fable-compiler · ncave · Nov 15, 2023 · Nov 15, 2023
diff --git a/.vscode/settings.json b/.vscode/settings.json
@@ -23,6 +23,8 @@
         "src/fcs-fable"
     ],
     "rust-analyzer.linkedProjects": [
+        "build/fable-library-rust/Cargo.toml",
+        "build/tests/Rust/Cargo.toml",
         "temp/fable-library-rust/Cargo.toml",
         "temp/tests/Rust/Cargo.toml"
     ],

diff --git a/src/Fable.Cli/CHANGELOG.md b/src/Fable.Cli/CHANGELOG.md
@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+#### All
+
+* Fix #3584: Unit type compiles to undeclared variable (by @ncave)
+
 #### Rust
 
 * Added `Guid.TryParse`, `Guid.ToByteArray` (by @ncave)

diff --git a/src/Fable.Transforms/Dart/Fable2Dart.fs b/src/Fable.Transforms/Dart/Fable2Dart.fs
@@ -110,13 +110,6 @@ module Util =
         let fn = com.GetImportIdent(ctx, memberName, modulePath, Fable.Any)
         Expression.invocationExpression(fn.Expr, args, transformType com ctx t)
 
-    let discardUnitArg (args: Fable.Ident list) =
-        match args with
-        | [] -> []
-        | [unitArg] when unitArg.Type = Fable.Unit -> []
-        | [thisArg; unitArg] when thisArg.IsThisArgument && unitArg.Type = Fable.Unit -> [thisArg]
-        | args -> args
-
     let addErrorAndReturnNull (com: Compiler) (range: SourceLocation option) (error: string) =
         addError com [] range error
         NullLiteral Dynamic |> Literal
@@ -244,8 +237,11 @@ module Util =
     type NamedTailCallOpportunity(_com: IDartCompiler, ctx, name, args: Fable.Ident list) =
         // Capture the current argument values to prevent delayed references from getting corrupted,
         // for that we use block-scoped ES2015 variable declarations. See #681, #1859
-        let argIds = discardUnitArg args |> List.map (fun arg ->
-            getUniqueNameInDeclarationScope ctx (arg.Name + "_mut"))
+        let argIds =
+            args
+            |> FSharp2Fable.Util.discardUnitArg
+            |> List.map (fun arg ->
+                getUniqueNameInDeclarationScope ctx (arg.Name + "_mut"))
         interface ITailCallOpportunity with
             member _.Label = name
             member _.Args = argIds
@@ -359,12 +355,16 @@ module Util =
         statements1 @ statements2 @ [Statement.continueStatement(tc.Label)]
 
     let transformCallArgs (com: IDartCompiler) ctx (info: ArgsInfo) =
+
         let paramsInfo, thisArg, args =
             match info with
-            | NoCallInfo args -> None, None, args
+            | NoCallInfo args ->
+                let args = FSharp2Fable.Util.dropUnitCallArg args []
+                None, None, args
             | CallInfo callInfo ->
+                let args = FSharp2Fable.Util.dropUnitCallArg callInfo.Args callInfo.SignatureArgTypes
                 let paramsInfo = callInfo.MemberRef |> Option.bind com.TryGetMember |> Option.map getParamsInfo
-                paramsInfo, callInfo.ThisArg, callInfo.Args
+                paramsInfo, callInfo.ThisArg, args
 
         let unnamedArgs, namedArgs =
             paramsInfo
@@ -383,7 +383,6 @@ module Util =
 
         let unnamedArgs =
             match unnamedArgs, paramsInfo with
-            | [Fable.Value(Fable.UnitConstant,_)], _ -> []
             | args, Some paramsInfo ->
                 let argsLen = args.Length
                 let parameters = paramsInfo.Parameters
@@ -833,7 +832,10 @@ module Util =
             let invocation =
                 match args with
                 | [] -> Expression.invocationExpression(callee, t)
-                | args -> (callee, args) ||> List.fold (fun e arg -> Expression.invocationExpression(e, [arg], t))
+                | args ->
+                    (callee, args)
+                    ||> List.fold (fun expr arg ->
+                        Expression.invocationExpression(expr, [arg], t))
             let statements2, capturedExpr = resolveExpr returnStrategy invocation
             statements @ statements2, capturedExpr
 
@@ -1062,7 +1064,7 @@ module Util =
         let tailcallChance = Option.map (fun name ->
             NamedTailCallOpportunity(com, ctx, name, args) :> ITailCallOpportunity) name
 
-        let args = discardUnitArg args
+        let args = FSharp2Fable.Util.discardUnitArg args
         let mutable isTailCallOptimized = false
         let varsInScope = args |> List.map (fun a -> a.Name) |> HashSet
         let ctx =

diff --git a/src/Fable.Transforms/FSharp2Fable.Util.fs b/src/Fable.Transforms/FSharp2Fable.Util.fs
@@ -1405,6 +1405,26 @@ module Util =
     open TypeHelpers
     open Identifiers
 
+    let isUnitArg (ident: Fable.Ident) =
+        ident.IsCompilerGenerated
+        && ident.Type = Fable.Unit
+        // && (ident.DisplayName.StartsWith("unitVar") || ident.DisplayName.Contains("@"))
+
+    let discardUnitArg (args: Fable.Ident list) =
+        match args with
+        | [] -> []
+        | [arg] when isUnitArg arg -> []
+        | [thisArg; arg] when thisArg.IsThisArgument && isUnitArg arg -> [thisArg]
+        | args -> args
+
+    let dropUnitCallArg (args: Fable.Expr list) (argTypes: Fable.Type list) =
+        match args, argTypes with
+        // Don't remove unit arg if a generic is expected
+        | [MaybeCasted(Fable.Value(Fable.UnitConstant,_))], [Fable.GenericParam _] -> args
+        | [MaybeCasted(Fable.Value(Fable.UnitConstant,_))], _ -> []
+        | [Fable.IdentExpr ident], _ when isUnitArg ident -> []
+        | _ -> args
+
     let makeFunctionArgs com ctx (args: FSharpMemberOrFunctionOrValue list) =
         let ctx, args =
             ((ctx, []), args)
@@ -2168,10 +2188,10 @@ module Util =
     let makeValueFrom (com: IFableCompiler) (ctx: Context) r (v: FSharpMemberOrFunctionOrValue) =
         let typ = makeType ctx.GenericArgs v.FullType
         match v, v.DeclaringEntity with
-        | _ when typ = Fable.Unit ->
-            if com.Options.Verbosity = Verbosity.Verbose && not v.IsCompilerGenerated then // See #1516
-                $"Value %s{v.DisplayName} is replaced with unit constant"
-                |> addWarning com ctx.InlinePath r
+        | _ when typ = Fable.Unit && v.IsCompilerGenerated ->
+            // if com.Options.Verbosity = Verbosity.Verbose && not v.IsCompilerGenerated then // See #1516
+            //     $"Value %s{v.DisplayName} is replaced with unit constant"
+            //     |> addWarning com ctx.InlinePath r
             Fable.Value(Fable.UnitConstant, r)
         | Emitted com r typ None emitted, _ -> emitted
         | Imported com r typ None imported -> imported

diff --git a/src/Fable.Transforms/Fable2Babel.fs b/src/Fable.Transforms/Fable2Babel.fs
@@ -849,13 +849,6 @@ module Util =
         | Fable.LetRec(bindings, body) -> Some(bindings, body)
         | _ -> None
 
-    let discardUnitArg (args: Fable.Ident list) =
-        match args with
-        | [] -> []
-        | [unitArg] when unitArg.Type = Fable.Unit -> []
-        | [thisArg; unitArg] when thisArg.IsThisArgument && unitArg.Type = Fable.Unit -> [thisArg]
-        | args -> args
-
     let getUniqueNameInRootScope (ctx: Context) name =
         let name = (name, Naming.NoMemberPart) ||> Naming.sanitizeIdent (fun name ->
             ctx.UsedNames.RootScope.Contains(name)
@@ -872,8 +865,11 @@ module Util =
     type NamedTailCallOpportunity(_com: Compiler, ctx, name, args: Fable.Ident list) =
         // Capture the current argument values to prevent delayed references from getting corrupted,
         // for that we use block-scoped ES2015 variable declarations. See #681, #1859
-        let argIds = args |> discardUnitArg |> List.map (fun arg ->
-            getUniqueNameInDeclarationScope ctx (arg.Name + "_mut"))
+        let argIds =
+            args
+            |> FSharp2Fable.Util.discardUnitArg
+            |> List.map (fun arg ->
+                getUniqueNameInDeclarationScope ctx (arg.Name + "_mut"))
         interface ITailCallOpportunity with
             member _.Label = name
             member _.Args = argIds
@@ -1516,13 +1512,8 @@ module Util =
             Expression.newExpression(classExpr, [||])
 
     let transformCallArgs (com: IBabelCompiler) ctx (callInfo: Fable.CallInfo) (memberInfo: Fable.MemberFunctionOrValue option) =
-        let args =
-            match callInfo.Args, callInfo.SignatureArgTypes with
-            // Don't remove unit arg if a generic is expected, TypeScript will complain
-            | [Fable.Value(Fable.UnitConstant,_)], [Fable.GenericParam _] -> callInfo.Args
-            | [Fable.Value(Fable.UnitConstant,_)], _ -> []
-            | _ -> callInfo.Args
 
+        let args = FSharp2Fable.Util.dropUnitCallArg callInfo.Args callInfo.SignatureArgTypes
         let paramsInfo = Option.map getParamsInfo memberInfo
 
         let args =
@@ -1746,14 +1737,14 @@ module Util =
 
     let transformCurriedApply com ctx range (TransformExpr com ctx applied) args =
         (applied, args)
-        ||> List.fold (fun e arg ->
+        ||> List.fold (fun expr arg ->
             match arg with
             // TODO: If arg type is unit but it's an expression with potential
             // side-effects, we need to extract it and execute it before the call
             | Fable.Value(Fable.UnitConstant,_) -> []
             | Fable.IdentExpr ident when ident.Type = Fable.Unit -> []
             | TransformExpr com ctx arg -> [arg]
-            |> callFunction com ctx range e [])
+            |> callFunction com ctx range expr [])
 
     let transformCallAsStatements com ctx range t returnStrategy callee callInfo =
         let argsLen (i: Fable.CallInfo) =
@@ -2402,7 +2393,7 @@ module Util =
         let tailcallChance =
             Option.map (fun name ->
                 NamedTailCallOpportunity(com, ctx, name, args) :> ITailCallOpportunity) name
-        let args = discardUnitArg args
+        let args = FSharp2Fable.Util.discardUnitArg args
         let declaredVars = ResizeArray()
         let mutable isTailCallOptimized = false
         let ctx =
@@ -2883,7 +2874,7 @@ module Util =
                 let args =
                     info.CurriedParameterGroups
                     |> List.concat
-                    // |> discardUnitArg
+                    // |> FSharp2Fable.Util.discardUnitArg
                     |> List.toArray
 
                 let argsLen = Array.length args

diff --git a/src/Fable.Transforms/Python/Fable2Python.fs b/src/Fable.Transforms/Python/Fable2Python.fs
@@ -997,17 +997,6 @@ module Util =
         | Fable.Delegate (args, body, _, []) -> Some(args, body)
         | _ -> None
 
-    let discardUnitArg (args: Fable.Ident list) =
-        match args with
-        | [] -> []
-        | [ unitArg ] when unitArg.Type = Fable.Unit -> []
-        | [ thisArg; unitArg ] when
-            thisArg.IsThisArgument
-            && unitArg.Type = Fable.Unit
-            ->
-            [ thisArg ]
-        | args -> args
-
     let getUniqueNameInRootScope (ctx: Context) name =
         let name =
             (name, Naming.NoMemberPart)
@@ -1036,7 +1025,8 @@ module Util =
         // for that we use block-scoped ES2015 variable declarations. See #681, #1859
         // TODO: Local unique ident names
         let argIds =
-            discardUnitArg args
+            args
+            |> FSharp2Fable.Util.discardUnitArg
             |> List.map (fun arg ->
                 let name = getUniqueNameInDeclarationScope ctx (arg.Name + "_mut")
                 // Ignore type annotation here as it generates unnecessary typevars
@@ -1856,8 +1846,9 @@ module Util =
         Expression.call (Expression.name name), [ stmt ] @ stmts
 
     let transformCallArgs (com: IPythonCompiler) ctx (callInfo: Fable.CallInfo) : Expression list * Keyword list * Statement list =
+
+        let args = FSharp2Fable.Util.dropUnitCallArg callInfo.Args callInfo.SignatureArgTypes
         let paramsInfo = callInfo.MemberRef |> Option.bind com.TryGetMember |> Option.map getParamsInfo
-        let args = callInfo.Args
 
         let args, objArg, stmts =
             paramsInfo
@@ -1890,8 +1881,7 @@ module Util =
 
         let args, stmts' =
             match args with
-            | []
-            | [ MaybeCasted (Fable.Value (Fable.UnitConstant, _)) ] -> [], []
+            | [] -> [], []
             | args when hasSpread ->
                 match List.rev args with
                 | [] -> [], []
@@ -2065,8 +2055,10 @@ module Util =
                 match arg with
                 // TODO: If arg type is unit but it's an expression with potential
                 // side-effects, we need to extract it and execute it before the call
-                | Fable.Value(Fable.UnitConstant,_) -> [], []
-                | Fable.IdentExpr ident when ident.Type = Fable.Unit -> [], []
+
+                // TODO: discardUnitArg may still be needed in some cases
+                // | Fable.Value(Fable.UnitConstant,_) -> [], []
+                // | Fable.IdentExpr ident when ident.Type = Fable.Unit -> [], []
                 | TransformExpr com ctx (arg, stmts') -> [arg], stmts'
             callFunction range applied args [], stmts @ stmts')
 
@@ -3232,7 +3224,7 @@ module Util =
         let tailcallChance =
             Option.map (fun name -> NamedTailCallOpportunity(com, ctx, name, args) :> ITailCallOpportunity) name
 
-        let args = discardUnitArg args
+        let args = FSharp2Fable.Util.discardUnitArg args
 
         /// Removes `_mut` or `_mut_1` suffix from the identifier name
         let cleanName (input: string) = Regex.Replace(input, @"_mut(_\d+)?$", "")

diff --git a/src/Fable.Transforms/Rust/Fable2Rust.fs b/src/Fable.Transforms/Rust/Fable2Rust.fs
@@ -1158,24 +1158,19 @@ module Util =
         | _ -> None
 
     let isUnitArg (ident: Fable.Ident) =
-        ident.IsCompilerGenerated &&
-        ident.Type = Fable.Unit &&
-        (ident.DisplayName.StartsWith("unitVar") || ident.DisplayName.Contains("@"))
+        ident.IsCompilerGenerated
+        && ident.Type = Fable.Unit
+        && (ident.DisplayName.StartsWith("unitVar") || ident.DisplayName.Contains("@"))
 
     let discardUnitArg (genArgs: Fable.Type list) (args: Fable.Ident list) =
         match genArgs, args with
         | [Fable.Unit], [arg] -> args // don't drop unit arg when generic arg is unit
-        | _, [] -> []
-        | _, [arg] when isUnitArg arg -> []
-        | _, [thisArg; arg] when thisArg.IsThisArgument && isUnitArg arg -> [thisArg]
-        | _, args -> args
-
-    let dropUnitCallArg (genArgs: Fable.Type list) (args: Fable.Expr list) =
-        match genArgs, args with
-        | [Fable.Unit], [arg] -> args // don't drop unit arg when generic arg is unit
-        | _, [MaybeCasted(Fable.Value(Fable.UnitConstant, _))] -> []
-        | _, [Fable.IdentExpr ident] when isUnitArg ident -> []
-        | _, args -> args
+        | _ ->
+            match args with
+            | [] -> []
+            | [arg] when isUnitArg arg -> []
+            | [thisArg; arg] when thisArg.IsThisArgument && isUnitArg arg -> [thisArg]
+            | args -> args
 
     /// Fable doesn't currently sanitize attached members/fields so we do a simple sanitation here.
     /// Should this be done in FSharp2Fable step?
@@ -2151,7 +2146,7 @@ module Util =
             { ctx with RequiresSendSync = isSendSync
                        IsParamByRefPreferred = isByRefPreferred }
 
-        let args = dropUnitCallArg callInfo.GenericArgs callInfo.Args
+        let args = FSharp2Fable.Util.dropUnitCallArg callInfo.Args callInfo.SignatureArgTypes
         let args = transformCallArgs com ctx args callInfo.SignatureArgTypes argParams
 
         match calleeExpr with
@@ -2622,9 +2617,10 @@ module Util =
             optimizeTailCall com ctx r tc args
         | _ ->
             let callee = transformCallee com ctx calleeExpr
-            (callee, args) ||> List.fold (fun c arg ->
-                let args = dropUnitCallArg [] [arg]
-                callFunction com ctx r c args)
+            (callee, args)
+            ||> List.fold (fun expr arg ->
+                let args = FSharp2Fable.Util.dropUnitCallArg [arg] []
+                callFunction com ctx r expr args)
 
     let makeUnionCasePat unionCaseName fields =
         if List.isEmpty fields then

diff --git a/tests/Dart/src/ArrayTests.fs b/tests/Dart/src/ArrayTests.fs
@@ -285,7 +285,7 @@ let tests () =
         ys.[0] + ys.[1]
         |> equal 3.
 
-    testCase "Array.concat works with strings" <| fun test ->
+    testCase "Array.concat works with strings" <| fun () ->
         [| [| "One" |]; [| "Two" |] |]
         |> Array.concat
         |> List.ofArray

diff --git a/tests/Js/Main/ArrayTests.fs b/tests/Js/Main/ArrayTests.fs
@@ -361,7 +361,7 @@ let tests =
         ys.[0] + ys.[1]
         |> equal 3.
 
-    testCase "Array.concat works with strings" <| fun test ->
+    testCase "Array.concat works with strings" <| fun () ->
         [| [| "One" |]; [| "Two" |] |]
         |> Array.concat
         |> List.ofArray

diff --git a/tests/Js/Main/MiscTests.fs b/tests/Js/Main/MiscTests.fs
@@ -385,7 +385,7 @@

 let mutable mutableValue = 0

 let rec recursive1 = delay (fun () -> recursive2())
 and recursive2 =
    mutableValue <- 5
    fun () -> mutableValue <- mutableValue * 2
@@ -477,9 +477,17 @@
 
 let sideEffect() = ()
 
+let inline inlineToString (f: 'T -> string): 'T -> string =
+    let unused = f
+    fun a -> $"{a}"
+
 let tests =
   testList "Miscellaneous" [
 
+    testCase "Generic unit args work" <| fun _ -> // #3584
+        let to_str = inlineToString (fun (props: unit) -> "s")
+        to_str () |> equal $"{()}"
+
 #if FABLE_COMPILER
 #if !FABLE_COMPILER_JAVASCRIPT
     testCase "Fable.JsonProvider works" <| fun _ ->
@@ -1069,7 +1077,7 @@
        | 2 -> x <- "2"
        | 3 | 4 -> x <- "3" // Multiple cases are allowed
        // | 5 | 6 as j -> x <- string j // This prevents the optimization
        | 4 -> x <- "4" // Unreachable cases are removed
        | _ -> x <- "?"
        equal "3" x