Import IEnumerable as seq

docs/release-notes/.FSharp.Compiler.Service/10.0.100.md

@@ -31,6 +31,7 @@
 * Use `errorR` instead of `error` in `CheckDeclarations.fs` when possible. ([PR #18645](https://github.com/dotnet/fsharp/pull/18645))
 * Parser: Capture named fields block separators. ([PR #18857](https://github.com/dotnet/fsharp/pull/18857))
 * Type checker: use inner expr range in upcast constraints errors ([PR #18850](https://github.com/dotnet/fsharp/pull/18850))
+* Import `IEnumerable` as `seq`. ([PR #18865](https://github.com/dotnet/fsharp/pull/18865))
 * Parser: Capture multiple block separators ([PR #18899](https://github.com/dotnet/fsharp/pull/18899))
 
 ### Breaking Changes

src/Compiler/TypedTree/TcGlobals.fs

@@ -966,30 +966,33 @@ type TcGlobals(
   let mkDebuggerTypeProxyAttribute (ty : ILType) = mkILCustomAttribute (findSysILTypeRef tname_DebuggerTypeProxyAttribute,  [ilg.typ_Type], [ILAttribElem.TypeRef (Some ty.TypeRef)], [])
 
   let betterTyconEntries =
-     [| "Int32"    , v_int_tcr
-        "IntPtr"   , v_nativeint_tcr
-        "UIntPtr"  , v_unativeint_tcr
-        "Int16"    , v_int16_tcr
-        "Int64"    , v_int64_tcr
-        "UInt16"   , v_uint16_tcr
-        "UInt32"   , v_uint32_tcr
-        "UInt64"   , v_uint64_tcr
-        "SByte"    , v_sbyte_tcr
-        "Decimal"  , v_decimal_tcr
-        "Byte"     , v_byte_tcr
-        "Boolean"  , v_bool_tcr
-        "String"   , v_string_tcr
-        "Object"   , v_obj_tcr
-        "Exception", v_exn_tcr
-        "Char"     , v_char_tcr
-        "Double"   , v_float_tcr
-        "Single"   , v_float32_tcr |]
-            |> Array.map (fun (nm, tcr) ->
+     [| yield sys, "Int32"    , v_int_tcr
+        yield sys, "IntPtr"   , v_nativeint_tcr
+        yield sys, "UIntPtr"  , v_unativeint_tcr
+        yield sys, "Int16"    , v_int16_tcr
+        yield sys, "Int64"    , v_int64_tcr
+        yield sys, "UInt16"   , v_uint16_tcr
+        yield sys, "UInt32"   , v_uint32_tcr
+        yield sys, "UInt64"   , v_uint64_tcr
+        yield sys, "SByte"    , v_sbyte_tcr
+        yield sys, "Decimal"  , v_decimal_tcr
+        yield sys, "Byte"     , v_byte_tcr
+        yield sys, "Boolean"  , v_bool_tcr
+        yield sys, "String"   , v_string_tcr
+        yield sys, "Object"   , v_obj_tcr
+        yield sys, "Exception", v_exn_tcr
+        yield sys, "Char"     , v_char_tcr
+        yield sys, "Double"   , v_float_tcr
+        yield sys, "Single"   , v_float32_tcr
+        if not compilingFSharpCore then
+            yield sysGenerics, "IEnumerable`1", v_seq_tcr |]
+            |> Array.map (fun (qualifier, nm, tcr) ->
                 let ty = mkNonGenericTy tcr
-                nm, findSysTyconRef sys nm, (fun _ nullness ->
-                    match nullness with
-                    | Nullness.Known NullnessInfo.WithoutNull -> ty
-                    | _ -> mkNonGenericTyWithNullness tcr nullness))
+                nm, findSysTyconRef qualifier nm, (fun typars nullness ->
+                    match typars, nullness with
+                    | [], Nullness.Known NullnessInfo.WithoutNull -> ty
+                    | [], nullness -> mkNonGenericTyWithNullness tcr nullness
+                    | _ -> TType_app(tcr, typars, nullness)))
 
   let decompileTyconEntries =
         [|

tests/FSharp.Compiler.Service.Tests/EditorTests.fs

@@ -130,15 +130,15 @@ let ``GetMethodsAsSymbols should return all overloads of a method as FSharpSymbo
                 yield ms.Symbol.DisplayName, extractCurriedParams ms ]
             |> List.sortBy (fun (_name, parameters) -> parameters.Length, (parameters |> List.map snd ))
         let expected =
-            [("Concat", [("values", "Collections.Generic.IEnumerable<'T>")]);
-             ("Concat", [("values", "Collections.Generic.IEnumerable<string>")]);
+            [("Concat", [("values", "'T seq")]);
 #if NETCOREAPP
              ("Concat", [("args", "ReadOnlySpan<obj>")]);
              ("Concat", [("values", "ReadOnlySpan<string>")]);
 #endif
              ("Concat", [("arg0", "obj")]);
              ("Concat", [("args", "obj array")]);
-             ("Concat", [("values", "string array")]);
+             ("Concat", [("values", "string array")])
+             ("Concat", [("values", "string seq")])
 #if NETCOREAPP
              ("Concat", [("str0", "ReadOnlySpan<char>");("str1", "ReadOnlySpan<char>")]);
 #endif

tests/FSharp.Compiler.Service.Tests/ProjectAnalysisTests.fs

@@ -3216,7 +3216,7 @@ let ``Test Project22 IList contents`` () =
     set [ for x in ilistTypeDefn.AllInterfaces -> x.TypeDefinition.DisplayName, attribsOfSymbol x.TypeDefinition ]
        |> shouldEqual
               (set [("IList", ["interface"]); ("ICollection", ["interface"]);
-                    ("IEnumerable", ["interface"]); ("IEnumerable", ["interface"])])
+                    ("IEnumerable", ["interface"]); ("seq", ["abbrev"])])
 
     arrayTypes |> shouldEqual [|("[]", 1); ("[,,]", 3)|]
 

tests/FSharp.Compiler.Service.Tests/Symbols.fs

@@ -521,6 +521,20 @@ let f2 b1 b2 b3 b4 b5 =
     let ``Nullable types`` declaredType formattedType =
         let _, checkResults = getParseAndCheckResults $"""
 let f (x: {declaredType}) = ()
+"""
+        let symbolUse = findSymbolUseByName "x" checkResults
+        let symbol = symbolUse.Symbol :?> FSharpMemberOrFunctionOrValue
+        let typeArg = symbol.FullType
+        typeArg.Format(symbolUse.DisplayContext) |> shouldEqual formattedType
+
+    [<Theory>]
+    [<InlineData("let x: IEnumerable<int> = []", "IEnumerable<int>")>]
+    [<InlineData("let x = [1].AsEnumerable()", "int seq")>]
+    let ``Format IEnumerable`` code formattedType =
+        let _, checkResults = getParseAndCheckResults $"""
+open System.Collections.Generic
+open System.Linq
+{code}
 """
         let symbolUse = findSymbolUseByName "x" checkResults
         let symbol = symbolUse.Symbol :?> FSharpMemberOrFunctionOrValue

vsintegration/tests/FSharp.Editor.Tests/QuickInfoProviderTests.fs

@@ -226,7 +226,7 @@ let res8 = abs 5.0<kg>
             [
                 mkDesc
                     "GroupBy"
-                    "(extension) System.Collections.Generic.IEnumerable.GroupBy<'TSource,'TKey>(keySelector: System.Func<'TSource,'TKey>) : System.Collections.Generic.IEnumerable<IGrouping<'TKey,'TSource>>
+                    "(extension) System.Collections.Generic.IEnumerable.GroupBy<'TSource,'TKey>(keySelector: System.Func<'TSource,'TKey>) : IGrouping<'TKey,'TSource> seq
 'TSource is int * string
 'TKey is int"
                 mkDesc

vsintegration/tests/FSharp.Editor.Tests/Refactors/AddReturnTypeTests.fs

@@ -298,7 +298,7 @@ let ``Binding linq function doesnt crash`` () =
     let code =
         $"""
 let skip1 elements = 
-    System.Linq.Enumerable.Skip(elements, 1)
+    System.Linq.Enumerable.Skip(elements, 1).GetEnumerator()
         """
 
     use context = TestContext.CreateWithCode code
@@ -309,8 +309,8 @@ let skip1 elements =
 
     let expectedCode =
         $"""
-let skip1 elements : System.Collections.Generic.IEnumerable<'a> = 
-    System.Linq.Enumerable.Skip(elements, 1)
+let skip1 elements : System.Collections.Generic.IEnumerator<'a> = 
+    System.Linq.Enumerable.Skip(elements, 1).GetEnumerator()
         """
 
     let resultText = newDoc.GetTextAsync() |> GetTaskResult
@@ -325,7 +325,7 @@ let ``Handle already existing opens on Linq`` () =
 open System
 
 let skip1 elements = 
-    Linq.Enumerable.Skip(elements, 1)
+    Linq.Enumerable.Skip(elements, 1).GetEnumerator()
         """
 
     use context = TestContext.CreateWithCode code
@@ -338,8 +338,8 @@ let skip1 elements =
         $"""
 open System
 
-let skip1 elements : Collections.Generic.IEnumerable<'a> = 
-    Linq.Enumerable.Skip(elements, 1)
+let skip1 elements : Collections.Generic.IEnumerator<'a> = 
+    Linq.Enumerable.Skip(elements, 1).GetEnumerator()
         """
 
     let resultText = newDoc.GetTextAsync() |> GetTaskResult
@@ -355,7 +355,7 @@ open System
 open System.Linq
 
 let skip1 elements = 
-    Enumerable.Skip(elements, 1)
+    Enumerable.Skip(elements, 1).GetEnumerator()
         """
 
     use context = TestContext.CreateWithCode code
@@ -369,8 +369,37 @@ let skip1 elements =
 open System
 open System.Linq
 
-let skip1 elements : Collections.Generic.IEnumerable<'a> = 
-    Enumerable.Skip(elements, 1)
+let skip1 elements : Collections.Generic.IEnumerator<'a> = 
+    Enumerable.Skip(elements, 1).GetEnumerator()
+        """
+
+    let resultText = newDoc.GetTextAsync() |> GetTaskResult
+    Assert.Equal(expectedCode, resultText.ToString())
+
+[<Fact>]
+let ``Handle seq`` () =
+    let symbolName = "skip1"
+
+    let code =
+        $"""
+open System
+
+let skip1 elements =
+    Linq.Enumerable.Skip(elements, 1)
+        """
+
+    use context = TestContext.CreateWithCode code
+
+    let spanStart = code.IndexOf symbolName
+
+    let newDoc = tryRefactor code spanStart context (new AddReturnType())
+
+    let expectedCode =
+        $"""
+open System
+
+let skip1 elements : 'a seq =
+    Linq.Enumerable.Skip(elements, 1)
         """
 
     let resultText = newDoc.GetTextAsync() |> GetTaskResult