feat(compiler): Introduce warning if non-void expression value not used or ignored

Author: alex-snezhko

compiler/src/typed/typecore.re

@@ -2231,11 +2231,10 @@ and type_statement_expr = (~explanation=?, ~in_function=?, env, sexp) => {
     /*| Tarrow _ -> [not really applicable with our syntax]
       Location.prerr_warning loc Warnings.Partial_application*/
     | TTyConstr(p, _, _) when Path.same(p, Builtin_types.path_void) => ()
+    | TTyVar(None) => ()
     /*| Tvar _ ->
       add_delayed_check (fun () -> check_application_result env true exp)*/
-    | _ => ()
-    /* This isn't quite relevant to Grain mechanics
-       Location.prerr_warning loc Grain_utils.Warnings.StatementType */
+    | _ => Location.prerr_warning(loc, Grain_utils.Warnings.StatementType)
     };
     unify_var(env, tv, ty);
     exp;

compiler/src/utils/warnings.re

@@ -101,7 +101,7 @@ let message =
     "these field labels belong to several types: "
     ++ String.concat(" ", tl)
     ++ "\nThe first one was selected. Please disambiguate if this is wrong."
-  | StatementType => "this expression should have type void."
+  | StatementType => "this expression should have type void. Use `ignore` to ignore the result of the expression"
   | NonreturningStatement => "this statement never returns (or has an unsound type)."
   | AllClausesGuarded => "this pattern-matching is not exhaustive.\nAll clauses in this pattern-matching are guarded."
   | PartialMatch("") => "this pattern-matching is not exhaustive."

compiler/test/input/wasiPolyfill.gr

@@ -14,8 +14,8 @@ provide let fd_write: (WasmI32, WasmI32, WasmI32, WasmI32) => WasmI32 =
     iovs_len,
     nwritten,
   ) => {
-  fd_write(fd, iovs, iovs_len, nwritten)
-  fd_write(fd, iovs, iovs_len, nwritten)
+  let _ = fd_write(fd, iovs, iovs_len, nwritten)
+  let _ = fd_write(fd, iovs, iovs_len, nwritten)
   fd_write(fd, iovs, iovs_len, nwritten)
 }
 

compiler/test/runner.re

@@ -206,6 +206,7 @@ let makeSnapshotRunner =
     (~config_fn=?, test, ~module_header=module_header, name, prog) => {
   test(name, ({expect}) => {
     Config.preserve_all_configs(() => {
+      Config.print_warnings := false;
       ignore @@
       compile(
         ~hook=stop_after_object_file_emitted,
@@ -234,6 +235,7 @@ let makeFilesizeRunner =
 let makeSnapshotFileRunner = (test, ~config_fn=?, name, filename) => {
   test(name, ({expect}) => {
     Config.preserve_all_configs(() => {
+      Config.print_warnings := false;
       let infile = grainfile(filename);
       let outfile = wasmfile(name);
       ignore @@

compiler/test/stdlib/array.test.gr

@@ -835,7 +835,7 @@ module Immutable {
 
   // Array.rotate
   let arr1 = fromList([1, 2, 3, 4, 5])
-  Array.rotate(0, arr1)
+  ignore(Array.rotate(0, arr1))
   assert arr1 == fromList([1, 2, 3, 4, 5])
 
   let arr2 = fromList([1, 2, 3, 4, 5])

compiler/test/stdlib/char.test.gr

@@ -51,7 +51,7 @@ while (!done) {
     break
   }
 
-  Char.code(chars[charPosition])
+  ignore(Char.code(chars[charPosition]))
   charPosition += 1
 }
 

compiler/test/stdlib/path.test.gr

@@ -216,8 +216,8 @@ List.forEach(({ base, toAppend, final }) => {
   assert append == Ok(expPath)
 }, appendTests)
 
-Path.append(fs("file"), fs("f")) == Err(Path.AppendToFile)
-Path.append(fs("/d/"), fs("/f")) == Err(Path.AppendAbsolute)
+assert Path.append(fs("file"), fs("f")) == Err(Path.AppendToFile)
+assert Path.append(fs("/d/"), fs("/f")) == Err(Path.AppendAbsolute)
 
 record RelativeToDirTestData {
   source: String,

compiler/test/stdlib/queue.test.gr

@@ -29,7 +29,7 @@ Queue.push(4, queue)
 assert Queue.size(queue) == 3
 assert Queue.peek(queue) == Some(2)
 let copy = Queue.copy(queue)
-Queue.pop(copy)
+ignore(Queue.pop(copy))
 assert Queue.size(copy) == 2
 assert Queue.size(queue) == 3
 Queue.clear(queue)
@@ -61,11 +61,11 @@ Queue.push(1, queue)
 Queue.push(2, queue)
 Queue.push(3, queue)
 assert Queue.toList(queue) == [0, 1, 2, 3]
-Queue.pop(queue)
+ignore(Queue.pop(queue))
 assert Queue.toList(queue) == [1, 2, 3]
 Queue.push(3, queue)
 assert Queue.toList(queue) == [1, 2, 3, 3]
-Queue.pop(queue)
+ignore(Queue.pop(queue))
 Queue.push(4, queue)
 Queue.push(5, queue)
 assert Queue.toList(queue) == [2, 3, 3, 4, 5]
@@ -121,12 +121,12 @@ Queue.push(1, queue2)
 Queue.push(2, queue2)
 Queue.push(3, queue2)
 Queue.push(4, queue2)
-Queue.pop(queue2)
-Queue.pop(queue2)
+ignore(Queue.pop(queue2))
+ignore(Queue.pop(queue2))
 Queue.push(5, queue2)
-Queue.pop(queue2)
-Queue.pop(queue2)
-Queue.pop(queue2)
+ignore(Queue.pop(queue2))
+ignore(Queue.pop(queue2))
+ignore(Queue.pop(queue2))
 Queue.push(6, queue2)
 Queue.push(7, queue2)
 Queue.push(8, queue2)
@@ -149,7 +149,7 @@ Queue.push(2, queue3)
 Queue.push(3, queue3)
 assert Queue.toArray(queue3) == [> 1, 2, 3]
 let queue4 = Queue.copy(queue3)
-Queue.pop(queue4)
+ignore(Queue.pop(queue4))
 assert Queue.toArray(queue4) == [> 2, 3]
 
 // Queue.fromArray
@@ -169,12 +169,12 @@ Queue.push(1, queue2)
 Queue.push(2, queue2)
 Queue.push(3, queue2)
 Queue.push(4, queue2)
-Queue.pop(queue2)
-Queue.pop(queue2)
+ignore(Queue.pop(queue2))
+ignore(Queue.pop(queue2))
 Queue.push(5, queue2)
-Queue.pop(queue2)
-Queue.pop(queue2)
-Queue.pop(queue2)
+ignore(Queue.pop(queue2))
+ignore(Queue.pop(queue2))
+ignore(Queue.pop(queue2))
 Queue.push(6, queue2)
 Queue.push(7, queue2)
 Queue.push(8, queue2)
@@ -194,7 +194,7 @@ Queue.push(1, queue3)
 Queue.push(2, queue3)
 Queue.push(3, queue3)
 let queue4 = Queue.copy(queue3)
-Queue.pop(queue4)
+ignore(Queue.pop(queue4))
 let queue5 = Queue.make()
 Queue.push(6, queue5)
 Queue.push(7, queue5)
@@ -222,7 +222,7 @@ Queue.push(3, queue7)
 assert queue4 == queue7
 let queue8 = Queue.make()
 Queue.push(1, queue8)
-Queue.pop(queue8)
+ignore(Queue.pop(queue8))
 assert queue8 == queue1
 
 assert !(queue2 == queue3)

compiler/test/stdlib/set.test.gr

@@ -327,7 +327,7 @@ module Immutable {
 
   let mut filterTestSet = makeTestSet()
 
-  Set.filter(key => fail "Shouldn't be called", Set.empty)
+  ignore(Set.filter(key => fail "Shouldn't be called", Set.empty))
   filterTestSet = Set.filter(key => key == Sheep, filterTestSet)
 
   assert !Set.contains(Grain, filterTestSet)
@@ -338,7 +338,7 @@ module Immutable {
 
   let mut rejectTestSet = makeTestSet()
 
-  Set.reject(key => fail "Shouldn't be called", Set.empty)
+  ignore(Set.reject(key => fail "Shouldn't be called", Set.empty))
   rejectTestSet = Set.reject(key => key == Sheep, rejectTestSet)
 
   assert Set.contains(Grain, rejectTestSet)

compiler/test/stdlib/stack.test.gr

@@ -28,7 +28,7 @@ Stack.push(4, stack)
 assert Stack.size(stack) == 3
 assert Stack.peek(stack) == Some(4)
 let copy = Stack.copy(stack)
-Stack.pop(copy)
+ignore(Stack.pop(copy))
 assert Stack.size(copy) == 2
 assert Stack.size(stack) == 3
 Stack.clear(stack)