Support some escape sequences, in particular character escape sequences,

inside \w arguments, and skip most other escape sequences when measuring
the output length in this way because most escape sequences contribute
little or nothing to text width: for example, consider font escapes in
terminal output.

This implementation is very rudimentary.  In particular, it assumes that
every character has the same width.  No attempt is made to detect
double-width or zero-width Unicode characters or to take dependencies on
output devices or fonts into account.  These limitations are hard to
avoid because mandoc has to interpolate \w at the parsing stage when the
output device is not yet known.  I really do not want the content of the
syntax tree to depend on the output device.

Feature requested by Paul <Eggert at cs dot ucla dot edu>, who also
submitted a patch, but i chose to commit this very different patch
with almost the same functionality.
His input was still very valuable because complete support for \w is
out of the question, and consequently, the main task is identifying
subsets of the feature that are needed for real-world manual pages
and can be supported without uprooting the whole forest.

3 files changed, 28 insertions, 6 deletions

diff --git a/regress/roff/esc/w.in b/regress/roff/esc/w.in
index c30a31ac..59a9bdb5 100644
--- a/regress/roff/esc/w.in
+++ b/regress/roff/esc/w.in
@@ -1,4 +1,4 @@
-.\" $OpenBSD: w.in,v 1.4 2022/06/08 13:08:00 schwarze Exp $
+.\" $OpenBSD: w.in,v 1.5 2023/10/23 20:07:19 schwarze Exp $
 .Dd $Mdocdate$
 .Dt ESC-W 1
 .Os
@@ -13,6 +13,20 @@ character: \w'n'
 blank: \w' '
 .br
 text: \w'text'
+.br
+special: \w'\(bu'
+.br
+numbered: \w'\N'100''
+.br
+Unicode: \w'\[u2013]'
+.br
+overstrike: \w'\o'ab''
+.br
+undefined: \w'\G'
+.br
+zero-width: \w'\fB\&\fP'
+.br
+skipchar: \w'a\zb\z\(buc'
 .Ss Argument delimiters
 unsupported \er: \w\rM\ru
 .br
diff --git a/regress/roff/esc/w.out_ascii b/regress/roff/esc/w.out_ascii
index 7ed32ece..a8fdce54 100644
--- a/regress/roff/esc/w.out_ascii
+++ b/regress/roff/esc/w.out_ascii
@@ -8,6 +8,13 @@ DDEESSCCRRIIPPTTIIOONN
      character: 24
      blank: 24
      text: 96
+     special: 24
+     numbered: 24
+     Unicode: 24
+     overstrike: 24
+     undefined: 24
+     zero-width: 0
+     skipchar: 48
 
    AArrgguummeenntt ddeelliimmiitteerrss
      unsupported \r: 24u
@@ -27,4 +34,4 @@ DDEESSCCRRIIPPTTIIOONN
      overstrike: 24u
      unterminated: 72
 
-OpenBSD                          June 8, 2022                          OpenBSD
+OpenBSD                        October 23, 2023                        OpenBSD
diff --git a/regress/roff/esc/w.out_lint b/regress/roff/esc/w.out_lint
index fd2a0948..9c6417c5 100644
--- a/regress/roff/esc/w.out_lint
+++ b/regress/roff/esc/w.out_lint
@@ -1,4 +1,5 @@
-mandoc: w.in:17:20: UNSUPP: unsupported escape sequence: \r
-mandoc: w.in:17:23: UNSUPP: unsupported escape sequence: \r
-mandoc: w.in:23:16: WARNING: undefined escape, printing literally: \G
-mandoc: w.in:51:15: ERROR: incomplete escape sequence: \w'foo
+mandoc: w.in:25:15: WARNING: undefined escape, printing literally: \G
+mandoc: w.in:31:20: UNSUPP: unsupported escape sequence: \r
+mandoc: w.in:31:23: UNSUPP: unsupported escape sequence: \r
+mandoc: w.in:37:16: WARNING: undefined escape, printing literally: \G
+mandoc: w.in:65:15: ERROR: incomplete escape sequence: \w'foo