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.

7 files changed, 113 insertions, 0 deletions

diff --git a/regress/mdoc/Tg/Makefile b/regress/mdoc/Tg/Makefile
new file mode 100644
index 00000000..7f538766
--- /dev/null
+++ b/regress/mdoc/Tg/Makefile
@@ -0,0 +1,8 @@
+# $OpenBSD: Makefile,v 1.1 2020/03/13 00:31:06 schwarze Exp $
+
+REGRESS_TARGETS = warn
+TAG_TARGETS	= warn
+LINT_TARGETS	= warn
+HTML_TARGETS	= warn
+
+.include <bsd.regress.mk>
diff --git a/regress/mdoc/Tg/warn.in b/regress/mdoc/Tg/warn.in
new file mode 100644
index 00000000..e36f4506
--- /dev/null
+++ b/regress/mdoc/Tg/warn.in
@@ -0,0 +1,34 @@
+.\" $OpenBSD: warn.in,v 1.1 2020/03/13 00:31:06 schwarze Exp $
+.Dd $Mdocdate: March 13 2020 $
+.Dt TG-WARN 1
+.Os
+.Sh NAME
+.Nm Tg-warn
+.Nd warnings about tagging macros
+.Sh DESCRIPTION
+BEGINTEST
+.Pp
+.Tg start
+initial
+text
+.Tg
+.Ic macro
+.Tg "" ignored arguments
+too many
+.Tg \&badstart
+badstart
+.Tg badend\&
+badend
+.Tg "white space"
+whitespace
+.Tg sub
+.Tg double
+.Ss Subsection
+subtext
+.Tg examples
+.Sh EXAMPLES
+example
+text
+.Pp
+ENDTEST
+.Tg
diff --git a/regress/mdoc/Tg/warn.out_ascii b/regress/mdoc/Tg/warn.out_ascii
new file mode 100644
index 00000000..8dee9aed
--- /dev/null
+++ b/regress/mdoc/Tg/warn.out_ascii
@@ -0,0 +1,19 @@
+TG-WARN(1)                  General Commands Manual                 TG-WARN(1)
+
+NNAAMMEE
+     TTgg--wwaarrnn - warnings about tagging macros
+
+DDEESSCCRRIIPPTTIIOONN
+     BEGINTEST
+
+     initial text mmaaccrroo too many badstart badend whitespace
+
+   SSuubbsseeccttiioonn
+     subtext
+
+EEXXAAMMPPLLEESS
+     example text
+
+     ENDTEST
+
+OpenBSD                         March 13, 2020                         OpenBSD
diff --git a/regress/mdoc/Tg/warn.out_html b/regress/mdoc/Tg/warn.out_html
new file mode 100644
index 00000000..b4d3cf74
--- /dev/null
+++ b/regress/mdoc/Tg/warn.out_html
@@ -0,0 +1,11 @@
+<p class="Pp"><mark id="start"></mark>initial text
+    <a class="permalink" href="#macro"><code class="Ic" id="macro">macro</code></a>
+    too many badstart badend whitespace <mark id="sub"></mark></p>
+<section class="Ss">
+<h2 class="Ss" id="double"><a class="permalink" href="#double">Subsection</a></h2>
+<p class="Pp">subtext</p>
+</section>
+</section>
+<section class="Sh">
+<h1 class="Sh" id="examples"><a class="permalink" href="#examples">EXAMPLES</a></h1>
+<p class="Pp">example text</p>
diff --git a/regress/mdoc/Tg/warn.out_lint b/regress/mdoc/Tg/warn.out_lint
new file mode 100644
index 00000000..39c1f541
--- /dev/null
+++ b/regress/mdoc/Tg/warn.out_lint
@@ -0,0 +1,6 @@
+mandoc: warn.in:16:2: WARNING: skipping empty macro: Tg
+mandoc: warn.in:16:8: ERROR: skipping excess arguments: Tg ... ignored
+mandoc: warn.in:18:5: ERROR: skipping tag containing whitespace: Tg \&badstart
+mandoc: warn.in:20:11: ERROR: skipping tag containing whitespace: Tg badend\&
+mandoc: warn.in:22:10: ERROR: skipping tag containing whitespace: Tg white space
+mandoc: warn.in:34:2: WARNING: skipping empty macro: Tg
diff --git a/regress/mdoc/Tg/warn.out_markdown b/regress/mdoc/Tg/warn.out_markdown
new file mode 100644
index 00000000..87204424
--- /dev/null
+++ b/regress/mdoc/Tg/warn.out_markdown
@@ -0,0 +1,30 @@
+TG-WARN(1) - General Commands Manual
+
+# NAME
+
+**Tg-warn** - warnings about tagging macros
+
+# DESCRIPTION
+
+BEGINTEST
+
+initial
+text
+**macro**
+too many
+badstart
+badend
+whitespace
+
+## Subsection
+
+subtext
+
+# EXAMPLES
+
+example
+text
+
+ENDTEST
+
+OpenBSD - March 13, 2020
diff --git a/regress/mdoc/Tg/warn.out_tag b/regress/mdoc/Tg/warn.out_tag
new file mode 100644
index 00000000..e1fc141c
--- /dev/null
+++ b/regress/mdoc/Tg/warn.out_tag
@@ -0,0 +1,5 @@
+start 9
+macro 9
+sub 9
+double 11
+examples 14