Don't consider seq`1 prefix in NicePrint.

Author: nojaf

src/Compiler/Checking/NicePrint.fs

@@ -164,7 +164,7 @@ module internal PrintUtilities =
 
     let usePrefix (denv: DisplayEnv) (tcref: TyconRef) =
         match denv.genericParameterStyle with
-        | GenericParameterStyle.Implicit -> tcref.IsPrefixDisplay
+        | GenericParameterStyle.Implicit -> not (isSeqTyconRef denv.g tcref) && tcref.IsPrefixDisplay
         | GenericParameterStyle.Prefix -> true
         | GenericParameterStyle.Suffix -> false
 

src/Compiler/TypedTree/TypedTreeOps.fs

@@ -1749,6 +1749,9 @@ let isArrayTyconRef (g: TcGlobals) tcref =
     g.il_arr_tcr_map
     |> Array.exists (tyconRefEq g tcref)
 
+let isSeqTyconRef (g: TcGlobals) tcref =
+    tyconRefEq g g.seq_tcr tcref
+
 let rankOfArrayTyconRef (g: TcGlobals) tcref =
     match g.il_arr_tcr_map |> Array.tryFindIndex (tyconRefEq g tcref) with
     | Some idx ->

src/Compiler/TypedTree/TypedTreeOps.fsi

@@ -1618,6 +1618,9 @@ val mkArrayTy: TcGlobals -> int -> TType -> range -> TType
 /// Check if a type definition is one of the artificial type definitions used for array types of different ranks
 val isArrayTyconRef: TcGlobals -> TyconRef -> bool
 
+/// Check if a type definition is of Microsoft.FSharp.Collections.seq`1
+val isSeqTyconRef: TcGlobals -> TyconRef -> bool
+
 /// Determine the rank of one of the artificial type definitions used for array types
 val rankOfArrayTyconRef: TcGlobals -> TyconRef -> int
 

tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj

@@ -244,6 +244,7 @@
     <Compile Include="Signatures\ModuleOrNamespaceTests.fs" />
     <Compile Include="Signatures\RecordTests.fs" />
     <Compile Include="Signatures\ArrayTests.fs" />
+    <Compile Include="Signatures\SeqTests.fs" />
     <Compile Include="Signatures\TypeTests.fs" />
     <Compile Include="Signatures\SigGenerationRoundTripTests.fs" />
     <Compile Include="StaticLinking\StaticLinking.fs" />

tests/FSharp.Compiler.ComponentTests/Signatures/SeqTests.fs

@@ -0,0 +1,10 @@
+module FSharp.Compiler.ComponentTests.Signatures.SeqTests
+
+open Xunit
+open FSharp.Compiler.ComponentTests.Signatures.TestHelpers
+
+[<Fact>]
+let ``int seq`` () =
+    assertSingleSignatureBinding
+        "let s = seq { yield 1 }"
+        "val s: int seq"