Add regression tests for external components in JSX preserve mode

tests/ERROR_VARIANTS.md

@@ -207,7 +207,7 @@ Source: [typecore.ml:27](../compiler/ml/typecore.ml).
 | `Or_pattern_type_clash` | ✓ | `or_pattern_type_clash.res` | |
 | `Multiply_bound_variable` | ✓ | `multiply_bound_variable.res` | |
 | `Orpat_vars` | ✓ | `orpat_vars_unbalanced.res` | |
-| `Expr_type_clash` | ✓ | many `*.res` | Most-fired expression error. Trace-shape sub-cases covered: `if_return_type_mismatch.res` (IfReturn), `maybe_unwrap_option.res` (MaybeUnwrapOption), `string_concat_non_string.res` (StringConcat), `labeled_fn_argument_type_clash.res` (FunctionArgument with explicit label), `math_operator_*.res` (MathOperator family), `ternary_branch_mismatch.res`, `switch_different_types.res`, `try_catch_same_type.res`, `comparison_operator.res`, `array_item_type_mismatch.res`, `array_literal_passed_to_tuple.res`, `if_condition_mismatch.res`, `while_condition.res`, `for_loop_condition.res`, `assert_condition.res`, `function_call_mismatch.res`, `awaiting_non_promise.res`, multiple `jsx_*` fixtures, `object_literal_for_poly_field.res` (object literal against a polymorphic field annotation). |
+| `Expr_type_clash` | ✓ | many `*.res` | Most-fired expression error. Trace-shape sub-cases covered: `if_return_type_mismatch.res` (IfReturn), `maybe_unwrap_option.res` (MaybeUnwrapOption), `string_concat_non_string.res` (StringConcat), `labeled_fn_argument_type_clash.res` (FunctionArgument with explicit label), `math_operator_*.res` (MathOperator family), `ternary_branch_mismatch.res`, `switch_different_types.res`, `try_catch_same_type.res`, `comparison_operator.res`, `array_item_type_mismatch.res`, `array_literal_passed_to_tuple.res`, `if_condition_mismatch.res`, `while_condition.res`, `for_loop_condition.res`, `assert_condition.res`, `function_call_mismatch.res`, `awaiting_non_promise.res`, multiple `jsx_*` fixtures (including `jsx_preserve_external_function.res` for a plain-function external in a JSX component position), `object_literal_for_poly_field.res` (object literal against a polymorphic field annotation). |
 | `Apply_non_function` | ✓ | `apply_non_function.res` | |
 | `Apply_wrong_label` | ✓ | `apply_wrong_label.res` | |
 | `Label_multiply_defined` | ✓ | `label_multiply_defined_literal.res` | |

tests/build_tests/jsx_preserve_external/input.js

@@ -0,0 +1,15 @@
+// @ts-check
+
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { setup } from "#dev/process";
+
+const { execBuildOrThrow, execClean } = setup(import.meta.dirname);
+
+await execClean();
+await execBuildOrThrow();
+
+const output = readFileSync(new URL("src/Test.jsx", import.meta.url), "utf8");
+assert.match(output, /import \* as SomeLib from "some-lib"/);
+assert.match(output, /<SomeLib\.Head>\s*\{<div\s*\/>\}\s*<\/SomeLib\.Head>/);
+assert.doesNotMatch(output, /=>/);

tests/build_tests/jsx_preserve_external/rescript.json

@@ -0,0 +1,14 @@
+{
+  "name": "jsx-preserve-external",
+  "sources": ["src"],
+  "package-specs": {
+    "module": "esmodule",
+    "in-source": true,
+    "suffix": ".jsx"
+  },
+  "jsx": {
+    "module": "Preact",
+    "preserve": true
+  },
+  "compiler-flags": ["-check-lam"]
+}

tests/build_tests/jsx_preserve_external/src/Preact.res

@@ -0,0 +1,23 @@
+type element = Jsx.element
+// Custom JSX bindings must use the abstract component type, as React does.
+// A function alias here lets function-style externals through and can produce
+// invalid preserved JSX, as in the original bindings from issue #8047.
+type component<'props> = Jsx.component<'props>
+
+@module("preact/jsx-runtime")
+external jsx: (component<'props>, 'props) => element = "jsx"
+
+@module("preact/jsx-runtime")
+external jsxs: (component<'props>, 'props) => element = "jsxs"
+
+type domProps = {children?: element}
+
+module Elements = {
+  external someElement: element => option<element> = "%identity"
+
+  @module("preact/jsx-runtime")
+  external jsx: (string, domProps) => element = "jsx"
+
+  @module("preact/jsx-runtime")
+  external jsxs: (string, domProps) => element = "jsxs"
+}

tests/build_tests/jsx_preserve_external/src/Test.res

@@ -0,0 +1,13 @@
+// Regression for https://github.com/rescript-lang/rescript/issues/8047.
+// External components must remain imported values, without function wrappers.
+module Head = {
+  type props = {children?: Preact.element}
+
+  @module("some-lib")
+  external make: Preact.component<props> = "Head"
+}
+
+let test =
+  <Head>
+    <div />
+  </Head>

tests/build_tests/super_errors/expected/jsx_preserve_external_function.res.expected

@@ -0,0 +1,20 @@
+
+  We've found a bug for you!
+  /.../fixtures/jsx_preserve_external_function.res:30:4-7
+
+  28 │ 
+  29 │ let test =
+  30 │   <Head>
+  31 │     <div />
+  32 │   </Head>
+
+  This JSX tag has type: Head.props => Preact.element
+  But JSX component positions require:
+    Preact.component<'a> (defined as Jsx.component<'a>)
+
+  JSX tags must be React components, not plain functions.
+
+  Possible solutions:
+  - If this function takes labeled props, annotate it with @react.component
+  - If this function takes a single props record, annotate it with @react.componentWithProps
+  - If this is already a valid component-like value, wrap it with React.component(...)

tests/build_tests/super_errors/fixtures/jsx_preserve_external_function.res

@@ -0,0 +1,32 @@
+@@config({flags: ["-bs-jsx-preserve"]})
+@@jsxConfig({version: 4, module_: "Preact"})
+
+// With abstract components, the function-style external from #8047 is rejected.
+module Preact = {
+  type element = Jsx.element
+  type component<'props> = Jsx.component<'props>
+
+  @module("preact/jsx-runtime")
+  external jsx: (component<'props>, 'props) => element = "jsx"
+
+  type domProps = {children?: element}
+
+  module Elements = {
+    external someElement: element => option<element> = "%identity"
+
+    @module("preact/jsx-runtime")
+    external jsx: (string, domProps) => element = "jsx"
+  }
+}
+
+module Head = {
+  type props = {children?: Preact.element}
+
+  @module("some-lib")
+  external make: props => Preact.element = "Head"
+}
+
+let test =
+  <Head>
+    <div />
+  </Head>