From cd07a7d1cde42d7cf1ed52d462c2a443aa96982d Mon Sep 17 00:00:00 2001
From: Martin521 <29605222+Martin521@users.noreply.github.com>
Date: Wed, 2 Apr 2025 10:57:10 +0000
Subject: [PATCH 1/2] fix for 18433

---
 src/Compiler/SyntaxTree/XmlDoc.fs                |  3 ++-
 .../Language/XmlComments.fs                      | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/Compiler/SyntaxTree/XmlDoc.fs b/src/Compiler/SyntaxTree/XmlDoc.fs
index a366a69a8a6..d4c4cada576 100644
--- a/src/Compiler/SyntaxTree/XmlDoc.fs
+++ b/src/Compiler/SyntaxTree/XmlDoc.fs
@@ -139,7 +139,8 @@ type XmlDocCollector() =
             let xmlDocBlock =
                 struct (savedLines.Count - currentGrabPointCommentsCount, savedLines.Count - 1, false)
 
-            savedGrabPoints.Add(pos, xmlDocBlock)
+            // silently override duplicate grab points (which happen only when preceded by nonsensical line directives)
+            savedGrabPoints[pos] <- xmlDocBlock
             currentGrabPointCommentsCount <- 0
             delayedGrabPoint <- ValueNone
 
diff --git a/tests/FSharp.Compiler.ComponentTests/Language/XmlComments.fs b/tests/FSharp.Compiler.ComponentTests/Language/XmlComments.fs
index eed0e37e4db..47aee9362b7 100644
--- a/tests/FSharp.Compiler.ComponentTests/Language/XmlComments.fs
+++ b/tests/FSharp.Compiler.ComponentTests/Language/XmlComments.fs
@@ -242,3 +242,19 @@ module M =
          |> withXmlCommentChecking
          |> compile
          |> withDiagnostics [ ]
+
+    // regression test for #18433
+    [<Fact>]
+    let OverrideXmlCommentsWithSameRange () =
+        Fs"""
+        module A
+        # 1
+        /// A is int
+        type A = {a: int}
+        # 1
+        /// B is int
+        type B = {b: int}
+        """
+        |> withXmlCommentChecking
+        |> compile
+        |> shouldSucceed
\ No newline at end of file

From e6ced7a0ca8f45bb87ecdb9c2ca060b074b2bb28 Mon Sep 17 00:00:00 2001
From: Martin521 <29605222+Martin521@users.noreply.github.com>
Date: Wed, 2 Apr 2025 11:13:30 +0000
Subject: [PATCH 2/2] release note for #18436

---
 docs/release-notes/.FSharp.Compiler.Service/9.0.300.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docs/release-notes/.FSharp.Compiler.Service/9.0.300.md b/docs/release-notes/.FSharp.Compiler.Service/9.0.300.md
index 86672567838..8893e4d237d 100644
--- a/docs/release-notes/.FSharp.Compiler.Service/9.0.300.md
+++ b/docs/release-notes/.FSharp.Compiler.Service/9.0.300.md
@@ -21,6 +21,7 @@
 * Fix MethodDefNotFound when compiling code invoking delegate with option parameter ([Issue #5171](https://github.com/dotnet/fsharp/issues/5171), [PR #18385](https://github.com/dotnet/fsharp/pull/18385))
 * Fix #r nuget ..." downloads unneeded packages ([Issue #18231](https://github.com/dotnet/fsharp/issues/18231), [PR #18393](https://github.com/dotnet/fsharp/pull/18393))
 * Reenable β-reduction and subsequent reoptimization of immediately-invoked F#-defined generic delegates. ([PR #18401](https://github.com/dotnet/fsharp/pull/18401))
+* Fixed [#18433](https://github.com/dotnet/fsharp/issues/18433), a rare case of an internal error in xml comment processing. ([PR #18436](https://github.com/dotnet/fsharp/pull/18436))
 
 ### Added
 * Added missing type constraints in FCS. ([PR #18241](https://github.com/dotnet/fsharp/pull/18241))