Improve Mac OS X buggy SH handling.

This allows any content under an SH that is either normal text
or entities to be serialised on the same line as SH instead of
the subsequent line.

Properly call this "headerhack" to point out that this is not
because of lowdown or man(7), but other buggy software.

References #138

nroff.c

@@ -76,6 +76,7 @@ struct	bnode {
 	char				*args; /* (unsafe) 2nd args */
 	int				 close; /* BNODE_COLOUR/FONT */
 	int				 tblhack; /* BSCOPE_SPAN */
+        int				 headerhack; /* BSCOPE_BLOCK */
 	enum bscope			 scope; /* scope */
 	unsigned int			 font; /* if BNODE_FONT */
 #define	BFONT_ITALIC			 0x01
@@ -84,7 +85,6 @@ struct	bnode {
 	unsigned int			 colour; /* if BNODE_COLOUR */
 #define	BFONT_BLUE			 0x01
 #define	BFONT_RED			 0x02
-        int				 trailingspace; /* BSCOPE_BLOCK .SH */
 	TAILQ_ENTRY(bnode)		 entries;
 };
 
@@ -517,8 +517,18 @@ bqueue_flush(const struct nroff *st, struct lowdown_buf *ob,
 				return 0;
 		}
 
-		/* Finally, trailing newline/space. */
-		trailingchar = bn->trailingspace ? ' ' : '\n';
+		/*
+		 * The "headerhack" is used by SH block macros to
+		 * indicate that their children are all normal text or
+		 * entities, and so to output the content on the same
+		 * line as the SH macro.  This is a hack because man(7)
+		 * specifically allows for next-line content; however,
+		 * buggy software (e.g., Mac OS X's makewhatis) don't
+		 * correctly parse empty SH properly.
+		 */
+
+		trailingchar = bn->headerhack ? ' ' : '\n';
+
 		if (nextblk && ob->size > 0 && 
 		    ob->data[ob->size - 1] != trailingchar &&
 		    !hbuf_putc(ob, trailingchar))
@@ -842,7 +852,7 @@ rndr_header(struct nroff *st, struct bnodeq *obq,
 	struct lowdown_buf		*buf = NULL;
 	const struct lowdown_buf	*nbuf;
 	int			 	 rc = 0;
-        const struct lowdown_node	*child = NULL;
+        const struct lowdown_node	*child;
 
 	level = (ssize_t)n->rndr_header.level + st->headers_offs;
 	if (level < 1)
@@ -861,23 +871,24 @@ rndr_header(struct nroff *st, struct bnodeq *obq,
 		if (bn == NULL)
 			return 0;
 
-		if (level == 1
-			&& (child = TAILQ_FIRST(&n->children))
-			&& !TAILQ_NEXT(child, entries)) {
-			/* This is a first-level header and there is exactly one child.
-			 *
-			 * If the child is a `LOWDOWN_NORMAL_TEXT`, put
-			 * a single space between the `.SH` and the
-			 * heading instead of a newline.
-			 *
-			 * This renders headers as (e.g.) `.SH
-			 * SYNOPSIS` instead of `.SH\nSYNOPSIS`, which
-			 * is important for macOS `makewhatis`.
-			 *
-			 * See: https://github.com/kristapsdz/lowdown/pull/138
-			 */
-			bn->trailingspace = child->type == LOWDOWN_NORMAL_TEXT;
+		/*
+		 * Do a scan of the contents of the SH.  If there's only
+		 * normal text (or entities), then record this fact.  It
+		 * will be used in bqueue_flush() for how the macro is
+		 * serialised.
+		 */
+
+		if (level == 1) {
+			bn->headerhack = 1;
+			TAILQ_FOREACH(child, &n->children, entries) {
+				if (child->type == LOWDOWN_ENTITY ||
+				    child->type == LOWDOWN_NORMAL_TEXT)
+					continue;
+				bn->headerhack = 0;
+				break;
+			}
 		}
+
 		TAILQ_CONCAT(obq, bq, entries);
 		st->post_para = 1;
 		return 1;

regress/header-buggy-makewhatis.man

@@ -0,0 +1,22 @@
+.SH Same line as SH.
+.LP
+a
+.SS
+Not same line as SS.
+.LP
+b
+.SH Same \(lqline\(rq.
+.LP
+c
+.SH
+Not same \fBline\fR <\fIfoo.com\fR>
+.LP
+d
+.SH
+Not same \fIline\fR.
+.LP
+e
+.SH
+Not same \fBline\fR.
+.LP
+e

regress/header-buggy-makewhatis.md

@@ -0,0 +1,12 @@
+# Same line as SH.
+a
+## Not same line as SS.
+b
+# Same "line".
+c
+# Not same [line](foo.com)
+d
+# Not same *line*.
+e
+# Not same **line**.
+e