Fix #19156

src/Compiler/Interactive/fsi.fs

@@ -2131,7 +2131,8 @@ type internal FsiDynamicCompiler
         if tcConfig.printAst then
             for input in declaredImpls do
                 fprintfn fsiConsoleOutput.Out "AST:"
-                fprintfn fsiConsoleOutput.Out "%+A" input
+                let layout = DebugPrint.implFileL input
+                fprintfn fsiConsoleOutput.Out "%s" (LayoutRender.showL layout)
 #endif
 
         diagnosticsLogger.AbortOnError(fsiConsoleOutput)

src/Compiler/TypedTree/TypedTreeOps.fs

@@ -11225,13 +11225,16 @@ let mkOptimizedRangeLoop (g: TcGlobals) (mBody, mFor, mIn, spInWhile) (rangeTy,
         | RangeCount.PossiblyOversize calc ->
             calc (fun count wouldOvf ->
                 buildLoop count (fun mkBody ->
+                    // mkBody creates expressions that may contain lambdas with unique stamps.
+                    // We need to copy the expression for the second branch to avoid duplicate type names.
+                    let mkBodyCopied idxVar loopVar = copyExpr g CloneAll (mkBody idxVar loopVar)
                     mkCond
                         DebugPointAtBinding.NoneAtInvisible
                         mIn
                         g.unit_ty
                         wouldOvf
                         (mkCountUpInclusive mkBody (tyOfExpr g count))
-                        (mkCompGenLetIn mIn (nameof count) (tyOfExpr g count) count (fun (_, count) -> mkCountUpExclusive mkBody count))))
+                        (mkCompGenLetIn mIn (nameof count) (tyOfExpr g count) count (fun (_, count) -> mkCountUpExclusive mkBodyCopied count))))
     )
 
 let mkDebugPoint m expr = 

tests/FSharp.Compiler.ComponentTests/EmittedIL/ComputedCollections/ForNInRangeArrays.fs

@@ -1,4 +1,4 @@
-let f0 f = [|for n in 1..10 do f (); yield n|]
+let f0 f = [|for n in 1..10 do f (); yield n|]
 let f00 f g = [|for n in 1..10 do f (); g (); yield n|]
 let f000 f = [|for n in 1..10 do f (); yield n; yield n + 1|]
 let f0000 () = [|for n in 1..10 do yield n|]
@@ -42,3 +42,8 @@ let f29 f g = [|let y = f () in let z = g () in for x in 1..2..10 -> x + y + z|]
 let f30 f g = [|let y = f () in g (); for x in 1..2..10 -> x + y|]
 let f31 f g = [|f (); g (); for x in 1..2..10 -> x|]
 let f32 f g = [|f (); let y = g () in for x in 1..2..10 -> x + y|]
+
+// https://github.com/dotnet/fsharp/issues/19156
+let f33 (start : int) (finish : int) f = [|for _ in start..finish -> id id ()|]
+let f34 (start : int64) (finish : int64) f = [|for _ in start..finish -> id id ()|]
+let f35 (start : uint64) (finish : uint64) f = [|for _ in start..finish -> id id ()|]

tests/FSharp.Compiler.ComponentTests/EmittedIL/ComputedCollections/ForNInRangeLists.fs

@@ -1,4 +1,4 @@
-let f0 f = [for n in 1..10 do f (); yield n]
+let f0 f = [for n in 1..10 do f (); yield n]
 let f00 f g = [|for n in 1..10 do f (); g (); yield n|]
 let f000 f = [for n in 1..10 do f (); yield n; yield n + 1]
 let f0000 () = [for n in 1..10 do yield n]
@@ -42,3 +42,8 @@ let f29 f g = [let y = f () in let z = g () in for x in 1..2..10 -> x + y + z]
 let f30 f g = [let y = f () in g (); for x in 1..2..10 -> x + y]
 let f31 f g = [f (); g (); for x in 1..2..10 -> x]
 let f32 f g = [f (); let y = g () in for x in 1..2..10 -> x + y]
+
+// https://github.com/dotnet/fsharp/issues/19156
+let f33 (start : int) (finish : int) f = [for _ in start..finish -> id id ()]
+let f34 (start : int64) (finish : int64) f = [for _ in start..finish -> id id ()]
+let f35 (start : uint64) (finish : uint64) f = [for _ in start..finish -> id id ()]

tests/FSharp.Compiler.ComponentTests/Language/RegressionTests.fs

@@ -19,3 +19,37 @@ type TestItemSeq =
         |> compile
         |> withErrorCodes [39]
         |> ignore
+
+    // https://github.com/dotnet/fsharp/issues/19156
+    [<Fact>]
+    let ``Generic list comprehension with nested lambda should not cause duplicate entry in type index table``() =
+        FSharp """
+module Test
+open System
+
+let f (start: DateTime) (stop: DateTime) (input: (DateTime * 'a) list) =
+    [
+        for i in start.Ticks .. stop.Ticks ->
+            input |> List.where (fun (k, v) -> true)
+    ]
+        """
+        |> compile
+        |> shouldSucceed
+        |> ignore
+
+    // https://github.com/dotnet/fsharp/issues/19156
+    [<Fact>]
+    let ``Generic array comprehension with nested lambda should not cause duplicate entry in type index table``() =
+        FSharp """
+module Test
+open System
+
+let f (start: DateTime) (stop: DateTime) (input: (DateTime * 'a) list) =
+    [|
+        for i in start.Ticks .. stop.Ticks ->
+            input |> List.where (fun (k, v) -> true)
+    |]
+        """
+        |> compile
+        |> shouldSucceed
+        |> ignore

tests/walkthroughs/DebugStepping/TheBigFileOfDebugStepping.fsx

@@ -190,6 +190,13 @@ let ListExpressionSteppingTest8 () =
             yield x 
         ]
 
+// Test case from https://github.com/dotnet/fsharp/issues/19156
+let ListExpressionSteppingTest9 () =
+    [
+        for i in DateTime.Now.Ticks .. DateTime.Now.Ticks + 1L ->
+            ['a', 1] |> List.where (fun (k, v) -> true)
+    ]
+
 let SeqExpressionSteppingTest1 () = 
     seq { yield 1 }
 
@@ -842,6 +849,7 @@ ListExpressionSteppingTest5()
 ListExpressionSteppingTest6()
 ListExpressionSteppingTest7()
 ListExpressionSteppingTest8()
+ListExpressionSteppingTest9 () |> ignore
 SeqExpressionSteppingTest1()|> Seq.length
 SeqExpressionSteppingTest2()|> Seq.length
 SeqExpressionSteppingTest3()|> Seq.length