Arity for builtins (#28)

Old-style function call

Utility for running opa yaml tests

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

src/utils.rs

@@ -0,0 +1,59 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+use crate::ast::*;
+use crate::builtins::*;
+
+use std::collections::HashMap;
+
+use anyhow::{bail, Result};
+
+pub fn get_path_string(refr: &Expr, document: Option<&str>) -> Result<String> {
+    let mut comps = vec![];
+    let mut expr = Some(refr);
+    while expr.is_some() {
+        match expr {
+            Some(Expr::RefDot { refr, field, .. }) => {
+                comps.push(field.text());
+                expr = Some(refr);
+            }
+            Some(Expr::RefBrack { refr, index, .. })
+                if matches!(index.as_ref(), Expr::String(_)) =>
+            {
+                if let Expr::String(s) = index.as_ref() {
+                    comps.push(s.text());
+                    expr = Some(refr);
+                }
+            }
+            Some(Expr::Var(v)) => {
+                comps.push(v.text());
+                expr = None;
+            }
+            _ => bail!("internal error: not a simple ref"),
+        }
+    }
+    if let Some(d) = document {
+        comps.push(d);
+    };
+    comps.reverse();
+    Ok(comps.join("."))
+}
+
+pub fn get_extra_arg<'a>(expr: &'a Expr, arities: &HashMap<String, u8>) -> Option<&'a Expr<'a>> {
+    if let Expr::Call { fcn, params, .. } = expr {
+        if let Ok(path) = get_path_string(fcn, None) {
+            let n_args = if let Some(n_args) = arities.get(&path) {
+                *n_args
+            } else if let Some((_, n_args)) = BUILTINS.get(path.as_str()) {
+                *n_args
+            } else {
+                return None;
+            };
+            if n_args as usize == params.len() - 1 {
+                return params.last();
+            }
+        }
+    }
+
+    None
+}