fix: prevent panic for issues #4474 and #4317 (#4538)

Co-authored-by: Maximilian Roos <[email protected]>

CHANGELOG.md

@@ -19,6 +19,7 @@
 **Fixes**:
 
 - Support expressions on left hand side of `std.in` operator. (@kgutwin, #4498)
+- Prevent panic for `from {}` and `std` (@m-span, #4538)
 
 **Documentation**:
 

prqlc/prqlc/src/semantic/lowering.rs

@@ -227,7 +227,10 @@ impl Lowerer {
             pl::ExprKind::Ident(fq_table_name) => {
                 // ident that refer to table: create an instance of the table
                 let id = expr.id.unwrap();
-                let tid = *self.table_mapping.get(&fq_table_name).unwrap();
+                let tid = *self
+                    .table_mapping
+                    .get(&fq_table_name)
+                    .ok_or_else(|| Error::new_bug(4474))?;
 
                 log::debug!("lowering an instance of table {fq_table_name} (id={id})...");
 

prqlc/prqlc/src/semantic/resolver/functions.rs

@@ -273,7 +273,10 @@ impl Resolver<'_> {
 
                 // add relation frame into scope
                 if partial_application_position.is_none() {
-                    let frame = arg.lineage.as_ref().unwrap();
+                    let frame = arg
+                        .lineage
+                        .as_ref()
+                        .ok_or_else(|| Error::new_bug(4317).with_span(closure.body.span))?;
                     if is_last {
                         self.root_mod.module.insert_frame(frame, NS_THIS);
                     } else {

prqlc/prqlc/tests/integration/bad_error_messages.rs

@@ -213,3 +213,40 @@ fn a_arrow_b() {
     Error: internal compiler error; tracked at https://github.com/PRQL/prql/issues/4280
     "###);
 }
+
+#[test]
+fn just_std() {
+    assert_snapshot!(compile(r###"
+    std
+    "###).unwrap_err(), @r###"
+    Error:
+       ╭─[:2:5]
+       │
+     2 │     std
+       │     ──┬─
+       │       ╰─── internal compiler error; tracked at https://github.com/PRQL/prql/issues/4474
+    ───╯
+    "###);
+}
+
+#[test]
+fn empty_tuple_from() {
+    assert_snapshot!(compile(r###"
+    from {}
+    "###).unwrap_err(), @r###"
+    Error: internal compiler error; tracked at https://github.com/PRQL/prql/issues/4317
+    "###);
+
+    assert_snapshot!(compile(r###"
+    from []
+    "###).unwrap_err(), @r###"
+    Error: internal compiler error; tracked at https://github.com/PRQL/prql/issues/4317
+    "###);
+
+    assert_snapshot!(compile(r###"
+    from {}
+    select a
+    "###).unwrap_err(), @r###"
+    Error: internal compiler error; tracked at https://github.com/PRQL/prql/issues/4317
+    "###);
+}