PPX v4: mark props type in externals as @live. (#6796)

* PPX v4: mark props type in externals as `@live`.

Fixes rescript-lang/rescript-vscode#994

Dead code elimination in the editor tooling complains about props never being read in the `props` type record defined by the V4 ppx.
This is because externals don't provide the implementation of the component, and it's in the implementation that props could be read.
This OR marks the `props` type definition as `@live` for external components, so the dead code analysis does not fire.

* Update CHANGELOG.md

Author: cristianoc

CHANGELOG.md

@@ -15,6 +15,7 @@
 #### :bug: Bug Fix
 
 - Fix location of let bindings with attributes. https://github.com/rescript-lang/rescript-compiler/pull/6791
+- PPX v4: mark props type in externals as `@live` to avoid dead code warnings for prop fields in the editor tooling. https://github.com/rescript-lang/rescript-compiler/pull/6796
 
 # 11.1.1
 

jscomp/syntax/src/jsx_v4.ml

@@ -323,15 +323,15 @@ let makeLabelDecls namedTypeList =
            Type.field ~loc ~attrs {txt = label; loc}
              (Typ.var @@ safeTypeFromValue @@ Labelled label))
 
-let makeTypeDecls propsName loc namedTypeList =
+let makeTypeDecls ~attrs propsName loc namedTypeList =
   let labelDeclList = makeLabelDecls namedTypeList in
   (* 'id, 'className, ... *)
   let params =
     makePropsTypeParamsTvar namedTypeList
     |> List.map (fun coreType -> (coreType, Invariant))
   in
   [
-    Type.mk ~loc ~params {txt = propsName; loc}
+    Type.mk ~attrs ~loc ~params {txt = propsName; loc}
       ~kind:(Ptype_record labelDeclList);
   ]
 
@@ -342,21 +342,25 @@ let makeTypeDeclsWithCoreType propsName loc coreType typVars =
       ~manifest:coreType;
   ]
 
+let live_attr = ({txt = "live"; loc = Location.none}, PStr [])
+
 (* type props<'x, 'y, ...> = { x: 'x, y?: 'y, ... } *)
-let makePropsRecordType ~coreTypeOfAttr ~typVarsOfCoreType propsName loc
-    namedTypeList =
+let makePropsRecordType ~coreTypeOfAttr ~external_ ~typVarsOfCoreType propsName
+    loc namedTypeList =
+  let attrs = if external_ then [live_attr] else [] in
   Str.type_ Nonrecursive
     (match coreTypeOfAttr with
-    | None -> makeTypeDecls propsName loc namedTypeList
+    | None -> makeTypeDecls ~attrs propsName loc namedTypeList
     | Some coreType ->
       makeTypeDeclsWithCoreType propsName loc coreType typVarsOfCoreType)
 
 (* type props<'x, 'y, ...> = { x: 'x, y?: 'y, ... } *)
-let makePropsRecordTypeSig ~coreTypeOfAttr ~typVarsOfCoreType propsName loc
-    namedTypeList =
+let makePropsRecordTypeSig ~coreTypeOfAttr ~external_ ~typVarsOfCoreType
+    propsName loc namedTypeList =
+  let attrs = if external_ then [live_attr] else [] in
   Sig.type_ Nonrecursive
     (match coreTypeOfAttr with
-    | None -> makeTypeDecls propsName loc namedTypeList
+    | None -> makeTypeDecls ~attrs propsName loc namedTypeList
     | Some coreType ->
       makeTypeDeclsWithCoreType propsName loc coreType typVarsOfCoreType)
 
@@ -934,8 +938,8 @@ let mapBinding ~config ~emptyLoc ~pstr_loc ~fileName ~recFlag binding =
     let namedTypeList = List.fold_left argToType [] namedArgList in
     (* type props = { ... } *)
     let propsRecordType =
-      makePropsRecordType ~coreTypeOfAttr ~typVarsOfCoreType "props" pstr_loc
-        namedTypeList
+      makePropsRecordType ~coreTypeOfAttr ~external_:false ~typVarsOfCoreType
+        "props" pstr_loc namedTypeList
     in
     let innerExpression =
       Exp.apply
@@ -1188,8 +1192,8 @@ let transformStructureItem ~config item =
       in
       (* type props<'x, 'y> = { x: 'x, y?: 'y, ... } *)
       let propsRecordType =
-        makePropsRecordType ~coreTypeOfAttr ~typVarsOfCoreType "props" pstr_loc
-          namedTypeList
+        makePropsRecordType ~coreTypeOfAttr ~external_:true ~typVarsOfCoreType
+          "props" pstr_loc namedTypeList
       in
       (* can't be an arrow because it will defensively uncurry *)
       let newExternalType =
@@ -1294,9 +1298,10 @@ let transformSignatureItem ~config item =
             | [] -> []
             | _ -> [Typ.any ()]))
       in
+      let external_ = psig_desc.pval_prim <> [] in
       let propsRecordType =
-        makePropsRecordTypeSig ~coreTypeOfAttr ~typVarsOfCoreType "props"
-          psig_loc namedTypeList
+        makePropsRecordTypeSig ~coreTypeOfAttr ~external_ ~typVarsOfCoreType
+          "props" psig_loc namedTypeList
       in
       (* can't be an arrow because it will defensively uncurry *)
       let newExternalType =

jscomp/syntax/tests/ppx/react/expected/externalWithCustomName.res.txt

@@ -13,6 +13,7 @@ let t = React.createElement(Foo.component, Foo.componentProps(~a=1, ~b={"1"}, ()
 @@jsxConfig({version: 4, mode: "classic"})
 
 module Foo = {
+  @live
   type props<'a, 'b> = {a: 'a, b: 'b}
 
   @module("Foo")
@@ -24,6 +25,7 @@ let t = React.createElement(Foo.component, {a: 1, b: "1"})
 @@jsxConfig({version: 4, mode: "automatic"})
 
 module Foo = {
+  @live
   type props<'a, 'b> = {a: 'a, b: 'b}
 
   @module("Foo")

jscomp/syntax/tests/ppx/react/expected/externalWithRef.res.txt

@@ -18,6 +18,7 @@ module V3 = {
 @@jsxConfig({version: 4, mode: "classic"})
 
 module V4C = {
+  @live
   type props<'x, 'ref> = {
     x: 'x,
     ref?: 'ref,
@@ -28,9 +29,21 @@ module V4C = {
     "component"
 }
 
+module type V4CType = {
+  @live
+  type props<'x, 'y> = {
+    x: 'x,
+    y: 'y,
+  }
+
+  @module("someModule")
+  external make: React.componentLike<props<string, string>, React.element> = "component"
+}
+
 @@jsxConfig({version: 4, mode: "automatic"})
 
 module V4C = {
+  @live
   type props<'x, 'ref> = {
     x: 'x,
     ref?: 'ref,

jscomp/syntax/tests/ppx/react/expected/externalWithTypeVariables.res.txt

@@ -16,6 +16,7 @@ module V3 = {
 @@jsxConfig({version: 4, mode: "classic"})
 
 module V4C = {
+  @live
   type props<'x, 'children> = {
     x: 'x,
     children: 'children,
@@ -28,6 +29,7 @@ module V4C = {
 @@jsxConfig({version: 4, mode: "automatic"})
 
 module V4C = {
+  @live
   type props<'x, 'children> = {
     x: 'x,
     children: 'children,

jscomp/syntax/tests/ppx/react/expected/firstClassModules.res.txt

@@ -88,6 +88,7 @@ module External = {
     type key
     type t
   }
+  @live
   type props<'model, 'selected, 'onChange, 'items> = {
     model: 'model,
     selected: 'selected,

jscomp/syntax/tests/ppx/react/expected/mangleKeyword.res.txt

@@ -47,6 +47,7 @@ module C4C0 = {
   }
 }
 module C4C1 = {
+  @live
   type props<'T_open, 'T_type> = {@as("open") _open: 'T_open, @as("type") _type: 'T_type}
 
   external make: @as("open") React.componentLike<props<string, string>, React.element> = "default"
@@ -68,6 +69,7 @@ module C4A0 = {
   }
 }
 module C4A1 = {
+  @live
   type props<'T_open, 'T_type> = {@as("open") _open: 'T_open, @as("type") _type: 'T_type}
 
   external make: @as("open") React.componentLike<props<string, string>, React.element> = "default"

jscomp/syntax/tests/ppx/react/expected/noPropsWithKey.res.txt

@@ -12,6 +12,7 @@ module V4CA = {
 }
 
 module V4CB = {
+  @live
   type props = {}
 
   @module("c")
@@ -51,6 +52,7 @@ module V4CA = {
 }
 
 module V4CB = {
+  @live
   type props = {}
 
   @module("c")

jscomp/syntax/tests/ppx/react/expected/v4.res.txt

@@ -35,12 +35,14 @@ module type TUncurried = {
 }
 
 module E = {
+  @live
   type props<'x> = {x: 'x}
 
   external make: React.componentLike<props<string>, React.element> = "default"
 }
 
 module EUncurried = {
+  @live
   type props<'x> = {x: 'x}
 
   external make: React.componentLike<props<string>, React.element> = "default"

jscomp/syntax/tests/ppx/react/externalWithRef.res

@@ -18,6 +18,14 @@ module V4C = {
     ) => React.element = "component"
 }
 
+module type V4CType = {
+  @module("someModule") @react.component
+    external make: (
+      ~x: string,
+      ~y: string,
+    ) => React.element = "component"
+}
+
 @@jsxConfig({version: 4, mode: "automatic"})
 
 module V4C = {