To prevent infinite recursion while expanding eqn(7) definitions,

we must not reset the recursion counter when moving beyond the end
of the *previous* expansion, but we may only do so when moving
beyond the rightmost position reached by *any* expansion in the
current equation.  This matters because definitions can nest;
consider:

.EQ
define inner "content"
define outer "inner outer"
outer
.EN

This endless loop was found by tb@ using afl(1).

Incidentally, GNU eqn(1) also performs an infinite loop in this
situation and then crashes when memory runs out, but that's not an
excuse for nasty behaviour of mandoc(1).

While here, consistently print the expanded content even when the
expansion is finally truncated.  While that is not likely to help
end-users, it may help authors of eqn(7) code to understand what's
going on.  Besides, it sends a very clear signal that something is
amiss, which was easy to miss in the past unless people
enabled -W error or used -T lint.

3 files changed, 76 insertions, 7 deletions

diff --git a/regress/eqn/define/infinite.in b/regress/eqn/define/infinite.in
index 420e6376..31a3f646 100644
--- a/regress/eqn/define/infinite.in
+++ b/regress/eqn/define/infinite.in
@@ -1,5 +1,5 @@
-.\" $OpenBSD: infinite.in,v 1.2 2017/07/04 14:53:23 schwarze Exp $
-.Dd $Mdocdate: July 4 2017 $
+.\" $OpenBSD: infinite.in,v 1.3 2022/04/13 20:19:18 schwarze Exp $
+.Dd $Mdocdate: April 13 2022 $
 .Dt DEFINE-INFINITE 1
 .Os
 .Sh NAME
@@ -29,3 +29,11 @@ trailing position:
 define key 'prefix key' key
 .EN
 eol
+.Pp
+nested expansion:
+.EQ
+define inner "content"
+define outer "inner outer"
+outer
+.EN
+eol
diff --git a/regress/eqn/define/infinite.out_ascii b/regress/eqn/define/infinite.out_ascii
index 7219ce5b..a756abbb 100644
--- a/regress/eqn/define/infinite.out_ascii
+++ b/regress/eqn/define/infinite.out_ascii
@@ -4,12 +4,72 @@ NNAAMMEE
      ddeeffiinnee--iinnffiinniittee - infinite recursion in define statements
 
 DDEESSCCRRIIPPTTIIOONN
-     alone: eol
+     alone: _k_e_y eol
 
-     leading position: eol
+     leading position: _k_e_y _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x eol
 
-     middle position: eol
+     middle position: _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _k_e_y
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x
+     _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x _s_u_f_f_i_x eol
 
-     trailing position: eol
+     trailing position: _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x _p_r_e_f_i_x
+     _p_r_e_f_i_x _k_e_y eol
 
-OpenBSD                          July 4, 2017                          OpenBSD
+     nested expansion: _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t
+     _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t
+     _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t
+     _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t
+     _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t
+     _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t
+     _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t
+     _c_o_n_t_e_n_t _c_o_n_t_e_n_t _c_o_n_t_e_n_t _o_u_t_e_r eol
+
+OpenBSD                         April 13, 2022                         OpenBSD
diff --git a/regress/eqn/define/infinite.out_lint b/regress/eqn/define/infinite.out_lint
index 43089bb3..245aa523 100644
--- a/regress/eqn/define/infinite.out_lint
+++ b/regress/eqn/define/infinite.out_lint
@@ -2,3 +2,4 @@ mandoc: infinite.in:10:2: ERROR: input stack limit exceeded, infinite loop?
 mandoc: infinite.in:16:2: ERROR: input stack limit exceeded, infinite loop?
 mandoc: infinite.in:22:2: ERROR: input stack limit exceeded, infinite loop?
 mandoc: infinite.in:28:2: ERROR: input stack limit exceeded, infinite loop?
+mandoc: infinite.in:34:2: ERROR: input stack limit exceeded, infinite loop?