Check for missing fields in object literals (#2332)

fixes #2331

Changelog.md

@@ -4,6 +4,9 @@
   `x.vals()` is introduced. It works like `x.bytes()`, but returns the elements
   as type `Nat8`.
 
+* Bugfix: Certain ill-typed object literals are now prevented by the type
+  checker.
+
 == 0.5.7 (2021-02-05)
 
 * The type checker now exploits the expected type, if any,

src/lang_utils/error_codes.ml

@@ -154,4 +154,5 @@ let error_codes : (string * string option) list =
     "M0148", None; (* Block syntax is deprecated in this position *)
     "M0149", Some([%blob "error_codes/M0149.adoc"]); (* Expected mutable 'var' field, found immutable field *)
     "M0150", Some([%blob "error_codes/M0150.adoc"]); (* Expected immutable field, found mutable 'var' field *)
+    "M0151", Some([%blob "error_codes/M0151.adoc"]); (* missing field in object literal *)
   ]

src/lang_utils/error_codes/M0151.adoc

@@ -0,0 +1,18 @@
+= M0151
+
+This error means that a object literal is missing some fields, maybe because of a typo.
+
+Erroneous code examples:
+
+```
+  { first_name = "Fred" } : { firstName : Text }
+  { firstName = "Fred" } : { firstName : Text; lastName : Text }
+```
+
+If you encounter this error, you need to add the missing field name to the
+object literal.
+
+```
+  { firstName = "Fred" } : { firstName : Text }
+  { firstName = "Fred"; lastName = "Flintstone" } : { firstName : Text; lastName : Text }
+```

src/mo_frontend/typing.ml

@@ -1236,6 +1236,12 @@ and check_exp' env0 t exp : T.typ =
     check_ids env "object" "field"
       (List.map (fun (ef : exp_field) -> ef.it.id) exp_fields);
     List.iter (fun ef -> check_exp_field env ef fts) exp_fields;
+    List.iter (fun ft ->
+      if not (List.exists (fun (ef : exp_field) -> ft.T.lab = ef.it.id.it) exp_fields)
+      then local_error env exp.at "M0151"
+        "object literal is missing field %s from expected type\n  %s"
+        ft.T.lab (T.string_of_typ_expand t);
+    ) fts;
     t
   | OptE exp1, _ when T.is_opt t ->
     check_exp env (T.as_opt t) exp1;

test/fail/check-record.mo

@@ -13,6 +13,8 @@ ignore ({ a = 0; var v = 0} : { var a : Int;  v : Int }); // reject, mutability
 
 ignore ({} : { a: Nat }); // reject
 
+ignore ({ a = 0; b = 1} : { a: Nat }); // accept (but warn in the future?)
+
 do {
   let a = 1;
   let b = 2;

test/fail/issue2331.mo

@@ -0,0 +1 @@
+ignore ({foo = 0} : { bar : Nat });

test/fail/ok/check-record.tc.ok

@@ -7,4 +7,6 @@ but found mutable 'var' field (delete 'var'?)
 check-record.mo:12.11-12.16: type error [M0149], expected mutable 'var' field a of type
   Int
 but found immutable field (insert 'var'?)
-check-record.mo:19.30-19.31: type error [M0057], unbound variable c
+check-record.mo:14.9-14.11: type error [M0151], object literal is missing field a from expected type
+  {a : Nat}
+check-record.mo:21.30-21.31: type error [M0057], unbound variable c

test/fail/ok/issue2331.tc.ok

@@ -0,0 +1,2 @@
+issue2331.mo:1.9-1.18: type error [M0151], object literal is missing field bar from expected type
+  {bar : Nat}

test/fail/ok/issue2331.tc.ret.ok

@@ -0,0 +1 @@
+Return code 1

test/run-drun/await-without-yield.mo

@@ -16,7 +16,7 @@ actor a {
     ignore(0/0);
   };
 
-  public func go() {
+  public func go() : async () {
     try {
       await bar();
       Prim.debugPrint("Huh, bar() replied?");

test/run-drun/ok/await-without-yield.drun-run.ok

@@ -1,3 +1,4 @@
 ingress Completed: Reply: 0x4449444c016c01b3c4b1f204680100010a00000000000000000101
 ingress Completed: Reply: 0x4449444c0000
+debug.print: 2
 ingress Completed: Reply: 0x4449444c0000