Merge pull request #2574 from rtfeldman/fix-panic-on-unimported-module

[Bug] Handle unimported modules properly

compiler/can/src/annotation.rs

@@ -130,7 +130,9 @@ fn make_apply_symbol(
                 // it was imported but it doesn't expose this ident.
                 env.problem(roc_problem::can::Problem::RuntimeError(problem));
 
-                Err(Type::Erroneous(Problem::UnrecognizedIdent((*ident).into())))
+                // A failed import should have already been reported through
+                // roc_can::env::Env::qualified_lookup's checks
+                Err(Type::Erroneous(Problem::SolvedTypeError))
             }
         }
     }

compiler/can/src/env.rs

@@ -124,12 +124,17 @@ impl<'a> Env<'a> {
                                 })
                             }
                         },
-                        None => {
-                            panic!(
-                                "Module {} exists, but is not recorded in dep_idents",
-                                module_name
-                            )
-                        }
+                        None => Err(RuntimeError::ModuleNotImported {
+                            module_name,
+                            imported_modules: self
+                                .dep_idents
+                                .keys()
+                                .filter_map(|module_id| self.module_ids.get_name(*module_id))
+                                .map(|module_name| module_name.as_ref().into())
+                                .collect(),
+                            region,
+                            module_exists: true,
+                        }),
                     }
                 }
             }
@@ -141,6 +146,7 @@ impl<'a> Env<'a> {
                     .map(|string| string.as_ref().into())
                     .collect(),
                 region,
+                module_exists: false,
             }),
         }
     }

compiler/problem/src/can.rs

@@ -171,10 +171,37 @@ pub enum RuntimeError {
         region: Region,
         exposed_values: Vec<Lowercase>,
     },
+    /// A module was referenced, but hasn't been imported anywhere in the program
+    ///
+    /// An example would be:
+    /// ```roc
+    /// app "hello"
+    ///     packages { pf: "platform" }
+    ///     imports [ pf.Stdout]
+    ///     provides [ main ] to pf
+    ///
+    /// main : Task.Task {} [] // Task isn't imported!
+    /// main = Stdout.line "I'm a Roc application!"
+    /// ```
     ModuleNotImported {
+        /// The name of the module that was referenced
         module_name: ModuleName,
+        /// A list of modules which *have* been imported
         imported_modules: MutSet<Box<str>>,
+        /// Where the problem occurred
         region: Region,
+        /// Whether or not the module exists at all
+        ///
+        /// This is used to suggest that the user import the module, as opposed to fix a
+        /// typo in the spelling.  For example, if the user typed `Task`, and the platform
+        /// exposes a `Task` module that hasn't been imported, we can sugguest that they
+        /// add the import statement.
+        ///
+        /// On the other hand, if the user typed `Tesk`, they might want to check their
+        /// spelling.
+        ///
+        /// If unsure, this should be set to `false`
+        module_exists: bool,
     },
     InvalidPrecedence(PrecedenceProblem, Region),
     MalformedIdentifier(Box<str>, roc_parse::ident::BadIdent, Region),