Add completion for throw keyword

CHANGELOG.md

@@ -33,6 +33,7 @@
 - Add (dev-)dependencies to build schema. https://github.com/rescript-lang/rescript/pull/7892
 - Dedicated error for dict literal spreads. https://github.com/rescript-lang/rescript/pull/7901
 - Dedicated error message for when mixing up `:` and `=` in various positions. https://github.com/rescript-lang/rescript/pull/7900
+- Add completions for `throw`. https://github.com/rescript-lang/rescript/pull/7905
 
 #### :house: Internal
 

analysis/src/CompletionBackEnd.ml

@@ -756,6 +756,38 @@ let getCompletionsForPath ~debug ~opens ~full ~pos ~exact ~scope
         findAllCompletions ~env ~prefix ~exact ~namesUsed ~completionContext
       | None -> []))
 
+let completionsForThrow ~(env : QueryEnv.t) ~full =
+  let exn_typ = Predef.type_exn in
+  let names_from_cmt =
+    let moduleName = env.file.moduleName in
+    match Hashtbl.find_opt full.package.pathsForModule moduleName with
+    | None -> []
+    | Some paths ->
+      let uri = getUri paths in
+      let cmt_path = getCmtPath ~uri paths in
+      ProcessCmt.exceptionsForCmt ~cmt:cmt_path
+  in
+  let completions_from_cmt =
+    names_from_cmt
+    |> List.map (fun (name, hasArgs) ->
+           let insertText =
+             if hasArgs then Printf.sprintf "throw(%s($0))" name
+             else Printf.sprintf "throw(%s)" name
+           in
+           Completion.create
+             (Printf.sprintf "throw(%s)" name)
+             ~env ~kind:(Completion.Value exn_typ) ~includesSnippets:true
+             ~insertText ~filterText:"throw")
+  in
+  Completion.create "JsError.throwWithMessage" ~env
+    ~kind:(Completion.Value exn_typ) ~includesSnippets:true
+    ~detail:"Throw a JavaScript error, example: `throw new Error(str)`"
+    ~insertText:"JsError.throwWithMessage(\"$0\")"
+  :: Completion.create "JsExn.throw" ~env ~kind:(Completion.Value exn_typ)
+       ~includesSnippets:true ~insertText:"JsExn.throw($0)"
+       ~detail:"Throw any JavaScript value, example: `throw 100`"
+  :: completions_from_cmt
+
 (** Completions intended for piping, from a completion path. *)
 let completionsForPipeFromCompletionPath ~envCompletionIsMadeFrom ~opens ~pos
     ~scope ~debug ~prefix ~env ~rawOpens ~full completionPath =
@@ -1010,7 +1042,7 @@ and getCompletionsForContextPath ~debug ~full ~opens ~rawOpens ~pos ~env ~exact
     | Some (Tpromise (env, typ), _env) ->
       [Completion.create "dummy" ~env ~kind:(Completion.Value typ)]
     | _ -> [])
-  | CPId {path; completionContext; loc} ->
+  | CPId {path; completionContext; loc} -> (
     if Debug.verbose () then print_endline "[ctx_path]--> CPId";
     (* Looks up the type of an identifier.
 
@@ -1048,7 +1080,10 @@ and getCompletionsForContextPath ~debug ~full ~opens ~rawOpens ~pos ~env ~exact
         | _ -> byPath
       else byPath
     in
-    result
+    match (result, path) with
+    | [], [prefix] when Utils.startsWith "throw" prefix ->
+      completionsForThrow ~env ~full
+    | _ -> result)
   | CPApply (cp, labels) -> (
     if Debug.verbose () then print_endline "[ctx_path]--> CPApply";
     match

analysis/src/ProcessCmt.ml

@@ -793,3 +793,77 @@ let fileForModule moduleName ~package =
   | None ->
     Log.log ("No path for module " ^ moduleName);
     None
+
+(* Collect top-level exception constructors from typedtree/CMT file. *)
+let exceptionsForCmt ~cmt : (string * bool) list =
+  match Shared.tryReadCmt cmt with
+  | None -> []
+  | Some infos ->
+    let by_name : (string, bool) Hashtbl.t = Hashtbl.create 16 in
+    let add_ext (ext : Typedtree.extension_constructor) : unit =
+      let name = ext.ext_name.txt in
+      let hasArgs =
+        match ext.ext_kind with
+        | Text_decl (Cstr_tuple args, _ret) -> args <> []
+        | Text_decl (Cstr_record fields, _ret) -> fields <> []
+        | Text_rebind _ -> true
+      in
+      let prev =
+        match Hashtbl.find_opt by_name name with
+        | Some b -> b
+        | None -> false
+      in
+      Hashtbl.replace by_name name (prev || hasArgs)
+    in
+    (* Only collect top-level exception declarations (Tstr_exception/Tsig_exception).
+     Avoid picking up exceptions from Texp_letexception by tracking context. *)
+    let in_toplevel_exception = ref false in
+    let module Iter = TypedtreeIter.MakeIterator (struct
+      include TypedtreeIter.DefaultIteratorArgument
+
+      let enter_structure_item (item : Typedtree.structure_item) =
+        (match item.str_desc with
+        | Tstr_exception _ -> in_toplevel_exception := true
+        | _ -> ());
+        ()
+
+      let leave_structure_item (_ : Typedtree.structure_item) =
+        in_toplevel_exception := false
+
+      let enter_signature_item (item : Typedtree.signature_item) =
+        (match item.sig_desc with
+        | Tsig_exception _ -> in_toplevel_exception := true
+        | _ -> ());
+        ()
+
+      let leave_signature_item (_ : Typedtree.signature_item) =
+        in_toplevel_exception := false
+
+      let enter_extension_constructor (ext : Typedtree.extension_constructor) =
+        if !in_toplevel_exception then add_ext ext
+    end) in
+    let () =
+      match infos.cmt_annots with
+      | Cmt_format.Implementation s -> Iter.iter_structure s
+      | Interface s -> Iter.iter_signature s
+      | Partial_implementation parts ->
+        Array.iter
+          (function
+            | Cmt_format.Partial_structure s -> Iter.iter_structure s
+            | Partial_structure_item si -> Iter.iter_structure_item si
+            | Partial_signature s -> Iter.iter_signature s
+            | Partial_signature_item si -> Iter.iter_signature_item si
+            | _ -> ())
+          parts
+      | Partial_interface parts ->
+        Array.iter
+          (function
+            | Cmt_format.Partial_structure s -> Iter.iter_structure s
+            | Partial_structure_item si -> Iter.iter_structure_item si
+            | Partial_signature s -> Iter.iter_signature s
+            | Partial_signature_item si -> Iter.iter_signature_item si
+            | _ -> ())
+          parts
+      | _ -> ()
+    in
+    Hashtbl.fold (fun name hasArgs acc -> (name, hasArgs) :: acc) by_name []

tests/analysis_tests/tests/src/Throw.res

@@ -0,0 +1,5 @@
+exception MyCustomThingToThrow(string)
+exception NoArgsToThrow
+
+// let x = () => thro
+//                   ^com

tests/analysis_tests/tests/src/expected/Completion.res.txt

@@ -2147,6 +2147,16 @@ Path T
       "modulePath": "TableclothMap",
       "filePath": "src/Completion.res"
     }
+  }, {
+    "label": "Throw",
+    "kind": 9,
+    "tags": [],
+    "detail": "module Throw",
+    "documentation": null,
+    "data": {
+      "modulePath": "Throw",
+      "filePath": "src/Completion.res"
+    }
   }, {
     "label": "TypeArgCtx",
     "kind": 9,

tests/analysis_tests/tests/src/expected/CompletionJsxProps.res.txt

@@ -97,6 +97,16 @@ Path CompletionSupport.TestComponent.make
       "modulePath": "TableclothMap",
       "filePath": "src/CompletionJsxProps.res"
     }
+  }, {
+    "label": "Throw",
+    "kind": 9,
+    "tags": [],
+    "detail": "module Throw",
+    "documentation": null,
+    "data": {
+      "modulePath": "Throw",
+      "filePath": "src/CompletionJsxProps.res"
+    }
   }, {
     "label": "TypeArgCtx",
     "kind": 9,

tests/analysis_tests/tests/src/expected/Throw.res.txt

@@ -0,0 +1,45 @@
+Complete src/Throw.res 3:21
+posCursor:[3:21] posNoWhite:[3:20] Found expr:[3:11->3:21]
+posCursor:[3:21] posNoWhite:[3:20] Found expr:[3:17->3:21]
+Pexp_ident thro:[3:17->3:21]
+Completable: Cpath Value[thro]
+Package opens Stdlib.place holder Pervasives.JsxModules.place holder
+Resolved opens 1 Stdlib
+ContextPath Value[thro]
+Path thro
+[{
+    "label": "JsError.throwWithMessage",
+    "kind": 12,
+    "tags": [],
+    "detail": "Throw a JavaScript error, example: `throw new Error(str)`",
+    "documentation": null,
+    "insertText": "JsError.throwWithMessage(\"$0\")",
+    "insertTextFormat": 2
+  }, {
+    "label": "JsExn.throw",
+    "kind": 12,
+    "tags": [],
+    "detail": "Throw any JavaScript value, example: `throw 100`",
+    "documentation": null,
+    "insertText": "JsExn.throw($0)",
+    "insertTextFormat": 2
+  }, {
+    "label": "throw(MyCustomThingToThrow)",
+    "kind": 12,
+    "tags": [],
+    "detail": "exn",
+    "documentation": null,
+    "filterText": "throw",
+    "insertText": "throw(MyCustomThingToThrow($0))",
+    "insertTextFormat": 2
+  }, {
+    "label": "throw(NoArgsToThrow)",
+    "kind": 12,
+    "tags": [],
+    "detail": "exn",
+    "documentation": null,
+    "filterText": "throw",
+    "insertText": "throw(NoArgsToThrow)",
+    "insertTextFormat": 2
+  }]
+