Improvements (#33)

1. Skip recording undefined variables
2. Parse `in` correctly if it is not imported.
3. base64.decode
4. Handle `with` modifier for qualified data and input.

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

src/builtins/encoding.rs

@@ -0,0 +1,28 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+use crate::ast::Expr;
+use crate::builtins;
+use crate::builtins::utils::{ensure_args_count, ensure_string};
+use crate::lexer::Span;
+use crate::value::Value;
+
+use std::collections::HashMap;
+
+use anyhow::Result;
+use data_encoding::BASE64;
+
+pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
+    m.insert("base64.decode", (base64_decode, 1));
+}
+
+fn base64_decode(span: &Span, params: &[Expr], args: &[Value]) -> Result<Value> {
+    let name = "base64.decode";
+    ensure_args_count(span, name, params, args, 1)?;
+
+    let encoded_str = ensure_string(name, &params[0], &args[0])?;
+    let decoded_bytes = BASE64.decode(encoded_str.as_bytes())?;
+    Ok(Value::String(
+        String::from_utf8_lossy(&decoded_bytes).to_string(),
+    ))
+}