Error when platform package config cannot be found

This avoid compiler hangs that occurred before

Closes #1822

compiler/load/src/file.rs

@@ -1217,6 +1217,10 @@ impl<'a> LoadStart<'a> {
                     let buf = to_parse_problem_report(problem, module_ids, root_exposed_ident_ids);
                     return Err(LoadingProblem::FormattedReport(buf));
                 }
+                Err(LoadingProblem::FileProblem { filename, error }) => {
+                    let buf = to_file_problem_report(&filename, error);
+                    return Err(LoadingProblem::FormattedReport(buf));
+                }
                 Err(e) => return Err(e),
             }
         };
@@ -1367,7 +1371,7 @@ where
 
     // We need to allocate worker *queues* on the main thread and then move them
     // into the worker threads, because those workers' stealers need to be
-    // shared bet,een all threads, and this coordination work is much easier
+    // shared between all threads, and this coordination work is much easier
     // on the main thread.
     let mut worker_queues = bumpalo::collections::Vec::with_capacity_in(num_workers, arena);
     let mut stealers = bumpalo::collections::Vec::with_capacity_in(num_workers, arena);
@@ -1745,7 +1749,7 @@ fn update<'a>(
                 state.module_cache.module_names.insert(*id, name.clone());
             }
 
-            // This was a dependency. Write it down and keep processing messaages.
+            // This was a dependency. Write it down and keep processing messages.
             let mut exposed_symbols: MutSet<Symbol> =
                 HashSet::with_capacity_and_hasher(header.exposes.len(), default_hasher());
 
@@ -2638,7 +2642,10 @@ fn parse_header<'a>(
                                 Msg::Many(vec![app_module_header_msg, load_pkg_config_msg]),
                             ))
                         } else {
-                            Ok((module_id, app_module_header_msg))
+                            Err(LoadingProblem::FileProblem {
+                                filename: pkg_config_roc,
+                                error: io::ErrorKind::NotFound.into(),
+                            })
                         }
                     } else {
                         panic!("could not find base")

compiler/load/tests/fixtures/build/app_with_deps/Primary.roc

@@ -1,7 +1,6 @@
-app "primary"
+interface Primary
-    packages { blah: "./blah" }
+    exposes [ blah2, blah3, str, alwaysThree, identity, z, w, succeed, withDefault, yay ]
     imports [ Dep1, Dep2.{ two, foo }, Dep3.Blah.{ bar }, Res ]
-    provides [ blah2, blah3, str, alwaysThree, identity, z, w, succeed, withDefault, yay ] to blah
 
 blah2 = Dep2.two
 blah3 = bar

compiler/load/tests/test_load.rs

@@ -82,11 +82,6 @@ mod test_load {
         let app_module = files.pop().unwrap();
         let interfaces = files;
 
-        debug_assert!(
-            app_module.1.starts_with("app"),
-            "The final module should be the application module"
-        );
-
         for (name, source) in interfaces {
             let mut filename = PathBuf::from(name);
             filename.set_extension("roc");
@@ -278,15 +273,10 @@ mod test_load {
                 "Main",
                 indoc!(
                     r#"
-                        app "test-app"
+                        interface Other exposes [ empty ] imports [ RBTree ]
-                            packages { blah: "./blah" }
-                            imports [ RBTree ]
-                            provides [ main ] to blah
 
                         empty : RBTree.RedBlackTree I64 I64
                         empty = RBTree.empty
-
-                        main = empty
                     "#
                 ),
             ),
@@ -530,7 +520,7 @@ mod test_load {
             "Main",
             indoc!(
                 r#"
-                        app "test-app" packages { blah: "./blah" } provides [ main ] to blah
+                interface Main exposes [ main ] imports []
 
                 main = [
                 "#
@@ -561,9 +551,7 @@ mod test_load {
     }
 
     #[test]
-    #[should_panic(
+    #[should_panic(expected = "FILE NOT FOUND")]
-        expected = "FileProblem { filename: \"tests/fixtures/build/interface_with_deps/invalid$name.roc\", error: NotFound }"
-    )]
     fn file_not_found() {
         let subs_by_module = MutMap::default();
         let loaded_module = load_fixture("interface_with_deps", "invalid$name", subs_by_module);
@@ -589,4 +577,29 @@ mod test_load {
             },
         );
     }
+
+    #[test]
+    fn platform_does_not_exist() {
+        let modules = vec![(
+            "Main",
+            indoc!(
+                r#"
+                app "example"
+                    packages { pf: "./zzz-does-not-exist" }
+                    imports [ ]
+                    provides [ main ] to pf
+
+                main = ""
+                "#
+            ),
+        )];
+
+        match multiple_modules(modules) {
+            Err(report) => {
+                assert!(report.contains("FILE NOT FOUND"));
+                assert!(report.contains("zzz-does-not-exist/Package-Config.roc"));
+            }
+            Ok(_) => unreachable!("we expect failure here"),
+        }
+    }
 }