utils: Introduce packages.zeek with can_load() helper

scripts/base/init-default.zeek

@@ -17,6 +17,7 @@
 @load base/utils/geoip-distance
 @load base/utils/hash_hrw
 @load base/utils/numbers
+@load base/utils/packages
 @load base/utils/paths
 @load base/utils/patterns
 @load base/utils/queue

scripts/base/utils/packages.zeek

@@ -0,0 +1,16 @@
+##! Rudimentary functions for helping with Zeek packages.
+
+## Checks whether @load of a given package name could
+## be successful.
+##
+## This tests for the existence of corresponding script files
+## in ZEEKPATH. It does not attempt to parse and validate
+## any actual Zeek script code.
+##
+## path: The filename, package or path to test.
+##
+## Returns: T if the given filename, package or path may load.
+function can_load(p: string): bool
+	{
+	return find_in_zeekpath(p) != "";
+	}

testing/btest/Baseline/coverage.default-load-baseline/canonified_loaded_scripts.log

@@ -290,6 +290,7 @@ scripts/base/init-default.zeek
   scripts/base/utils/files.zeek
   scripts/base/utils/geoip-distance.zeek
   scripts/base/utils/numbers.zeek
+  scripts/base/utils/packages.zeek
   scripts/base/utils/queue.zeek
   scripts/base/utils/strings.zeek
   scripts/base/utils/thresholds.zeek

testing/btest/Baseline/scripts.base.utils.packages/output

@@ -0,0 +1,4 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+no pkg3
+pkg1!
+pkg2!

testing/btest/scripts/base/utils/packages.zeek

@@ -0,0 +1,32 @@
+# @TEST-EXEC: zeek -b %INPUT >output
+# @TEST-EXEC: btest-diff output
+
+@load base/utils/packages
+
+@if ( can_load("pkg1") )
+@load pkg1
+@endif
+
+@if ( can_load("pkg2") )
+@load pkg2
+@endif
+
+@if ( can_load("pkg3") )
+@load pkg3
+@else
+print "no pkg3";
+@endif
+
+@TEST-START-FILE pkg1.zeek
+event zeek_init()
+	{
+	print "pkg1!";
+	}
+@TEST-END-FILE
+
+@TEST-START-FILE pkg2/__load__.zeek
+event zeek_init()
+	{
+	print "pkg2!";
+	}
+@TEST-END-FILE