IL: cache C# extension methods per CCU

docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

@@ -166,6 +166,7 @@
 
 ### Improved
 
+* IL: cache C# extension methods per CCU ([PR #20256](https://github.com/dotnet/fsharp/pull/20256))
 * Nullness warning FS3261 on dotted method or property access (e.g. `x.Member`) now underlines the receiver expression and includes the member name and (when known) the binding name in the message. ([Issue #19658](https://github.com/dotnet/fsharp/issues/19658), [PR #19814](https://github.com/dotnet/fsharp/pull/19814))
 * Direct delegate construction ([PR ##19993](https://github.com/dotnet/fsharp/pull/19993))
 

src/Compiler/Checking/NameResolution.fs

@@ -587,28 +587,16 @@ let GetTyconRefForExtensionMembers minfo (deref: Entity) amap m g =
         None
 
 /// Get the info for all the .NET-style extension members listed as static members in the type.
-let private GetCSharpStyleIndexedExtensionMembersForTyconRef (amap: Import.ImportMap) m  (tcrefOfStaticClass: TyconRef) =
+let private ComputeCSharpStyleExtensionMembers (amap: Import.ImportMap) m  (tcrefOfStaticClass: TyconRef) (importFailed: bool ref) =
     let g = amap.g
-
-    let isApplicable =
-        IsTyconRefUsedForCSharpStyleExtensionMembers g tcrefOfStaticClass ||
-
-        g.langVersion.SupportsFeature(LanguageFeature.CSharpExtensionAttributeNotRequired) &&
-        tcrefOfStaticClass.IsLocalRef &&
-        not tcrefOfStaticClass.IsTypeAbbrev
-
-    if not isApplicable then [] else
-
     let ty = generalizedTyconRef g tcrefOfStaticClass
-    let pri = NextExtensionMethodPriority()
 
     let methods =
         protectAssemblyExploration []
             (fun () -> GetImmediateIntrinsicMethInfosOfType (None, AccessorDomain.AccessibleFromSomeFSharpCode) g amap m ty)
 
     [ for minfo in methods do
         if IsMethInfoPlainCSharpStyleExtensionMember g m true minfo then
-            let ilExtMem = ILExtMem (tcrefOfStaticClass, minfo, pri)
             // The results are indexed by the TyconRef of the first 'this' argument, if any.
             // So we need to go and crack the type of the 'this' argument.
             //
@@ -620,9 +608,49 @@ let private GetCSharpStyleIndexedExtensionMembersForTyconRef (amap: Import.Impor
             // methods for tuple occur in C# code)
             let thisTyconRef = GetTyconRefForExtensionMembers minfo tcrefOfStaticClass.Deref amap m g
             match thisTyconRef with
-            | None -> ()
-            | Some (Some tcref) -> yield Choice1Of2(tcref, ilExtMem)
-            | Some None -> yield Choice2Of2 ilExtMem ]
+            | None -> importFailed.Value <- true
+            | Some thisTyconRefOpt -> yield (thisTyconRefOpt, minfo) ]
+
+let private GetCSharpStyleIndexedExtensionMembersForTyconRef (amap: Import.ImportMap) m (tcrefOfStaticClass: TyconRef) =
+    let g = amap.g
+
+    let isApplicable =
+        IsTyconRefUsedForCSharpStyleExtensionMembers g tcrefOfStaticClass ||
+
+        g.langVersion.SupportsFeature(LanguageFeature.CSharpExtensionAttributeNotRequired) &&
+        tcrefOfStaticClass.IsLocalRef &&
+        not tcrefOfStaticClass.IsTypeAbbrev
+
+    // Checked before touching the CCU or its cache, so a non-extension class costs nothing extra.
+    if not isApplicable then [] else
+
+    let shape =
+        // A local class is still gaining members while its own file is checked; only an imported one is
+        // immutable enough to share. The cache lives on the CCU, so it goes when the project does.
+        if tcrefOfStaticClass.IsLocalRef then
+            ComputeCSharpStyleExtensionMembers amap m tcrefOfStaticClass (ref false)
+        else
+            let cache = tcrefOfStaticClass.nlr.Ccu.Deref.CSharpStyleExtensionMembersCache
+            match cache.TryGetValue tcrefOfStaticClass.Stamp with
+            | true, shape -> shape :?> (TyconRef option * MethInfo) list
+            | _ ->
+                let importFailed = ref false
+                let shape = ComputeCSharpStyleExtensionMembers amap m tcrefOfStaticClass importFailed
+
+                if not importFailed.Value then
+                    cache.TryAdd(tcrefOfStaticClass.Stamp, (shape :> obj)) |> ignore
+
+                shape
+
+    if List.isEmpty shape then [] else
+
+    let pri = NextExtensionMethodPriority()
+
+    [ for thisTyconRefOpt, minfo in shape do
+        let ilExtMem = ILExtMem (tcrefOfStaticClass, minfo, pri)
+        match thisTyconRefOpt with
+        | Some tcref -> yield Choice1Of2(tcref, ilExtMem)
+        | None -> yield Choice2Of2 ilExtMem ]
 
 /// Query the declared properties of a type (including inherited properties)
 let IntrinsicPropInfosOfTypeInScope (infoReader: InfoReader) optFilter ad findFlag m ty =

src/Compiler/Checking/import.fs

@@ -875,6 +875,7 @@ let ImportILAssembly(amap: unit -> ImportMap, m, auxModuleLoader, xmlDocInfoLoad
           MemberSignatureEquality= (fun ty1 ty2 -> typeEquivAux EraseAll (amap()).g ty1 ty2)
           TryGetILModuleDef = (fun () -> Some ilModule)
           TypeForwarders = forwarders
+          CSharpStyleExtensionMembersCache = ConcurrentDictionary(1, 0)
           XmlDocumentationInfo =
               match xmlDocInfoLoader, fileName with
               | Some xmlDocInfoLoader, Some fileName -> xmlDocInfoLoader.TryLoad(fileName)

src/Compiler/Driver/CompilerImports.fs

@@ -5,6 +5,7 @@
 module internal FSharp.Compiler.CompilerImports
 
 open System
+open System.Collections.Concurrent
 open System.Collections.Generic
 open System.Diagnostics
 open System.IO
@@ -1532,6 +1533,7 @@ and [<Sealed>] TcImports
                         ImportProvidedType = (fun ty -> ImportProvidedType (tcImports.GetImportMap()) m ty)
                         TryGetILModuleDef = (fun () -> Some ilModule)
                         TypeForwarders = CcuTypeForwarderTable.Empty
+                        CSharpStyleExtensionMembersCache = ConcurrentDictionary(1, 0)
                         XmlDocumentationInfo =
                             match tcConfig.xmlDocInfoLoader with
                             | Some xmlDocInfoLoader -> xmlDocInfoLoader.TryLoad(fileName)
@@ -2156,6 +2158,7 @@ and [<Sealed>] TcImports
                         UsesFSharp20PlusQuotations = minfo.usesQuotations
                         MemberSignatureEquality = (fun ty1 ty2 -> typeEquivAux EraseAll (tcImports.GetTcGlobals()) ty1 ty2)
                         TypeForwarders = ImportILAssemblyTypeForwarders(tcImports.GetImportMap, m, ilModule.GetRawTypeForwarders())
+                        CSharpStyleExtensionMembersCache = ConcurrentDictionary(1, 0)
 #if !NO_TYPEPROVIDERS
                         XmlDocumentationInfo =
                             match tcConfig.xmlDocInfoLoader with

src/Compiler/Driver/ParseAndCheckInputs.fs

@@ -6,6 +6,7 @@ module internal FSharp.Compiler.ParseAndCheckInputs
 open System
 open System.IO
 open System.Threading
+open System.Collections.Concurrent
 open System.Collections.Generic
 
 open FSharp.Compiler.Parser
@@ -1098,6 +1099,7 @@ let GetInitialTcState (m, ccuName, tcConfig: TcConfig, tcGlobals, tcImports: TcI
             Contents = ccuContents
             MemberSignatureEquality = typeEquivAux EraseAll tcGlobals
             TypeForwarders = CcuTypeForwarderTable.Empty
+            CSharpStyleExtensionMembersCache = ConcurrentDictionary(1, 0)
             XmlDocumentationInfo = None
         }
 

src/Compiler/TypedTree/TypedTree.fs

@@ -5888,7 +5888,9 @@ type CcuData =
 
       /// The table of .NET CLI type forwarders for this assembly
       TypeForwarders: CcuTypeForwarderTable
-
+
+      CSharpStyleExtensionMembersCache: ConcurrentDictionary<Stamp, obj>
+
       XmlDocumentationInfo: XmlDocumentationInfo option }
 
     [<DebuggerBrowsable(DebuggerBrowsableState.Never)>]

src/Compiler/TypedTree/TypedTree.fsi

@@ -3,6 +3,7 @@ module internal rec FSharp.Compiler.TypedTree
 
 open System
 open System.Diagnostics
+open System.Collections.Concurrent
 open System.Collections.Generic
 open System.Collections.Immutable
 open Internal.Utilities.Collections
@@ -4228,6 +4229,10 @@ type CcuData =
 
         /// The table of .NET CLI type forwarders for this assembly
         TypeForwarders: CcuTypeForwarderTable
+
+        /// C#-style extension members of this assembly's static classes, keyed by static class stamp.
+        /// Typed as obj because MethInfo is declared after this file.
+        CSharpStyleExtensionMembersCache: ConcurrentDictionary<Stamp, obj>
         XmlDocumentationInfo: XmlDocumentationInfo option
     }