Bugfix :: Fix optimizer bug where field.Index included compiler generated static fields

src/Compiler/TypedTree/TypedTree.fs

@@ -4273,6 +4273,19 @@ type UnionCaseRef =
 
     override x.ToString() = x.CaseName
 
+let findLogicalFieldIndexOfRecordField (tcref:TyconRef) (id:string) =
+    let arr = tcref.AllFieldsArray
+
+    // We are skipping compiler generated fields such as "init@5" from index calculation
+    let rec go originalIdx skippedItems =
+        if originalIdx >= arr.Length then error(InternalError(sprintf "field %s not found in type %s" id tcref.LogicalName, tcref.Range))
+        else
+            let currentItem = arr[originalIdx]
+            if currentItem.LogicalName = id then (originalIdx-skippedItems)
+            else go (originalIdx + 1) (skippedItems + (if currentItem.IsCompilerGenerated && currentItem.IsStatic then 1 else 0))
+
+    go 0 0
+
 /// Represents a reference to a field in a record, class or struct
 [<NoEquality; NoComparison; StructuredFormatDisplay("{DebugText}")>]
 type RecdFieldRef = 
@@ -4316,11 +4329,8 @@ type RecdFieldRef =
 
     member x.Index =
         let (RecdFieldRef(tcref, id)) = x
-        try 
-            // REVIEW: this could be faster, e.g. by storing the index in the NameMap 
-            tcref.AllFieldsArray |> Array.findIndex (fun rfspec -> rfspec.LogicalName = id)  
-        with :? KeyNotFoundException -> 
-            error(InternalError(sprintf "field %s not found in type %s" id tcref.LogicalName, tcref.Range))
+        findLogicalFieldIndexOfRecordField tcref id
+
 
     [<DebuggerBrowsable(DebuggerBrowsableState.Never)>]
     member x.DebugText = x.ToString()

tests/FSharp.Compiler.ComponentTests/Conformance/BasicGrammarElements/StaticLet/RecordOptimizerRegression.fs

@@ -0,0 +1,14 @@
+module Test
+
+// https://github.com/dotnet/fsharp/issues/18165
+
+type FooBar =
+    { xyz : string }
+    static let staticLet = 1
+
+let doThing (foo : FooBar) =
+    let bar = { foo with xyz = foo.xyz }
+    let baz = { bar with xyz = bar.xyz }
+    printf "%O" baz
+
+doThing { xyz = "" }

tests/FSharp.Compiler.ComponentTests/Conformance/BasicGrammarElements/StaticLet/StaticLetInUnionsAndRecords.fs

@@ -95,6 +95,16 @@ init R 2
 1
 2"""
 
+[<Theory; Directory(__SOURCE_DIRECTORY__, Includes=[|"RecordOptimizerRegression.fs"|])>]
+let ``Static let - record optimizer regression`` compilation =
+    compilation
+    |> withOptimize
+    |> verifyCompileAndRun
+    |> shouldSucceed
+    |> withStdOutContains """{ xyz = "" }"""
+
+
+
 [<Theory; Directory(__SOURCE_DIRECTORY__, Includes=[|"LowercaseDuTest.fs"|])>]
 let ``Static let - lowercase DU`` compilation =
     compilation