size_t
+and
+.In stdio.h
+for
+.Vt FILE .
+.Pp
+Provides an interface to generate
+.Xr ctags 1
+files for the
+.Ic :t
+functionality mentioned in
+.Xr man 1 .
+.Pp
+Uses the type
+.Vt struct roff_node
+from
+.Qq Pa roff.h
+as an opaque type for function prototypes.
+.Pp
+When this header is included, the same file should not include
+.Qq Pa html.h
+or
+.Qq Pa mansearch.h .
 .It Qq Pa html.h
 Requires
 .In sys/types.h
@@ -629,25 +680,10 @@ from
 as opaque types for function prototypes.
 .Pp
 When this header is included, the same file should not include
-.Qq Pa term.h
+.Qq Pa term.h ,
+.Qq Pa tab_term.h ,
 or
 .Qq Pa mansearch.h .
-.It Qq Pa tag.h
-Requires
-.In sys/types.h
-for
-.Vt size_t
-and
-.In limits.h
-for
-.Dv INT_MAX .
-.Pp
-Provides an interface to generate
-.Xr ctags 1
-files for the
-.Ic :t
-functionality mentioned in
-.Xr man 1 .
 .It Qq Pa main.h
 Provides the top level steering functions for all formatters.
 .Pp
@@ -700,6 +736,7 @@ as an opaque type for function prototypes.
 When this header is included, the same file should not include
 .Qq Pa out.h ,
 .Qq Pa term.h ,
+.Qq Pa tab_term.h ,
 or
 .Qq Pa html.h .
 .El