Fix #16398 - The dotnet framework has a limit of ~64K methods in a single class.

docs/release-notes/.FSharp.Compiler.Service/8.0.200.md

@@ -2,6 +2,7 @@
 
 * Miscellaneous fixes to parentheses analysis. ([PR #16262](https://github.com/dotnet/fsharp/pull/16262), [PR #16391](https://github.com/dotnet/fsharp/pull/16391), [PR #16370](https://github.com/dotnet/fsharp/pull/16370), [PR #16395](https://github.com/dotnet/fsharp/pull/16395))
 * Correctly handle assembly imports with public key token of 0 length. ([Issue #16359](https://github.com/dotnet/fsharp/issues/16359), [PR #16363](https://github.com/dotnet/fsharp/pull/16363))
+* Fix #16398 - The dotnet framework has a limit of ~64K methods in a single class.  Introduce a compile-time error if any class has over approx 64K methods in generated IL
 
 ### Added
 * Raise a new error when interfaces with auto properties are implemented on constructor-less types. ([PR #16352](https://github.com/dotnet/fsharp/pull/16352))

src/Compiler/AbstractIL/ilwrite.fs

@@ -50,6 +50,13 @@ let emitBytesViaBuffer f = use bb = ByteBuffer.Create EmitBytesViaBufferCapacity
 /// Alignment and padding
 let align alignment n = ((n + alignment - 1) / alignment) * alignment
 
+
+/// Maximum number of methods in a dotnet type
+/// This differs from the spec and file formats slightly which suggests 0xfffe is the maximum
+/// this value was identified empirically.
+[<Literal>]
+let maximumMethodsPerDotNetType = 0xfff0
+
 //---------------------------------------------------------------------
 // Concrete token representations etc. used in PE files
 //---------------------------------------------------------------------
@@ -672,8 +679,14 @@ let GetTypeNameAsElemPair cenv n =
 //=====================================================================
 
 let rec GenTypeDefPass1 enc cenv (tdef: ILTypeDef) =
-  ignore (cenv.typeDefs.AddUniqueEntry "type index" (fun (TdKey (_, n)) -> n) (TdKey (enc, tdef.Name)))
-  GenTypeDefsPass1 (enc@[tdef.Name]) cenv (tdef.NestedTypes.AsList())
+    ignore (cenv.typeDefs.AddUniqueEntry "type index" (fun (TdKey (_, n)) -> n) (TdKey (enc, tdef.Name)))
+
+    // Verify that the typedef contains fewer than maximumMethodsPerDotNetType
+    let count = tdef.Methods.AsArray().Length
+    if count > maximumMethodsPerDotNetType then
+        errorR(Error(FSComp.SR.tooManyMethodsInDotNetTypeWritingAssembly (tdef.Name, count, maximumMethodsPerDotNetType), rangeStartup))
+
+    GenTypeDefsPass1 (enc@[tdef.Name]) cenv (tdef.NestedTypes.AsList())
 
 and GenTypeDefsPass1 enc cenv tdefs = List.iter (GenTypeDefPass1 enc cenv) tdefs
 
@@ -682,7 +695,8 @@ and GenTypeDefsPass1 enc cenv tdefs = List.iter (GenTypeDefPass1 enc cenv) tdefs
 //=====================================================================
 
 let rec GetIdxForTypeDef cenv key =
-    try cenv.typeDefs.GetTableEntry key
+    try
+        cenv.typeDefs.GetTableEntry key
     with
       :? KeyNotFoundException ->
         let (TdKey (enc, n) ) = key

src/Compiler/FSComp.txt

@@ -1738,4 +1738,5 @@ featureReuseSameFieldsInStructUnions,"Share underlying fields in a [<Struct>] di
 3860,chkStaticMembersOnObjectExpressions,"Object expressions cannot implement interfaces with static abstract members or declare static members."
 3861,chkTailCallAttrOnNonRec,"The TailCall attribute should only be applied to recursive functions."
 3862,parsStaticMemberImcompleteSyntax,"Incomplete declaration of a static construct. Use 'static let','static do','static member' or 'static val' for declaration."
-3863,parsExpectingField,"Expecting record field"
+3863,parsExpectingField,"Expecting record field"
+3864,tooManyMethodsInDotNetTypeWritingAssembly,"The type '%s' has too many methods. Found: '%d', maximum: '%d'"

tests/FSharp.Compiler.ComponentTests/EmittedIL/VeryLargeClasses.fs

@@ -0,0 +1,50 @@
+namespace EmittedIL
+
+open Microsoft.FSharp.Core
+open Xunit
+open FSharp.Test.Compiler
+
+module VeryLargeClasses =
+
+    let classWithManyMethods n =
+        let methods =
+            let mutable source = ""
+            for i = 0 to n - 1 do
+                source <- source + $"""
+                static member Method%05x{i}() = () """
+            source
+
+        FSharp
+            $"""
+            namespace VeryLargeClassesTestcases
+
+            type Type1 ={methods}
+                """
+
+    [<Fact>]
+    let ``More than 64K Methods -- should fail`` () =
+        classWithManyMethods (1024 * 64 + 1)
+        |> compile
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 3864, Line 1, Col 1, Line 1, Col 1, "The type 'VeryLargeClassesTestcases.Type1' has too many methods. Found: '65537', maximum: '65520'")
+        ]
+
+    [<Fact>]
+    let ``Exactly (0xfff0) Methods -- should succeed`` () =
+        FSharp
+            """
+module MyMain
+open System
+open System.Reflection
+do printfn $"location: {typeof<VeryLargeClassesTestcases.Type1>.Assembly.Location}"
+let asm = Assembly.LoadFrom(typeof<VeryLargeClassesTestcases.Type1>.Assembly.Location)
+printfn $"asm: {asm}"
+let types = asm.GetTypes()
+printfn "length: {types.Length}"
+"""
+        |> withReferences [ classWithManyMethods 0xfff0 |> asLibrary ]
+        |> asExe
+        |> compileAndRun
+        |> shouldSucceed
+

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

@@ -124,6 +124,7 @@
     <Compile Include="Conformance\UnitsOfMeasure\Parsing.fs" />
     <Compile Include="Conformance\UnitsOfMeasure\TypeChecker.fs" />
     <Compile Include="EmittedIL\CompilerGeneratedAttributeOnAccessors.fs" />
+    <Compile Include="EmittedIL\VeryLargeClasses.fs" />
     <Compile Include="EmittedIL\EmptyArray.fs" />
     <Compile Include="EmittedIL\Enums.fs" />
     <Compile Include="EmittedIL\Literals.fs" />

tests/FSharp.Test.Utilities/CompilerAssert.fs

@@ -386,7 +386,7 @@ module rec CompilerAssertHelpers =
         let name =
             match nameOpt with
             | Some name -> name
-            | _ -> tryCreateTemporaryFileName()
+            | _ -> tryCreateTemporaryFileNameInDirectory(outputDirectory)
 
         let outputFilePath = Path.ChangeExtension (Path.Combine(outputDirectory.FullName, name), if isExe then ".exe" else ".dll")
         disposals.Add(disposeFile outputFilePath)

tests/FSharp.Test.Utilities/TestFramework.fs

@@ -28,12 +28,11 @@ let tryCreateTemporaryFileName () =
     filePath
 
 // Create a temporaryFileName -- newGuid is random --- there is no point validating the file alread exists because: threading and Path.ChangeExtension() is commonly used after this API
-let tryCreateTemporaryFileNameInDirectory (directory) =
+let tryCreateTemporaryFileNameInDirectory (directory: DirectoryInfo) =
     let fileName = ("Temp-" + Guid.NewGuid().ToString() + ".tmp").Replace('-', '_')
-    let filePath = Path.Combine(directory, fileName)
+    let filePath = Path.Combine(directory.FullName, fileName)
     filePath
 
-
 [<RequireQualifiedAccess>]
 module Commands =
 

tests/service/ScriptOptionsTests.fs

@@ -50,9 +50,9 @@ let ``can generate options for different frameworks regardless of execution envi
 [<TestCase([| "--targetprofile:netstandard" |])>]
 [<Test>]
 let ``can resolve nuget packages to right target framework for different frameworks regardless of execution environment``(flags) =
-    let path = Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location)
+    let path = DirectoryInfo(Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location))
     let file = tryCreateTemporaryFileNameInDirectory(path) + ".fsx"
-    let scriptFullPath = Path.Combine(path, file)
+    let scriptFullPath = Path.Combine(path.FullName, file)
     let scriptSource = """
 #r "nuget: FSharp.Data, 3.3.3"
 open System