recognize ".if n" as true;

nothing fancy yet, no negation, no grammer, just that one letter;
from OpenBSD;
"looks fine" kristaps@

2 files changed, 26 insertions, 7 deletions

diff --git a/roff.7 b/roff.7
index ed75a1e3..f46fe62e 100644
--- a/roff.7
+++ b/roff.7
@@ -126,7 +126,15 @@ which may be separated by any intervening input (or not exist at all).
 Its syntax is equivalent to
 .Sx \&if .
 .Ss \&if
-Begins a conditional that always evaluates to false.
+Begins a conditional.
+Right now, the conditional evaluates to true
+if and only if it starts with the letter
+.Sy n ,
+indicating processing in
+.Xr nroff 1
+style as opposed to
+.Xr troff 1
+style.
 If a conditional is false, its children are not processed, but are
 syntactically interpreted to preserve the integrity of the input
 document.
@@ -249,7 +257,7 @@ Currently, it is ignored including its arguments,
 and the number of arguments is not checked.
 .Ss \&tr
 Output character translation.
-This macro is intended to have one argument, 
+This macro is intended to have one argument,
 consisting of an even number of characters.
 Currently, it is ignored including its arguments,
 and the number of arguments is not checked.
diff --git a/roff.c b/roff.c
index 17099449..20f22d96 100644
--- a/roff.c
+++ b/roff.c
@@ -575,7 +575,7 @@ roff_cond_sub(ROFF_ARGS)
 	ppos = pos;
 	rr = r->last->rule;
 
-	roffnode_cleanscope(r);
+	roff_cond_text(r, tok, bufp, szp, ln, ppos, pos, offs);
 
 	if (ROFF_MAX == (t = roff_parse(*bufp, &pos)))
 		return(ROFFRULE_DENY == rr ? ROFF_IGN : ROFF_CONT);
@@ -616,8 +616,10 @@ roff_cond_text(ROFF_ARGS)
 		return(ROFFRULE_DENY == rr ? ROFF_IGN : ROFF_CONT);
 	}
 
-	if (ep > st && '\\' != *(ep - 1))
+	if (ep > st && '\\' != *(ep - 1)) {
+		ep = '\0';
 		roffnode_pop(r);
+	}
 
 	roffnode_cleanscope(r);
 	return(ROFFRULE_DENY == rr ? ROFF_IGN : ROFF_CONT);
@@ -628,6 +630,7 @@ roff_cond_text(ROFF_ARGS)
 static enum rofferr
 roff_cond(ROFF_ARGS)
 {
+	int		 cpos;  /* position of the condition */
 	int		 sv;
 
 	/* Stack overflow! */
@@ -637,6 +640,8 @@ roff_cond(ROFF_ARGS)
 		return(ROFF_ERR);
 	}
 
+	cpos = pos;
+
 	if (ROFF_if == tok || ROFF_ie == tok) {
 		/*
 		 * Read ahead past the conditional.  FIXME: this does
@@ -667,9 +672,12 @@ roff_cond(ROFF_ARGS)
 	if ( ! roffnode_push(r, tok, ln, ppos))
 		return(ROFF_ERR);
 
-	/* TODO: here we would evaluate the conditional. */
+	/* XXX: Implement more conditionals. */
 
-	if (ROFF_el == tok) {
+	if (ROFF_if == tok || ROFF_ie == tok)
+		r->last->rule = 'n' == (*bufp)[cpos] ?
+		    ROFFRULE_ALLOW : ROFFRULE_DENY;
+	else if (ROFF_el == tok) {
 		/* 
 		 * An `.el' will get the value of the current rstack
 		 * entry set in prior `ie' calls or defaults to DENY.
@@ -678,7 +686,8 @@ roff_cond(ROFF_ARGS)
 			r->last->rule = ROFFRULE_DENY;
 		else
 			r->last->rule = r->rstack[r->rstackpos];
-	} else if (ROFF_ie == tok) {
+	}
+	if (ROFF_ie == tok) {
 		/*
 		 * An if-else will put the NEGATION of the current
 		 * evaluated conditional into the stack.
@@ -689,6 +698,8 @@ roff_cond(ROFF_ARGS)
 		else
 			r->rstack[r->rstackpos] = ROFFRULE_DENY;
 	}
+	if (r->last->parent && ROFFRULE_DENY == r->last->parent->rule)
+		r->last->rule = ROFFRULE_DENY;
 
 	r->last->endspan = 1;