Add PCRE support

Closes #1137

INSTALL.adoc

@@ -193,6 +193,8 @@ configure script and building documentation:
 |Tool				|Description
 |readline			|Adds support for completion and history in
 				 search and command prompts.
+|PCRE				|Adds support for Perl Compatible Regular
+				 Expressions in searches.
 |autoconf			|Contains autoreconf for generating configure
 				 from configure.ac.
 |asciidoc (>= 8.4)		|Generates HTML and (DocBook) XML from text.

configure.ac

@@ -36,12 +36,33 @@ AX_LIB_READLINE(6.3)
 
 AM_ICONV
 
+dnl Check for PCRE (Perl Compatible Regular Expressions) library
+AC_ARG_WITH(pcre, [AS_HELP_STRING([--without-pcre], [do not use PCRE (Perl Compatible Regular Expressions) library])])
+AS_IF([test "x$with_pcre" != xno], [
+	AC_CHECK_HEADERS([pcre2posix.h])
+	AS_IF([test "x$ac_cv_header_pcre2posix_h" = xyes], [
+		AC_CHECK_LIB([pcre2-posix], [regexec], [
+			AC_DEFINE([HAVE_PCRE2], [1], [Define if you have PCRE2])
+			LIBS="$LIBS -lpcre2-posix -lpcre2-8"
+		])
+	])
+	AS_IF([test "x$ac_cv_lib_pcre2_posix_regexec" != xyes], [
+		AC_CHECK_HEADERS([pcreposix.h])
+		AS_IF([test "x$ac_cv_header_pcreposix_h" = xyes], [
+			AC_CHECK_LIB([pcreposix], [regexec], [
+				AC_DEFINE([HAVE_PCRE], [1], [Define if you have PCRE])
+				LIBS="$LIBS -lpcreposix -lpcre"
+			])
+		])
+	])
+])
+
 dnl OS-specific
 case $(uname -s 2>/dev/null || echo unknown) in "OS400")
 	AC_CHECK_LIB(util, main, [LIBS="$LIBS -lutil"], AC_MSG_ERROR([Please install the libutil-devel package]))
 	;;
 esac
-    
+
 AC_CHECK_PROGS(SED, [gsed], [sed])
 AC_TDD_GCOV
 AC_SUBST(COVERAGE_CFLAGS)

include/tig/tig.h

@@ -56,7 +56,13 @@
 #include <libgen.h>
 #include <termios.h>
 
+#if defined HAVE_PCRE2
+#include <pcre2posix.h>
+#elif defined HAVE_PCRE
+#include <pcreposix.h>
+#else
 #include <regex.h>
+#endif
 
 #include <locale.h>
 #include <langinfo.h>

src/search.c

@@ -67,15 +67,17 @@ setup_and_find_next(struct view *view, enum request request)
 	    && !utf8_string_contains_uppercase(view->env->search))
 		regex_flags |= REG_ICASE;
 
-	if (view->regex) {
-		regfree(view->regex);
-		*view->grep = 0;
-	} else {
+	if (!view->regex) {
 		view->regex = calloc(1, sizeof(*view->regex));
 		if (!view->regex)
 			return ERROR_OUT_OF_MEMORY;
 	}
 
+	if (*view->grep) {
+		regfree(view->regex);
+		*view->grep = 0;
+	}
+
 	regex_err = regcomp(view->regex, view->env->search, REG_EXTENDED | regex_flags);
 	if (regex_err != 0) {
 		char buf[SIZEOF_STR] = "unknown error";