Fix UoM ToString codegen with checknulls

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

@@ -12,6 +12,7 @@
 * Improve let-rec codegen: reorder bindings to allocate lambda closures before non-lambda values that reference them. ([PR #19339](https://github.com/dotnet/fsharp/pull/19339))
 * Fix `YieldFromFinal`/`ReturnFromFinal` being incorrectly called in non-tail positions (`for`, `use`, `use!`, `try/with` handler). ([Issue #19402](https://github.com/dotnet/fsharp/issues/19402), [PR #19403](https://github.com/dotnet/fsharp/pull/19403))
 * Fixed how the source ranges of warn directives are reported (as trivia) in the parser output (by not reporting leading spaces). ([Issue #19405](https://github.com/dotnet/fsharp/issues/19405), [PR #19408]((https://github.com/dotnet/fsharp/pull/19408)))
+* Fix UoM value type `ToString()` returning garbage values when `--checknulls+` is enabled, caused by double address-taking in codegen. ([Issue #19435](https://github.com/dotnet/fsharp/issues/19435), [PR #19440](https://github.com/dotnet/fsharp/pull/19440))
 
 ### Added
 

src/Compiler/Checking/MethodCalls.fs

@@ -1231,11 +1231,17 @@ let rec BuildMethodCall tcVal g amap isMutable m isProp minfo valUseFlags minst
             let vExpr, vExprTy = tcVal vref valUseFlags (minfo.DeclaringTypeInst @ minst) m
             BuildFSharpMethodApp g m vref vExpr vExprTy allArgs
 
-        | MethInfoWithModifiedReturnType(mi,retTy) ->
-            let expr, exprTy = BuildMethodCall tcVal g amap isMutable m isProp mi valUseFlags minst objArgs args staticTyOpt
-            let expr = mkCoerceExpr(expr, retTy, m, exprTy)
+        | MethInfoWithModifiedReturnType(ILMeth(_, ilMethInfo, _), retTy) ->
+            // Build the inner call directly, without re-invoking TakeObjAddrForMethodCall.
+            let expr, exprTy =
+                BuildILMethInfoCall g amap m isProp ilMethInfo valUseFlags minst direct allArgs
+
+            let expr = mkCoerceExpr (expr, retTy, m, exprTy)
             expr, retTy
 
+        | MethInfoWithModifiedReturnType _ ->
+            failwith "MethInfoWithModifiedReturnType: unexpected inner method kind"
+
         // Build a 'call' to a struct default constructor 
         | DefaultStructCtor (g, ty) -> 
             if g.langFeatureNullness && g.checkNullness then

tests/FSharp.Compiler.ComponentTests/Language/Nullness/NullableReferenceTypesTests.fs

@@ -734,6 +734,29 @@ let processAlias (x:mykgalias) =
     |> typeCheckWithStrictNullness
     |> shouldSucceed
 
+// https://github.com/dotnet/fsharp/issues/19435
+[<Theory>]
+[<InlineData("42<mykg>", "42")>]
+[<InlineData("42.0<mykg>", "42")>]
+[<InlineData("42M<mykg>", "42")>]
+let ``ToString on value type with UoM does not produce garbage at runtime`` (valueExpr: string, expected: string) =
+    FSharp $"""
+module MyProgram
+
+[<Measure>]
+type mykg
+
+[<EntryPoint>]
+let main _ =
+    let x = {valueExpr}
+    System.Console.Write(x.ToString())
+    0
+    """
+    |> withCheckNulls
+    |> compileExeAndRun
+    |> shouldSucceed
+    |> withStdOutContains expected
+
 [<Fact>]
 let ``Printing a nullable string should pass`` () = 
     FSharp """module MyLibrary