anmonteiro · Oct 24, 2026
diff --git a/test/blackbox-tests/data-attributes.t/run.t b/test/blackbox-tests/data-attributes.t/run.t
@@ -0,0 +1,47 @@
+DOM JSX currently rejects arbitrary data attributes. These expected failures
+document the limitation before adding support for them.
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.8)
+  > (using melange 0.1)
+  > EOF
+
+  $ cat > dune <<EOF
+  > (melange.emit
+  >  (target output)
+  >  (alias mel)
+  >  (emit_stdlib false)
+  >  (libraries reason-react)
+  >  (preprocess (pps melange.ppx reason-react-ppx)))
+  > EOF
+
+Check the failure status before showing the final diagnostic, since the full
+list of accepted DOM props is long.
+
+  $ cat > input.re <<EOF
+  > let element = <div dataFoo="value" />;
+  > EOF
+  $ dune build @mel > error.log 2>&1
+  [1]
+  $ tail -n 1 error.log
+  This argument cannot be applied with label ~dataFoo
+
+Optional data attributes are also rejected.
+
+  $ cat > input.re <<EOF
+  > let element = (~dataFoo=?, ()) => <div ?dataFoo />;
+  > EOF
+  $ dune build @mel > error.log 2>&1
+  [1]
+  $ tail -n 1 error.log
+  This argument cannot be applied with label ?dataFoo
+
+SVG elements have the same limitation.
+
+  $ cat > input.re <<EOF
+  > let element = <svg dataFoo="value" />;
+  > EOF
+  $ dune build @mel > error.log 2>&1
+  [1]
+  $ tail -n 1 error.log
+  This argument cannot be applied with label ~dataFoo
diff --git a/test/blackbox-tests/dom-props.t/input.re.in b/test/blackbox-tests/dom-props.t/input.re.in
@@ -0,0 +1,45 @@
+let first = <div className="first" />;
+let second = <div id="second" />;
+let ordinaryData = <object data="file" datatype="text" />;
+
+let optional = (~className=?, ()) => <div ?className />;
+
+let renamed =
+  <div
+    ariaLabel="label"
+    ariaActivedescendant="descendant"
+    as_="button"
+    begin_="0"
+    end_="1"
+    in_="source"
+    open_=true
+    to_="target"
+    type_="button"
+  />;
+
+let withChildren = <div key="parent"> <span /> <span /> </div>;
+
+let withRefAndEvent = (elementRef, handleClick) =>
+  <button ref=elementRef onClick=handleClick />;
+
+let optionalKey = (~key=?, ()) => <div ?key />;
+
+module Component = {
+  [@react.component]
+  let make = (~dataFoo) => <div> dataFoo->React.string </div>;
+};
+
+let component = <Component dataFoo="component" />;
+
+module IntegerComponent = {
+  [@react.component]
+  let make = (~dataFoo: int) => <div> dataFoo->React.int </div>;
+};
+
+let integerComponent = <IntegerComponent dataFoo=42 />;
+
+external next: string => string = "next";
+let effects = <div className={next("class")} id={next("id")} />;
+
+external nextUnit: unit => unit = "nextUnit";
+let effectfulUnit = [@JSX] div(~className="unit", nextUnit());
diff --git a/test/blackbox-tests/dom-props.t/run.t b/test/blackbox-tests/dom-props.t/run.t
@@ -0,0 +1,227 @@
+DOM props retain their types and JavaScript names. Component props named
+dataFoo are ordinary component props, including when their type is int.
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.8)
+  > (using melange 0.1)
+  > EOF
+
+  $ cat > dune <<EOF
+  > (melange.emit
+  >  (target output)
+  >  (alias mel)
+  >  (emit_stdlib false)
+  >  (libraries reason-react)
+  >  (preprocess (pps melange.ppx reason-react-ppx)))
+  > EOF
+
+  $ cp input.re.in input.re
+  $ chmod u+w input.re
+  $ dune build @mel
+  $ cat _build/default/output/input.js
+  // Generated by Melange
+  'use strict';
+
+  const Caml_option = require("melange.js/caml_option.js");
+  const JsxRuntime = require("react/jsx-runtime");
+
+  const first = JsxRuntime.jsx("div", {
+    className: "first"
+  });
+
+  const second = JsxRuntime.jsx("div", {
+    id: "second"
+  });
+
+  const ordinaryData = JsxRuntime.jsx("object", {
+    data: "file",
+    datatype: "text"
+  });
+
+  function optional(className, param) {
+    let tmp = {};
+    if (className !== undefined) {
+      tmp.className = Caml_option.valFromOption(className);
+    }
+    return JsxRuntime.jsx("div", tmp);
+  }
+
+  const renamed = JsxRuntime.jsx("div", {
+    "aria-activedescendant": "descendant",
+    "aria-label": "label",
+    as: "button",
+    open: true,
+    type: "button",
+    begin: "0",
+    end: "1",
+    in: "source",
+    to: "target"
+  });
+
+  const withChildren = JsxRuntime.jsxs("div", {
+    children: [
+      JsxRuntime.jsx("span", {}),
+      JsxRuntime.jsx("span", {})
+    ]
+  }, "parent");
+
+  function withRefAndEvent(elementRef, handleClick) {
+    return JsxRuntime.jsx("button", {
+      ref: elementRef,
+      onClick: handleClick
+    });
+  }
+
+  function optionalKey(key, param) {
+    return JsxRuntime.jsx("div", {}, key !== undefined ? Caml_option.valFromOption(key) : undefined);
+  }
+
+  function Input$Component(Props) {
+    let dataFoo = Props.dataFoo;
+    return JsxRuntime.jsx("div", {
+      children: dataFoo
+    });
+  }
+
+  const Component = {
+    make: Input$Component
+  };
+
+  const component = JsxRuntime.jsx(Input$Component, {
+    dataFoo: "component"
+  });
+
+  function Input$IntegerComponent(Props) {
+    let dataFoo = Props.dataFoo;
+    return JsxRuntime.jsx("div", {
+      children: dataFoo
+    });
+  }
+
+  const IntegerComponent = {
+    make: Input$IntegerComponent
+  };
+
+  const integerComponent = JsxRuntime.jsx(Input$IntegerComponent, {
+    dataFoo: 42
+  });
+
+  const effects = JsxRuntime.jsx("div", {
+    className: next("class"),
+    id: next("id")
+  });
+
+  const effectfulUnit = JsxRuntime.jsx("div", (nextUnit(), {
+    className: "unit"
+  }));
+
+  module.exports = {
+    first,
+    second,
+    ordinaryData,
+    optional,
+    renamed,
+    withChildren,
+    withRefAndEvent,
+    optionalKey,
+    Component,
+    component,
+    IntegerComponent,
+    integerComponent,
+    effects,
+    effectfulUnit,
+  }
+  /* first Not a pure module */
+
+Ordinary prop types are checked.
+
+  $ cat > input.re <<EOF
+  > let element = <div className=42 />;
+  > EOF
+  $ dune build @mel
+  File "input.re", line 1, characters 29-31:
+  1 | let element = <div className=42 />;
+                                   ^^
+  Error: The constant 42 has type int but an expression was expected of type
+           string
+  [1]
+
+Optional ordinary prop types are checked too.
+
+  $ cat > input.re <<EOF
+  > let element = <div className=?Some(42) />;
+  > EOF
+  $ dune build @mel
+  File "input.re", line 1, characters 35-37:
+  1 | let element = <div className=?Some(42) />;
+                                         ^^
+  Error: The constant 42 has type int but an expression was expected of type
+           string
+  [1]
+
+Renamed props retain their original types.
+
+  $ cat > input.re <<EOF
+  > let element = <div open_="yes" />;
+  > EOF
+  $ dune build @mel
+  File "input.re", line 1, characters 25-30:
+  1 | let element = <div open_="yes" />;
+                               ^^^^^
+  Error: This constant has type string but an expression was expected of type
+           bool
+  [1]
+
+Unknown props fail. Show only the final diagnostic because the constructor's
+list of valid props is long, while checking the compiler's exit status separately.
+
+  $ cat > input.re <<EOF
+  > let element = <div clasName="typo" />;
+  > EOF
+  $ dune build @mel > error.log 2>&1
+  [1]
+  $ tail -n 1 error.log
+  This argument cannot be applied with label ~clasName
+
+Components must declare their dataFoo prop.
+
+  $ cat > input.re <<EOF
+  > module Component = {
+  >   [@react.component]
+  >   let make = () => React.null;
+  > };
+  > let element = <Component dataFoo="x" />;
+  > EOF
+  $ dune build @mel
+  File "input.re", line 5, characters 33-36:
+  5 | let element = <Component dataFoo="x" />;
+                                       ^^^
+  Error: The function applied to this argument has type
+           ?key:string -> <  > Js.t
+  This argument cannot be applied with label ~dataFoo
+  [1]
+
+Event handlers and refs retain their types.
+
+  $ cat > input.re <<EOF
+  > let element = <div onClick={event => event + 1} />;
+  > EOF
+  $ dune build @mel
+  File "input.re", line 1, characters 37-42:
+  1 | let element = <div onClick={event => event + 1} />;
+                                           ^^^^^
+  Error: The value event has type
+           React.Event.Mouse.t = React.Event.Mouse.tag React.Event.synthetic
+         but an expression was expected of type int
+  [1]
+
+  $ cat > input.re <<EOF
+  > let element = <div ref=42 />;
+  > EOF
+  $ dune build @mel
+  File "input.re", line 1, characters 23-25:
+  1 | let element = <div ref=42 />;
+                             ^^
+  Error: The constant 42 has type int but an expression was expected of type
+           ReactDOM.domRef
+  [1]