Optimise comparison with singleton custom types on JavaScript #4903. …

compiler-core/src/analyse.rs

@@ -51,9 +51,10 @@ use vec1::Vec1;
 
 use self::imports::Importer;
 
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub enum Inferred<T> {
     Known(T),
+    #[default]
     Unknown,
 }
 

compiler-core/src/ast.rs

@@ -2473,12 +2473,6 @@ impl<T> BitArraySize<T> {
     }
 }
 
-impl Default for Inferred<()> {
-    fn default() -> Self {
-        Self::Unknown
-    }
-}
-
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum AssignName {
     Variable(EcoString),

compiler-core/src/erlang.rs

@@ -708,7 +708,7 @@ fn string_inner(value: &str) -> Document<'_> {
         .replace_all(value, |caps: &Captures<'_>| {
             let slashes = caps.get(1).map_or("", |m| m.as_str());
 
-            if slashes.len() % 2 == 0 {
+            if slashes.len().is_multiple_of(2) {
                 format!("{slashes}u")
             } else {
                 format!("{slashes}x")

compiler-core/src/javascript/expression.rs

@@ -1536,14 +1536,76 @@ impl<'module, 'a> Generator<'module, 'a> {
             return docvec![left_doc, operator, right_doc];
         }
 
+        // For comparison with singleton custom types, ie, one with no fields.
+        // If you have some code like this
+        // ```gleam
+        //  pub type Wibble {
+        //    Wibble
+        //    Wobble
+        //  }
+
+        //  pub fn is_wibble(w: Wibble) -> Bool {
+        //    w == Wibble
+        //  }
+        // ```
+        // Instead of `isEqual(w, new Wibble())`, generate `w instanceof Wibble`
+        // because the first approach needs to construct a new Wibble, and then call the isEqual function,
+        // which supports any shape of data, and so does a lot of extra logic which isn't necessary.
+
+        // RHS: singleton record constructor (arity 0)
+        if let TypedExpr::Var {
+            constructor:
+                ValueConstructor {
+                    variant: ValueConstructorVariant::Record { arity: 0, name, .. },
+                    ..
+                },
+            ..
+        } = right
+        {
+            let left = self
+                .not_in_tail_position(Some(Ordering::Strict), |this| this.wrap_expression(left));
+
+            return self.singleton_equal(left, name, should_be_equal);
+        }
+
+        // LHS: singleton record constructor (arity 0)
+        if let TypedExpr::Var {
+            constructor:
+                ValueConstructor {
+                    variant: ValueConstructorVariant::Record { arity: 0, name, .. },
+                    ..
+                },
+            ..
+        } = left
+        {
+            let right = self
+                .not_in_tail_position(Some(Ordering::Strict), |this| this.wrap_expression(right));
+
+            return self.singleton_equal(right, name, should_be_equal);
+        }
+
         // Other types must be compared using structural equality
         let left =
             self.not_in_tail_position(Some(Ordering::Strict), |this| this.wrap_expression(left));
         let right =
             self.not_in_tail_position(Some(Ordering::Strict), |this| this.wrap_expression(right));
+
         self.prelude_equal_call(should_be_equal, left, right)
     }
 
+    fn singleton_equal(
+        &self,
+        value: Document<'a>,
+        tag: &EcoString,
+        should_be_equal: bool,
+    ) -> Document<'a> {
+        if should_be_equal {
+            docvec![value, " instanceof ", tag.to_doc()]
+        } else {
+            docvec!["!(", value, " instanceof ", tag.to_doc(), ")"]
+        }
+    }
+
     fn equal_with_doc_operands(
         &mut self,
         left: Document<'a>,
@@ -1966,16 +2028,42 @@ impl<'module, 'a> Generator<'module, 'a> {
                 docvec![left, " !== ", right]
             }
 
-            ClauseGuard::Equals { left, right, .. } => {
-                let left = self.guard(left);
-                let right = self.guard(right);
-                self.prelude_equal_call(true, left, right)
-            }
+            ClauseGuard::Equals { left, right, .. }
+            | ClauseGuard::NotEquals { left, right, .. } => {
+                fn eligible_singleton_cmp(
+                    lhs: &TypedClauseGuard,
+                    rhs: &TypedClauseGuard,
+                ) -> Option<EcoString> {
+                    match rhs {
+                        ClauseGuard::Constant(Constant::Record {
+                            arguments, name, ..
+                        }) if arguments.is_empty() && rhs.type_().is_named() => {
+                            // exclude the `Type::Fn` case
+                            if !matches!(lhs,
+                                ClauseGuard::Var { type_, .. } if matches!(&**type_, Type::Fn { .. }))
+                            {
+                                return Some(name.clone());
+                            }
+                        }
+                        _ => {}
+                    }
+                    None
+                }
+
+                let should_be_equal = matches!(guard, ClauseGuard::Equals { .. });
+
+                if let Some(tag) = eligible_singleton_cmp(left, right) {
+                    let doc = self.guard(left);
+                    return self.singleton_equal(doc, &tag, should_be_equal);
+                }
+                if let Some(tag) = eligible_singleton_cmp(right, left) {
+                    let doc = self.guard(right);
+                    return self.singleton_equal(doc, &tag, should_be_equal);
+                }
 
-            ClauseGuard::NotEquals { left, right, .. } => {
                 let left = self.guard(left);
                 let right = self.guard(right);
-                self.prelude_equal_call(false, left, right)
+                self.prelude_equal_call(should_be_equal, left, right)
             }
 
             ClauseGuard::GtFloat { left, right, .. } | ClauseGuard::GtInt { left, right, .. } => {

compiler-core/src/javascript/tests/custom_types.rs

@@ -687,3 +687,218 @@ pub type Wibble {
 "#
     );
 }
+
+#[test]
+fn singleton_record_equality() {
+    assert_js!(
+        r#"
+pub type Wibble {
+  Wibble
+  Wobble
+}
+
+pub fn is_wibble(w: Wibble) -> Bool {
+  w == Wibble
+}
+"#,
+    );
+}
+
+#[test]
+fn singleton_record_inequality() {
+    assert_js!(
+        r#"
+pub type Wibble {
+  Wibble
+  Wobble
+}
+
+pub fn is_not_wibble(w: Wibble) -> Bool {
+  w != Wibble
+}
+"#,
+    );
+}
+
+#[test]
+fn singleton_record_reverse_order() {
+    assert_js!(
+        r#"
+pub type Wibble {
+  Wibble
+  Wobble
+}
+
+pub fn is_wibble_reverse(w: Wibble) -> Bool {
+  Wibble == w
+}
+"#,
+    );
+}
+
+#[test]
+fn non_singleton_record_equality() {
+    assert_js!(
+        r#"
+pub type Person {
+  Person(name: String, age: Int)
+}
+
+pub fn same_person(p1: Person, p2: Person) -> Bool {
+  p1 == p2
+}
+"#,
+    );
+}
+
+#[test]
+fn multiple_singleton_constructors() {
+    assert_js!(
+        r#"
+pub type Status {
+  Loading
+  Success
+  Error
+}
+
+pub fn is_loading(s: Status) -> Bool {
+  s == Loading
+}
+
+pub fn is_success(s: Status) -> Bool {
+  s == Success
+}
+"#,
+    );
+}
+
+#[test]
+fn mixed_singleton_and_non_singleton() {
+    assert_js!(
+        r#"
+pub type Result {
+  Ok(value: Int)
+  Error
+}
+
+pub fn is_error(r: Result) -> Bool {
+  r == Error
+}
+"#,
+    );
+}
+
+#[test]
+fn singleton_in_case_guard() {
+    assert_js!(
+        r#"
+pub type State {
+  Active
+  Inactive
+}
+
+pub fn process(s: State) -> String {
+  case s {
+    state if state == Active -> "active"
+    _ -> "inactive"
+  }
+}
+"#,
+    );
+}
+
+#[test]
+fn variant_defined_in_another_module_qualified_expression() {
+    assert_js!(
+        (
+            "other_module",
+            r#"pub type Thingy { Variant OtherVariant }"#
+        ),
+        r#"
+import other_module
+
+pub fn check(x) -> Bool {
+  x == other_module.Variant
+}
+"#,
+    );
+}
+
+#[test]
+fn variant_defined_in_another_module_unqualified_expression() {
+    assert_js!(
+        ("other_module", r#"pub type Thingy { Variant Other(Int) }"#),
+        r#"
+import other_module.{Variant}
+
+pub fn check(x) -> Bool {
+  x == Variant
+}
+"#,
+    );
+}
+
+#[test]
+fn variant_defined_in_another_module_aliased_expression() {
+    assert_js!(
+        ("other_module", r#"pub type Thingy { Variant Other(Int) }"#),
+        r#"
+import other_module.{Variant as Aliased}
+
+pub fn check(x) -> Bool {
+  x == Aliased
+}
+"#,
+    );
+}
+
+#[test]
+fn variant_defined_in_another_module_qualified_clause_guard() {
+    assert_js!(
+        ("other_module", r#"pub type Thingy { Variant Other(Int) }"#),
+        r#"
+import other_module
+
+pub fn process(e) -> String {
+  case e {
+    value if value == other_module.Variant -> "match"
+    _ -> "no match"
+  }
+}
+"#,
+    );
+}
+
+#[test]
+fn variant_defined_in_another_module_unqualified_clause_guard() {
+    assert_js!(
+        ("other_module", r#"pub type Thingy { Variant Other(Int) }"#),
+        r#"
+import other_module.{Variant}
+
+pub fn process(e) -> String {
+  case e {
+    value if value == Variant -> "match"
+    _ -> "no match"
+  }
+}
+"#,
+    );
+}
+
+#[test]
+fn variant_defined_in_another_module_aliased_clause_guard() {
+    assert_js!(
+        ("other_module", r#"pub type Thingy { Variant Other(Int) }"#),
+        r#"
+import other_module.{Variant as Aliased}
+
+pub fn process(e) -> String {
+  case e {
+    value if value == Aliased -> "match"
+    _ -> "no match"
+  }
+}
+"#,
+    );
+}