Add max input POD check to MainPodBuilder (#440)

src/frontend/error.rs

@@ -35,6 +35,8 @@ pub enum InnerError {
     PodlangParse(String),
     #[error("POD Request validation error: {0}")]
     PodRequestValidation(String),
+    #[error("Too many input PODs provided: {0} were provided, but the maximum is {1}")]
+    TooManyInputPods(usize, usize),
     #[error("Too many public statements provided: {0} were provided, but the maximum is {1}")]
     TooManyPublicStatements(usize, usize),
     #[error("Too many statements provided: {0} were provided, but the maximum is {1}")]
@@ -108,6 +110,9 @@ impl Error {
     pub(crate) fn pod_request_validation(e: String) -> Self {
         new!(PodRequestValidation(e))
     }
+    pub(crate) fn too_many_input_pods(found: usize, max: usize) -> Self {
+        new!(TooManyInputPods(found, max))
+    }
     pub(crate) fn too_many_public_statements(found: usize, max: usize) -> Self {
         new!(TooManyPublicStatements(found, max))
     }

src/frontend/mod.rs

@@ -164,8 +164,15 @@ impl MainPodBuilder {
             dict_contains: Vec::new(),
         }
     }
-    pub fn add_pod(&mut self, pod: MainPod) {
+    pub fn add_pod(&mut self, pod: MainPod) -> Result<()> {
         self.input_pods.push(pod);
+        match self.input_pods.len() > self.params.max_input_pods {
+            true => Err(Error::too_many_input_pods(
+                self.input_pods.len(),
+                self.params.max_input_pods,
+            )),
+            _ => Ok(()),
+        }
     }
     pub fn insert(&mut self, public: bool, st_op: (Statement, Operation)) -> Result<()> {
         // TODO: Do error handling instead of panic