Rename the compile-time configuration variable $HOMEBREWDIR to

$READ_ALLOWED_PATH, allow it to contain more than one directory,
and explain how to use it for NixOS and for GNU Guix Linux.

Feature improvement based on observations, input, and earlier patches
from Lukas Epple <sternenseemann at systemli dot org>, and final
patch also tested by Lukas.

3 files changed, 49 insertions, 12 deletions

diff --git a/configure b/configure
index 1072a305..5f4d0b0d 100755
--- a/configure
+++ b/configure
@@ -107,7 +107,7 @@ BIN_FROM_SBIN=
 INCLUDEDIR=
 LIBDIR=
 MANDIR=
-HOMEBREWDIR=
+READ_ALLOWED_PATH=
 
 WWWPREFIX="/var/www"
 HTDOCDIR=
@@ -461,7 +461,8 @@ echo "#define MANPATH_DEFAULT \"${MANPATH_DEFAULT}\""
 echo "#define OSENUM ${OSENUM}"
 [ -n "${OSNAME}" ] && echo "#define OSNAME \"${OSNAME}\""
 [ -n "${UTF8_LOCALE}" ] && echo "#define UTF8_LOCALE \"${UTF8_LOCALE}\""
-[ -n "${HOMEBREWDIR}" ] && echo "#define HOMEBREWDIR \"${HOMEBREWDIR}\""
+[ -n "${READ_ALLOWED_PATH}" ] \
+	&& echo "#define READ_ALLOWED_PATH \"${READ_ALLOWED_PATH}\""
 [ ${HAVE_ATTRIBUTE} -eq 0 ] && echo "#define __attribute__(x)"
 [ ${HAVE_EFTYPE} -eq 0 ] && echo "#define EFTYPE EINVAL"
 [ ${HAVE_O_DIRECTORY} -eq 0 ] && echo "#define O_DIRECTORY 0"
diff --git a/configure.local.example b/configure.local.example
index 95759f61..5f0e3654 100644
--- a/configure.local.example
+++ b/configure.local.example
@@ -209,14 +209,28 @@ INSTALL_LIB="${INSTALL} -m 0444"
 INSTALL_MAN="${INSTALL} -m 0444"
 INSTALL_DATA="${INSTALL} -m 0444"
 
-# When using the "homebrew" package manager on Mac OS X, the actual
-# manuals are located in a so-called "cellar" and only symlinked
-# into the manual trees.  To allow mandoc to follow such symlinks,
-# you have to specify the physical location of the cellar as returned
-# by realpath(3), for example:
+# By default, makewhatis(8) can only read from the paths passed on the
+# command line or configured in man.conf(5).
+# But some package managers on some operating systems store manual pages
+# in separate "cellar" or "store" directories and only symlink them
+# into the manual trees.
+# To support one or more such package managers, give makewhatis(8)
+# read access to the cellars and stores on your system, in the form
+# of a colon-separated path:
+
+# Homebrow package manager on Mac OS X:
+PREFIX="/usr/local"
+READ_ALLOWED_PATH="${PREFIX}/Cellar"
+
+# Nix package manager and/or NixOS Linux distribution:
+READ_ALLOWED_PATH="/nix/store"
+
+# GNU Guix package manager and/or GNU Guix Linux distribution:
+READ_ALLOWED_PATH="/gnu/store"
 
+# If multiple package managers are used concurrently:
 PREFIX="/usr/local"
-HOMEBREWDIR="${PREFIX}/Cellar"
+READ_ALLOWED_PATH="/nix/store:${PREFIX}/Cellar"
 
 # --- user settings for the mandoc(3) library --------------------------
 
diff --git a/mandocdb.c b/mandocdb.c
index 1e353bfc..cbbb8f60 100644
--- a/mandocdb.c
+++ b/mandocdb.c
@@ -165,6 +165,9 @@ static	void	 putkey(const struct mpage *, char *, uint64_t);
 static	void	 putkeys(const struct mpage *, char *, size_t, uint64_t);
 static	void	 putmdockey(const struct mpage *,
 			const struct roff_node *, uint64_t, int);
+#ifdef READ_ALLOWED_PATH
+static	int	 read_allowed(const char *);
+#endif
 static	int	 render_string(char **, size_t *);
 static	void	 say(const char *, const char *, ...)
 			__attribute__((__format__ (__printf__, 2, 3)));
@@ -612,8 +615,8 @@ treescan(void)
 				continue;
 			}
 			if (strncmp(buf, basedir, basedir_len) != 0
-#ifdef HOMEBREWDIR
-			    && strncmp(buf, HOMEBREWDIR, strlen(HOMEBREWDIR))
+#ifdef READ_ALLOWED_PATH
+			    && !read_allowed(buf)
 #endif
 			) {
 				if (warnings) say("",
@@ -823,8 +826,8 @@ filescan(const char *infile)
 		start = usefile;
 	else if (strncmp(usefile, basedir, basedir_len) == 0)
 		start = usefile + basedir_len;
-#ifdef HOMEBREWDIR
-	else if (strncmp(usefile, HOMEBREWDIR, strlen(HOMEBREWDIR)) == 0)
+#ifdef READ_ALLOWED_PATH
+	else if (read_allowed(usefile))
 		start = usefile;
 #endif
 	else {
@@ -2381,6 +2384,25 @@ set_basedir(const char *targetdir, int report_baddir)
 	return 1;
 }
 
+#ifdef READ_ALLOWED_PATH
+static int
+read_allowed(const char *candidate)
+{
+	const char	*cp;
+	size_t		 len;
+
+	for (cp = READ_ALLOWED_PATH;; cp += len) {
+		while (*cp == ':')
+			cp++;
+		if (*cp == '\0')
+			return 0;
+		len = strcspn(cp, ":");
+		if (strncmp(candidate, cp, len) == 0)
+			return 1;
+	}
+}
+#endif
+
 static void
 say(const char *file, const char *format, ...)
 {