From f96e69f0641bb5702291cf3d0e6b07f6c464a4c7 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 18 May 2026 11:21:57 +0000
Subject: [PATCH 1/2] Initial plan


From 150a7cd21332f6906ac286306a7847290c618c2f Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 18 May 2026 11:51:26 +0000
Subject: [PATCH 2/2] Fix SRTP get_Item witness handling for string indexers

Agent-Logs-Url: https://github.com/dotnet/fsharp/sessions/c94502d3-ac80-4c41-af0e-ebfe0317394b

Co-authored-by: T-Gro <46543583+T-Gro@users.noreply.github.com>
---
 src/Compiler/TypedTree/TcGlobals.fs           |  2 +-
 .../IWSAMsAndSRTPs/IWSAMsAndSRTPsTests.fs     | 20 ++++++++++++++++++-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/Compiler/TypedTree/TcGlobals.fs b/src/Compiler/TypedTree/TcGlobals.fs
index ef6e00ffb16..6dfbd42f98c 100644
--- a/src/Compiler/TypedTree/TcGlobals.fs
+++ b/src/Compiler/TypedTree/TcGlobals.fs
@@ -1929,7 +1929,7 @@ type TcGlobals(
         Some (g.array_get_info, [retTy], argExprs)
     | "set_Item", [arrTy; _; elemTy], _, [_; _; _] when isArrayTy g arrTy ->
         Some (g.array_set_info, [elemTy], argExprs)
-    | "get_Item", [stringTy; _; _], _, [_; _] when isStringTy g stringTy ->
+    | "get_Item", [stringTy; _], _, [_; _] when isStringTy g stringTy ->
         Some (g.getstring_info, [], argExprs)
     | "op_UnaryPlus", [aty], _, [_] ->
         // Call Operators.id
diff --git a/tests/FSharp.Compiler.ComponentTests/Conformance/Types/TypeConstraints/IWSAMsAndSRTPs/IWSAMsAndSRTPsTests.fs b/tests/FSharp.Compiler.ComponentTests/Conformance/Types/TypeConstraints/IWSAMsAndSRTPs/IWSAMsAndSRTPsTests.fs
index 2fd70fab940..fb6c648ca49 100644
--- a/tests/FSharp.Compiler.ComponentTests/Conformance/Types/TypeConstraints/IWSAMsAndSRTPs/IWSAMsAndSRTPsTests.fs
+++ b/tests/FSharp.Compiler.ComponentTests/Conformance/Types/TypeConstraints/IWSAMsAndSRTPs/IWSAMsAndSRTPsTests.fs
@@ -287,6 +287,24 @@ let main _ =
             IL_000a:  ret
           }"""]
 
+    [<Fact>]
+    let ``SRTP get_Item works on strings`` () =
+        FSharp """
+let inline indexInto (slice: ^T when ^T: (member get_Item: int -> ^U)) i : ^U =
+    slice.get_Item i
+
+[<EntryPoint>]
+let main _ =
+    if indexInto "abcde" 2 <> 'c' then
+        failwith "Unexpected result"
+
+    0
+        """
+        |> asExe
+        |> withOptions ["--nowarn:77"]
+        |> compileAndRun
+        |> shouldSucceed
+
     [<Theory>]
     [<InlineData("let inline f_set_Item<'T when 'T : (member Item: int -> string with set) >(x: 'T) = (^T : (member Item: int -> string with set) (x, 3, \"a\"))")>]
     [<InlineData("let inline f_set_Item<'T when 'T : (member set_Item: int * string -> unit) >(x: 'T) = (^T : (member set_Item: int * string -> unit) (x, 3, \"a\"))")>]
@@ -699,6 +717,7 @@ let main _ =
         |> compileAndRun
         |> shouldSucceed
 
+
     [<InlineData(true)>]        // RealSig
     [<InlineData(false)>]       // Regular
     [<Theory>]
@@ -1955,4 +1974,3 @@ if resultInt <> 0 then failwith $"Expected 0 but got {resultInt}"
         |> asExe
         |> compileAndRun
         |> shouldSucceed
-