Don't consider seq`1 prefix in NicePrint.

src/Compiler/Driver/CompilerImports.fs

@@ -2009,6 +2009,9 @@ and [<Sealed>] TcImports
 
                 let minfo: PickledCcuInfo = data.RawData
                 let mspec = minfo.mspec
+
+                if mspec.DisplayName = "FSharp.Core" then
+                    updateSeqTypeIsPrefix mspec
 
 #if !NO_TYPEPROVIDERS
                 let invalidateCcu = Event<_>()

src/Compiler/TypedTree/TypedTreeOps.fs

@@ -10607,3 +10607,29 @@ let rec serializeEntity path (entity: Entity) =
     let json = sw.ToString()
     use out = FileSystem.OpenFileForWriteShim(path, fileMode = System.IO.FileMode.Create)
     out.WriteAllText(json)
+
+let updateSeqTypeIsPrefix (fsharpCoreMSpec: ModuleOrNamespace) =
+    let findModuleOrNamespace (name: string) (entity: Entity) =
+        if not entity.IsModuleOrNamespace then
+            None
+        else
+            entity.ModuleOrNamespaceType.ModulesAndNamespacesByDemangledName
+            |> Map.tryFind name
+
+    findModuleOrNamespace "Microsoft" fsharpCoreMSpec
+    |> Option.bind (findModuleOrNamespace "FSharp")
+    |> Option.bind (findModuleOrNamespace "Collections")
+    |> Option.iter (fun collectionsEntity ->
+        collectionsEntity.ModuleOrNamespaceType.AllEntitiesByLogicalMangledName
+        |> Map.tryFind "seq`1"
+        |> Option.iter (fun seqEntity ->
+            seqEntity.entity_flags <-
+                EntityFlags(
+                    false,
+                    seqEntity.entity_flags.IsModuleOrNamespace,
+                    seqEntity.entity_flags.PreEstablishedHasDefaultConstructor,
+                    seqEntity.entity_flags.HasSelfReferentialConstructor,
+                    seqEntity.entity_flags.IsStructRecordOrUnionType
+                )
+        )
+    )

src/Compiler/TypedTree/TypedTreeOps.fsi

@@ -2701,3 +2701,7 @@ val tryAddExtensionAttributeIfNotAlreadyPresent:
 
 /// Serialize an entity to a very basic json structure.
 val serializeEntity: path: string -> entity: Entity -> unit
+
+/// Updates the IsPrefixDisplay to false for the Microsoft.FSharp.Collections.seq`1 entity
+/// Meant to be called with the FSharp.Core module spec right after it was unpickled.
+val updateSeqTypeIsPrefix: fsharpCoreMSpec: ModuleOrNamespace -> unit

tests/FSharp.Compiler.ComponentTests/CompilerOptions/fsc/flaterrors.fs

@@ -26,8 +26,8 @@ module flaterrors =
         |> compile options
         |> shouldFail
         |> withDiagnostics [
-            (Error 1, Line 1, Col 11, Line 1, Col 16, "This expression was expected to have type\n    ''a list'    \nbut here has type\n    'seq<'b>'    ")
-            (Error 1, Line 1, Col 11, Line 1, Col 16, "This expression was expected to have type\n    ''a list'    \nbut here has type\n    'seq<int>'    ")
+            (Error 1, Line 1, Col 11, Line 1, Col 16, "This expression was expected to have type\n    ''a list'    \nbut here has type\n    ''b seq'    ")
+            (Error 1, Line 1, Col 11, Line 1, Col 16, "This expression was expected to have type\n    ''a list'    \nbut here has type\n    'int seq'    ")
             (Warning 20, Line 1, Col 1, Line 1, Col 17, "The result of this expression has type ''a list' and is implicitly ignored. Consider using 'ignore' to discard this value explicitly, e.g. 'expr |> ignore', or 'let' to bind the result to a name, e.g. 'let result = expr'.")
         ]
 
@@ -40,8 +40,8 @@ module flaterrors =
         |> compile options
         |> shouldFail
         |> withDiagnostics [
-            (Error 1, Line 1, Col 11, Line 1, Col 16, "This expression was expected to have type\029    ''a list'    \029but here has type\029    'seq<'b>'")
-            (Error 1, Line 1, Col 11, Line 1, Col 16, "This expression was expected to have type\029    ''a list'    \029but here has type\029    'seq<int>'")
+            (Error 1, Line 1, Col 11, Line 1, Col 16, "This expression was expected to have type\029    ''a list'    \029but here has type\029    ''b seq'")
+            (Error 1, Line 1, Col 11, Line 1, Col 16, "This expression was expected to have type\029    ''a list'    \029but here has type\029    'int seq'")
         ]
 
     [<InlineData("--flaterrors")>]                          //once

tests/FSharp.Compiler.ComponentTests/ConstraintSolver/neg_invalid_constructor.fs.err.bsl

@@ -17,6 +17,6 @@ neg_invalid_constructor.fs (7,30)-(7,60) typecheck error A unique overload for m
 Known type of argument: 'a list
 
 Candidates:
- - new: col: 'b -> ImmutableStack<'a> when 'b :> seq<'c>
+ - new: col: 'b -> ImmutableStack<'a> when 'b :> 'c seq
  - private new: items: 'a list -> ImmutableStack<'a>
 neg_invalid_constructor.fs (7,30)-(7,60) typecheck error This is not a valid object construction expression. Explicit object constructors must either call an alternate constructor or initialize all fields of the object and specify a call to a super class constructor.

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

@@ -246,6 +246,7 @@
     <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="Signatures\NestedTypeTests.fs" />

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

@@ -0,0 +1,16 @@
+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"
+
+[<Fact>]
+let ``tuple seq`` () =
+    assertSingleSignatureBinding
+        "let s = seq { yield (1, 'b', 2.) }"
+        "val s: (int * char * float) seq"

tests/fsharp/core/auto-widen/5.0/test.bsl

@@ -664,62 +664,62 @@ but here has type
     'int'    
 
 test.fsx(335,28,335,39): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(337,9,338,34): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(340,9,341,33): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(343,9,344,35): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(346,9,347,36): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(349,9,349,36): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(351,9,351,40): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(353,9,354,40): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(356,9,357,41): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(359,9,359,35): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(361,9,362,36): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
 test.fsx(364,9,365,37): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a list'    
 
@@ -779,72 +779,72 @@ but here has type
     'int'    
 
 test.fsx(390,28,390,41): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(391,30,392,57): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(393,30,394,56): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(395,30,396,58): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(397,30,398,59): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(399,30,399,59): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(400,30,400,63): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(401,30,402,63): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(403,30,404,64): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(405,31,405,59): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(406,31,407,60): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(408,31,409,61): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     ''a array'    
 
 test.fsx(429,10,437,16): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     'OtherSeq<'a>'    
 
 test.fsx(448,9,450,49): typecheck error FS0001: This expression was expected to have type
-    'seq<int64>'    
+    'int64 seq'    
 but here has type
     'OtherSeqImpl<'a>'    
 
@@ -855,5 +855,6 @@ but here has type
 
 test.fsx(454,46,454,47): typecheck error FS0001: This expression was expected to have type
     'int64'    
+    'int64'    
 but here has type
     'int'