Merge remote-tracking branch 'origin/topic/jsiwek/const'

* origin/topic/jsiwek/const:
  Make const variables actually constant.  Addresses #922.

Closes #922.

testing/btest/Baseline/language.const/invalid.stderr

@@ -0,0 +1,13 @@
+error in ./invalid.bro, line 15: const is not a modifiable lvalue (foo)
+error in ./invalid.bro, line 16: const is not a modifiable lvalue (foo)
+error in ./invalid.bro, line 17: const is not a modifiable lvalue (bar)
+error in ./invalid.bro, line 17: const is not a modifiable lvalue (foo)
+error in ./invalid.bro, line 18: const is not a modifiable lvalue (foo)
+error in ./invalid.bro, line 19: const is not a modifiable lvalue (foo)
+error in ./invalid.bro, line 20: const is not a modifiable lvalue (foo)
+error in ./invalid.bro, line 22: const is not a modifiable lvalue (foo)
+error in ./invalid.bro, line 25: const is not a modifiable lvalue (bar)
+error in ./invalid.bro, line 26: const is not a modifiable lvalue (baz)
+error in ./invalid.bro, line 27: const is not a modifiable lvalue (bar)
+error in ./invalid.bro, line 28: const is not a modifiable lvalue (baz)
+error in ./invalid.bro, line 33: const is not a modifiable lvalue (foo)

testing/btest/Baseline/language.const/valid.stdout

@@ -0,0 +1,10 @@
+40
+enter f, 10
+exit f, 110
+enter f, 9
+exit f, 109
+enter f, 7
+exit f, 107
+foo, 10
+bar, 9
+baz, 7

testing/btest/language/const.bro

@@ -0,0 +1,79 @@
+# @TEST-EXEC: bro -b valid.bro 2>valid.stderr 1>valid.stdout
+# @TEST-EXEC: btest-diff valid.stderr
+# @TEST-EXEC: btest-diff valid.stdout
+
+# @TEST-EXEC-FAIL: bro -b invalid.bro 2>invalid.stderr 1>invalid.stdout
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff invalid.stderr
+# @TEST-EXEC: btest-diff invalid.stdout
+
+@TEST-START-FILE valid.bro
+# First some simple code that should be valid and error-free.
+
+function f(c: count)
+	{
+	print "enter f", c;
+	c = c + 100;
+	print "exit f", c;
+	}
+
+const foo = 0 &redef;
+redef foo = 10;
+
+const bar = 9;
+
+event bro_init()
+	{
+	const baz = 7;
+	local i = foo;
+	i = i + bar + 2;
+	i = i + baz + 11;
+	++i;
+	print i;
+	--i;
+	f(foo);
+	f(bar);
+	f(baz);
+	print "foo", foo;
+	print "bar", bar;
+	print "baz", baz;
+	}
+
+@TEST-END-FILE
+
+@TEST-START-FILE invalid.bro
+# Now some const assignments that should generate errors at parse-time.
+
+const foo = 0 &redef;
+redef foo = 10;
+
+const bar = 9;
+
+event bro_init()
+	{
+	const baz = 7;
+	local s = 0;
+
+	print "nope";
+
+	foo = 100;
+	foo = bar;
+	foo = bar = baz;
+	foo = s;
+	++foo;
+	s = foo = bar;
+
+	if ( foo = 0 )
+		print "nope";
+
+	bar = 1 + 1;
+	baz = s;
+	++bar;
+	--baz;
+
+	print "foo", foo;
+	print "bar", bar;
+	print "baz", baz;
+	print "foo=foo", foo = foo;
+	}
+
+@TEST-END-FILE