vcc: do not overwrite SUB symbol properties when call'ing

vcc_act_call() implements use-before-define semantics. To do so, it
needs to instantiate SUB symbols if they do not exist.

However, it wrongly called VCC_GlobalSymbol() also for existing
symbols, overwriting symbol properties.

In the case of the built-in subs, the symbol's lname (historically)
still is the unescaped literal name, while user defined subs have
their name escaped via VCC_GlobalSymbol() -> VCC_PrintCName().

This made the wrong call to VCC_GlobalSymbol() apparent when a
built-in sub was called with an explicit "call" action.

Besides fixing the VCC_GlobalSymbol() call, we also need to set the
lname and rname attributes for built-in SUB symbols initialized in
VCC_New().

Alternatively, we could also have used VCC_GlobalSymbol() there, but
that would have affected other places where we (still) rely on the
known name scheme of built-in subs, e.h. EmitStruct(). While the name
unifaction was nice in general, I found the necessary changes (look up
SUB symbols) not worth the benefit.

Fixes #3719

bin/varnishtest/tests/m00053.vtc

@@ -92,9 +92,12 @@ varnish v1 -vcl {
 	sub vcl_backend_fetch {
 		debug.call(priv_top);
 	}
+	sub vcl_backend_response {
+		set beresp.status = 200;
+	}
 	sub vcl_backend_error {
 		# falling through to None backend would be success
-		set beresp.status = 200;
+		call vcl_backend_response;
 		return (deliver);
 	}
 } -start

lib/libvcc/vcc_action.c

@@ -52,16 +52,16 @@ vcc_act_call(struct vcc *tl, struct token *t, struct symbol *sym)
 	t0 = tl->t;
 	sym = VCC_SymbolGet(tl, SYM_MAIN, SYM_NONE, SYMTAB_PARTIAL_NOERR,
 	    XREF_REF);
-	if (sym == NULL)
+	if (sym == NULL) {
 		sym = VCC_SymbolGet(tl, SYM_MAIN, SYM_SUB, SYMTAB_CREATE,
 		    XREF_REF);
-
-	if (sym == NULL)
-		return;
+		if (sym == NULL)
+			return;
+		VCC_GlobalSymbol(sym, SUB);
+	}
 
 	if (sym->kind == SYM_SUB) {
 		vcc_AddCall(tl, t0, sym);
-		VCC_GlobalSymbol(sym, SUB);
 
 		Fb(tl, 1, "%s(ctx, VSUB_STATIC, NULL);\n", sym->lname);
 		SkipToken(tl, ';');

lib/libvcc/vcc_compile.c

@@ -820,6 +820,7 @@ VCC_New(void)
 	struct vcc *tl;
 	struct symbol *sym;
 	struct proc *p;
+	struct vsb *vsb;
 	int i;
 
 	ALLOC_OBJ(tl, VCC_MAGIC);
@@ -849,7 +850,25 @@ VCC_New(void)
 		    SYM_MAIN, SYM_SUB, VCL_LOW, VCL_HIGH);
 		p = vcc_NewProc(tl, sym);
 		p->method = &method_tab[i];
-		VSB_printf(p->cname, "VGC_function_%s", p->method->name);
+
+		// see also VCC_GlobalSymbol()
+		vsb = VSB_new_auto();
+		AN(vsb);
+		VSB_printf(vsb, "%s_%s", SUB->global_pfx, p->method->name);
+		AZ(VSB_finish(vsb));
+
+		AZ(VSB_bcat(p->cname, VSB_data(vsb), VSB_len(vsb)));
+
+		sym->lname = strdup(VSB_data(vsb));
+		AN(sym->lname);
+
+		VSB_clear(vsb);
+		VSB_printf(vsb, "sub_%s", sym->lname);
+		AZ(VSB_finish(vsb));
+
+		sym->rname = strdup(VSB_data(vsb));
+		AN(sym->rname);
+		VSB_destroy(&vsb);
 	}
 	tl->sb = VSB_new_auto();
 	AN(tl->sb);