Add function to get prototype for builtin

This is needed for the hover functionality in the vscode extension.

Signed-off-by: Sean Young <sean@mess.org>

src/sema/builtin.rs

@@ -7,7 +7,7 @@ use num_bigint::BigInt;
 use num_traits::One;
 use parser::pt;
 
-struct Prototype {
+pub struct Prototype {
     pub builtin: Builtin,
     pub namespace: Option<&'static str>,
     pub name: &'static str,
@@ -358,6 +358,20 @@ pub fn is_builtin_call(namespace: Option<&str>, fname: &str, ns: &Namespace) ->
     })
 }
 
+/// Get the prototype for a builtin. If the prototype has arguments, it is a function else
+/// it is a variable.
+pub fn get_prototype(builtin: Builtin) -> &'static Prototype {
+    if let Some(p) = BUILTIN_FUNCTIONS.iter().find(|p| p.builtin == builtin) {
+        return p;
+    }
+
+    if let Some(p) = BUILTIN_VARIABLE.iter().find(|p| p.builtin == builtin) {
+        return p;
+    }
+
+    panic!("cannot find prototype for {:?}", builtin);
+}
+
 /// Does variable name match builtin
 pub fn builtin_var(
     loc: &pt::Loc,

tests/builtins.rs

@@ -0,0 +1,13 @@
+extern crate solang;
+
+use solang::sema::ast;
+use solang::sema::builtin;
+
+#[test]
+fn builtin_prototype() {
+    let p = builtin::get_prototype(ast::Builtin::Timestamp);
+
+    assert_eq!(p.namespace, Some("block"));
+    assert_eq!(p.name, "timestamp");
+    assert!(p.args.is_empty());
+}