function implicit conversion the same way as fun x

docs/release-notes/.FSharp.Compiler.Service/9.0.100.md

@@ -5,6 +5,7 @@
 * Optimize simple mappings in comprehensions when the body of the mapping has `let`-bindings and/or sequential expressions before a single yield. ([PR #17419](https://github.com/dotnet/fsharp/pull/17419))
 * C# protected property can be assigned in F# inherit constructor call. ([Issue #13299](https://github.com/dotnet/fsharp/issues/13299), [PR #17391](https://github.com/dotnet/fsharp/pull/17391))
 * MethodAccessException on equality comparison of a record with private fields. ([Issue #17447](https://github.com/dotnet/fsharp/issues/17447), [PR #17391](https://github.com/dotnet/fsharp/pull/17467))
+* Fix `function` implicit conversion. ([Issue #7401](https://github.com/dotnet/fsharp/issues/7401), [PR #17487](https://github.com/dotnet/fsharp/pull/17487))
 
 ### Added
 

src/Compiler/Checking/Expressions/CheckExpressions.fs

@@ -9684,7 +9684,8 @@ and GetNewInferenceTypeForMethodArg (cenv: cenv) env tpenv x =
     | SynExpr.AddressOf (true, a, _, m) ->
         mkByrefTyWithInference g (GetNewInferenceTypeForMethodArg cenv env tpenv a) (NewByRefKindInferenceType g m)
     | SynExpr.Lambda (body = a)
-    | SynExpr.DotLambda (expr = a) ->
+    | SynExpr.DotLambda (expr = a)
+    | SynExpr.MatchLambda (matchClauses = SynMatchClause (resultExpr = a) :: _) ->
         mkFunTy g (NewInferenceType g) (GetNewInferenceTypeForMethodArg cenv env tpenv a)
     | SynExpr.Quote (_, raw, a, _, _) ->
         if raw then mkRawQuotedExprTy g

tests/FSharp.Compiler.ComponentTests/Conformance/BasicGrammarElements/MemberDefinitions/OverloadingMembers/OverloadResolutionUsingFunction.fs

@@ -0,0 +1,28 @@
+open System
+let ae = new AggregateException()
+
+ae.Handle(fun e ->
+    match e with
+    | :? OperationCanceledException -> true
+    | _ -> false        
+    )
+
+ae.Handle(function
+    | :? OperationCanceledException -> true
+    | _ -> false        
+    )
+
+ae.Handle(
+    Func<exn,bool>(
+        function
+        | :? OperationCanceledException -> true
+        | _ -> false        
+    ))
+
+let m () =
+    fun x ->(function x -> function y -> function z -> <@ x + y + z @>)
+
+let f () = 
+    (function
+        | None -> fun x -> x + 2
+        | Some f -> f)

tests/FSharp.Compiler.ComponentTests/Conformance/BasicGrammarElements/MemberDefinitions/OverloadingMembers/OverloadingMembers.fs

@@ -229,3 +229,9 @@ module MemberDefinitions_OverloadingMembers =
         |> withDefines ["TOO_GENERIC"]
         |> verifyCompileAndRun
         |> shouldSucceed
+
+    [<Theory; Directory(__SOURCE_DIRECTORY__, Includes=[|"OverloadResolutionUsingFunction.fs"|])>]
+    let ``OverloadResolutionUsingFunction_fs`` compilation =
+        compilation
+        |> verifyCompileAndRun
+        |> shouldSucceed