Add std.syntax() to check if we run at a certain VCL level

bin/varnishtest/tests/m00001.vtc

@@ -5,12 +5,15 @@ server s1 {
 	txresp -hdr "foo: bAr" -hdr "bar: fOo" -bodylen 4
 } -start
 
-varnish v1 -vcl+backend {
+varnish v1 -syntax 4.1 -vcl+backend {
 	import std;
 
 	sub vcl_deliver {
 		set resp.http.foo = std.toupper(resp.http.foo);
 		set resp.http.bar = std.tolower(resp.http.bar);
+		set resp.http.vcl40 = std.syntax(4.0);
+		set resp.http.vcl41 = std.syntax(4.1);
+		set resp.http.vcl42 = std.syntax(4.2);
 		std.set_ip_tos(32);
 	}
 } -start
@@ -24,9 +27,19 @@ client c1 {
 	expect resp.bodylen == "4"
 	expect resp.http.foo == "BAR"
 	expect resp.http.bar == "foo"
+	expect resp.http.vcl40 == "true"
+	expect resp.http.vcl41 == "true"
+	expect resp.http.vcl42 == "false"
 } -run
 
-varnish v1 -vcl+backend {
+varnish v1 -syntax 4.0 -vcl+backend {
+	import std;
+
+	sub vcl_deliver {
+		set resp.http.vcl40 = std.syntax(4.0);
+		set resp.http.vcl41 = std.syntax(4.1);
+		set resp.http.vcl42 = std.syntax(4.2);
+	}
 }
 
 client c1 {
@@ -36,14 +49,20 @@ client c1 {
 	expect resp.bodylen == "4"
 	expect resp.http.foo == "bAr"
 	expect resp.http.bar == "fOo"
+	expect resp.http.vcl40 == "true"
+	expect resp.http.vcl41 == "false"
+	expect resp.http.vcl42 == "false"
 } -run
 
+varnish v1 -vcl+backend { }
+
 varnish v1 -cliok "debug.vmod"
 varnish v1 -cliok "vcl.list"
 
 varnish v1 -expect vmods == 1
 
 varnish v1 -cliok "vcl.discard vcl1"
+varnish v1 -cliok "vcl.discard vcl2"
 varnish v1 -cliok "vcl.list"
 varnish v1 -cliok "debug.vmod"
 

lib/libvmod_std/vmod.vcc

@@ -338,6 +338,11 @@ Example
 	|	...
 	| }
 
+$Function BOOL issyntax(REAL)
+
+Description
+	Returns the true if VCL version is at least REAL.
+
 SEE ALSO
 ========
 

lib/libvmod_std/vmod_std.c

@@ -285,3 +285,17 @@ vmod_late_100_continue(VRT_CTX, VCL_BOOL late)
 	if (ctx->req->want100cont)
 		ctx->req->late100cont = late;
 }
+
+VCL_BOOL v_matchproto_(td_std_syntax)
+vmod_syntax(VRT_CTX, VCL_REAL r)
+{
+
+	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
+	assert(ctx->syntax == 40 || ctx->syntax == 41);
+	/*
+	 * We need to be careful because non-integer numbers have imprecise
+	 * IEE754 represenation (4.1 is 0x1.0666666666666p+2 = 4.09999...)
+	 * By scaling up and rounding, this is taken care of.
+	 */
+	return (round(r * 10) <= ctx->syntax);
+}