add Warn if no fields are given in a record update

src/typ/error.rs

@@ -218,6 +218,8 @@ pub enum Warning {
     Todo { location: SrcSpan },
 
     ImplicitlyDiscardedResult { location: SrcSpan },
+
+    NoFieldsRecordUpdate { location: SrcSpan },
 }
 
 #[derive(Debug, PartialEq)]

src/typ/expr.rs

@@ -1289,6 +1289,14 @@ impl<'a, 'b> ExprTyper<'a, 'b> {
                     )
                     .collect::<Result<_, _>>()?;
 
+                if args.is_empty() {
+                    self.environment
+                        .warnings
+                        .push(Warning::NoFieldsRecordUpdate {
+                            location: location.clone(),
+                        });
+                }
+
                 return Ok(TypedExpr::RecordUpdate {
                     location,
                     typ: spread.typ(),

src/typ/tests.rs

@@ -2952,6 +2952,35 @@ fn main() { foo(); 5 }",
 fn foo() { Ok(5) }
 fn main() { let _ = foo(); 5 }",
     );
+
+    // Some fields are given in a record update do not emit warnings
+    assert_no_warnings!(
+        "
+        pub type Person {
+            Person(name: String, age: Int)
+        };
+        pub fn update_person() {
+            let past = Person(\"Quinn\", 27)
+            let present = Person(..past, name: \"Santi\")
+            present
+        }",
+    );
+
+    // No fields are given in a record update emit warnings
+    assert_warning!(
+        "
+        pub type Person {
+            Person(name: String, age: Int)
+        };
+        pub fn update_person() {
+            let past = Person(\"Quinn\", 27)
+            let present = Person(..past)
+            present
+        }",
+        Warning::NoFieldsRecordUpdate {
+            location: SrcSpan { start: 183, end: 197 }
+        }
+    );
 }
 
 fn env_types_with(things: &[&str]) -> Vec<String> {

src/warning.rs

@@ -49,6 +49,17 @@ impl Warning {
                     write(buffer, diagnostic, Severity::Warning);
                     writeln!(buffer, "The Result value returned by this code is not being used, so any error is being silently ignored. Check for an error with a case statement, or assign it to the variable _ if you are sure the error does not matter.").unwrap();
                 }
+                NoFieldsRecordUpdate { location } => {
+                    let diagnostic = Diagnostic {
+                        title: "No fields are given in a record update".to_string(),
+                        label: "".to_string(),
+                        file: path.to_str().unwrap().to_string(),
+                        src: src.to_string(),
+                        location: location.clone(),
+                    };
+                    write(buffer, diagnostic, Severity::Warning);
+                    writeln!(buffer, "The Record Update in this code is no fields are given.").unwrap();
+                }
             },
         }
     }