Implement a leading spaces macro request, `lsm', in analogy to

`blm'.
Implement two new number registers, \n[lsn] and \n[lss], which hold
the number of spaces and the horizontal space, respectively, which
would be inserted if the macro registered by `lsm' wasn't called.

* src/roff/troff/input.cpp (leading_spaces_macro_name,
leading_spaces_number, leading_spaces_space): New global
variables.
(leading_spaces_macro): New function.
(process_input_stack) <token::TOKEN_SPACE>: Handle `lsm'.
(init_input_requests): Register `lsm', \n[lsn], and \n[lss].

* NEWS, man/groff_diff.man, man/groff.man, doc/groff.texinfo
(Leading Spaces Traps): Document new requests and registers.

2 files changed, 40 insertions, 1 deletions

diff --git a/man/groff.man b/man/groff.man
index 4e59c25b..a63961ca 100644
--- a/man/groff.man
+++ b/man/groff.man
@@ -1873,6 +1873,15 @@ default scaling indicator\~\c
 .scaleindicator m ).
 .
 .TPx
+.REQ .lsm
+Unset the leading spaces macro.
+.
+.TPx
+.REQ .lsm "macro"
+Set the leading spaces macro to
+.IR macro .
+.
+.TPx
 .REQ .ls
 Change to the previous value of additional intra-line skip.
 .
@@ -3902,6 +3911,15 @@ image (set by
 Output line number.
 .
 .TPx
+.REG lsn
+The number of leading spaces of an input line.
+.
+.TPx
+.REG lss
+The horizontal space corresponding to the leading spaces of an input
+line.
+.
+.TPx
 .REG minutes
 The number of minutes after the hour.
 .
diff --git a/man/groff_diff.man b/man/groff_diff.man
index 7f39a50a..dcd70a0d 100644
--- a/man/groff_diff.man
+++ b/man/groff_diff.man
@@ -1767,6 +1767,19 @@ read-only number register
 is set to\~1 if in line-tabs mode, and 0 otherwise.
 .
 .TP
+.BI .lsm\  xx
+Set the leading spaces macro to
+.IR xx .
+If there are leading spaces in an input line, it is invoked instead of
+the usual troff behaviour; the leading spaces are removed.
+Registers
+.B \[rs]n[lsn]
+and
+.B \[rs]n[lss]
+hold the number of removed leading spaces and the corresponding
+horizontal space, respectively.
+.
+.TP
 .BI .mso\  file
 The same as the
 .B so
@@ -2900,7 +2913,7 @@ Zero if no magnification.
 .B \[rs]n[urx]
 .TQ
 .B \[rs]n[ury]
-These four registers are set by the
+These four read/\:write registers are set by the
 .B psbb
 request and contain the bounding box values (in PostScript units) of a
 given PostScript image.
@@ -2952,6 +2965,14 @@ Initialized at start-up.
 The current horizontal position at input line.
 .
 .TP
+.B \[rs]n[lsn]
+.TQ
+.B \[rs]n[lss]
+If there are leading spaces in an input line, these registers
+hold the number of leading spaces and the corresponding
+horizontal space, respectively.
+.
+.TP
 .B \[rs]n[minutes]
 The number of minutes after the hour.
 .