Use culture-independent IndexOf in interpolated string parsing

docs/release-notes/.FSharp.Core/10.0.300.md

@@ -6,6 +6,7 @@
 * Fix tuple/multi-value projections in queries to use Queryable.Select instead of Enumerable.Select when the source is IQueryable, preserving query composition and enabling async operations like ToListAsync() in Entity Framework Core. ([Issue #3782](https://github.com/dotnet/fsharp/issues/3782), [Issue #15133](https://github.com/dotnet/fsharp/issues/15133))
 * Fix EvaluateQuotation to handle Sequential expressions, void method calls (unit return), and other patterns that were previously throwing NotSupportedException. Also properly handles unit-returning expressions by using Action delegates instead of Func delegates. ([Issue #19099](https://github.com/dotnet/fsharp/issues/19099))
 * Fix query conditionals without else branch (if-then only) that were causing type mismatch errors. Now properly extracts element type from IQueryable for creating empty sequences. ([Issue #3445](https://github.com/dotnet/fsharp/issues/3445))
+* Ensure culture-independent parsing of .NET-style interpolated string holes. ([Issue #19367](https://github.com/dotnet/fsharp/issues/19367), [PR #19370](https://github.com/dotnet/fsharp/pull/19370))
 
 ### Added
 

src/FSharp.Core/printf.fs

@@ -209,7 +209,7 @@ module internal PrintfImpl =
         let parseInterpolatedHoleDotNetFormat typeChar (s: string) (i: byref<int>) =
             if typeChar = 'P' then 
                 if i < s.Length && s.[i] = '(' then  
-                     let i2 = s.IndexOf(")", i)
+                     let i2 = s.IndexOf(')', i)
                      if i2 = -1 then 
                          ValueNone
                      else 

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

@@ -181,4 +181,26 @@ printfn "%%s" (System.Globalization.CultureInfo "en-US" |> x.ToString)
         """
         |> compileExeAndRun
         |> shouldSucceed
-        |> withStdOutContains "abcde"
+        |> withStdOutContains "abcde"
+
+    // See https://github.com/dotnet/fsharp/issues/19367.
+    [<CulturedFact([|"th"|])>]
+    let ``Hole without specifier parsed correctly when culture set to Thai`` () =
+        Fsx
+            """
+            let s = $"{3}"
+            if s <> "3" then
+                failwith $"Expected \"3\" but got \"%s{s}\"."
+            """
+        |> compileExeAndRun
+        |> shouldSucceed
+
+    // See https://github.com/dotnet/fsharp/issues/19367.
+    [<CulturedFact([|"th"|])>]
+    let ``Explicit %P does not cause exception when culture set to Thai`` () =
+        Fsx
+            """
+            let s = $"%P({3})"
+            """
+        |> compileExeAndRun
+        |> shouldSucceed