From e0cce79cf40ca89ded697a27af804355ef9512a3 Mon Sep 17 00:00:00 2001
From: Simon Tatham <anakin@pobox.com>
Date: Tue, 12 Apr 2005 08:38:28 +0000
Subject: input.c was capable of generating a paragraph structure with no text
 in it, if the input paragraph contained (say) an unrecognised control command
 and nothing else. Such paragraphs can confuse back ends later on, so input.c
 should refrain from generating them. Added a check and a polite error message
 (just in case the user manages to generate an empty paragraph using otherwise
 legal syntax).

[originally from svn r5629]
---
 error.c   |  5 +++++
 halibut.h |  1 +
 input.c   | 14 +++++++++++++-
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/error.c b/error.c
index 3635f0f..b1e74a1 100644
--- a/error.c
+++ b/error.c
@@ -278,6 +278,11 @@ static void do_error(int code, va_list ap) {
 	flags = FILEPOS;
 	sfree(sp);
 	break;
+      case err_emptypara:
+	fpos = *va_arg(ap, filepos *);
+	sprintf(error, "found no text in paragraph");
+	flags = FILEPOS;
+	break;
       case err_whatever:
 	sp = va_arg(ap, char *);
         vsprintf(error, sp, ap);
diff --git a/halibut.h b/halibut.h
index ed2a0da..99b9a0e 100644
--- a/halibut.h
+++ b/halibut.h
@@ -244,6 +244,7 @@ enum {
     err_text_codeline,		       /* \c line too long in text backend */
     err_htmlver,		       /* unrecognised HTML version keyword */
     err_charset,		       /* unrecognised character set name */
+    err_emptypara,		       /* paragraph contains no actual text */
     err_whatever                       /* random error of another type */
 };
 
diff --git a/input.c b/input.c
index 493449c..d8d44f9 100644
--- a/input.c
+++ b/input.c
@@ -1529,7 +1529,19 @@ static void read_file(paragraph ***ret, input *in, indexdata *idx,
 	}
 	stk_free(parsestk);
 	prev_para_type = par.type;
-	addpara(par, ret);
+	/*
+	 * Before we add the paragraph to the output list, we
+	 * should check that there was any text in it at all; there
+	 * might not be if (for example) the paragraph contained
+	 * nothing but an unrecognised command sequence, and if we
+	 * put an empty paragraph on the list it may confuse the
+	 * back ends later on.
+	 */
+	if (par.words) {
+	    addpara(par, ret);
+	} else {
+	    error(err_emptypara, &par.fpos);
+	}
 	if (t.type == tok_eof)
 	    already = TRUE;
     }
-- 
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