Format library types as F# abbreviations (Experiment/wip)

src/Compiler/Checking/NicePrint.fs

@@ -978,6 +978,12 @@ module PrintTypes =
             let prefix = usePrefix denv tc
             layoutTypeAppWithInfoAndPrec denv env (layoutTyconRefImpl false denv tc None) prec prefix args
         | TType_app (tc, args, nullness) ->
+            let tc =
+                if tyconRefEq denv.g tc denv.g.tcref_System_Collections_Generic_IEnumerable then
+                    denv.g.seq_tcr
+                else
+                    tc
+
             let prefix = usePrefix denv tc
             let demangledCompilationPathOpt, args =
                 if not denv.includeStaticParametersInTypeNames then

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/Symbols.fs

@@ -521,6 +521,18 @@ 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("IEnumerable<int>", "int seq")>]
+    let ``Format IEnumerable as seq`` declaredType formattedType =
+        let _, checkResults = getParseAndCheckResults $"""
+open System.Collections.Generic
+let f (x: {declaredType}) = ()
 """
         let symbolUse = findSymbolUseByName "x" checkResults
         let symbol = symbolUse.Symbol :?> FSharpMemberOrFunctionOrValue