Dedup format specifier locations in computation expressions

src/Compiler/Checking/NameResolution.fs

@@ -2185,6 +2185,8 @@ type TcResultsSinkImpl(tcGlobals, ?sourceText: ISourceText) =
     let capturedOpenDeclarations = ResizeArray<OpenDeclaration>()
     let capturedFormatSpecifierLocations = ResizeArray<_>()
 
+    let capturedFormatSpecifierRanges = HashSet<range>()
+
     let capturedNameResolutionIdentifiers =
         HashSet<pos * string>
             { new IEqualityComparer<_> with
@@ -2289,7 +2291,8 @@ type TcResultsSinkImpl(tcGlobals, ?sourceText: ISourceText) =
                     capturedMethodGroupResolutions.Add(CapturedNameResolution(itemMethodGroup, [], occurrenceType, nenv, ad, m))
 
         member sink.NotifyFormatSpecifierLocation(m, numArgs) =
-            capturedFormatSpecifierLocations.Add((m, numArgs))
+            if capturedFormatSpecifierRanges.Add(m) then
+                capturedFormatSpecifierLocations.Add((m, numArgs))
 
         member sink.NotifyRelatedSymbolUse(m, item, kind) =
             if allowedRange m then

tests/FSharp.Compiler.Service.Tests/EditorTests.fs

@@ -541,6 +541,19 @@ let _ = debug "[LanguageService] Type checking fails for '%s' with content=%A an
                      (4, 82, 4, 84, 1);
                      (4, 108, 4, 110, 1)|]
 
+[<Fact>]
+let ``Format specifier locations not duplicated in CE`` () =
+    let input = "let _ = seq { sprintf \"%d\" 1 }"
+    let file = "/home/user/Test.fsx"
+    let _parseResult, typeCheckResults = parseAndCheckScript(file, input)
+
+    let locations = typeCheckResults.GetFormatSpecifierLocationsAndArity()
+    let percentD =
+        locations
+        |> Array.filter (fun (r, _) -> r.StartColumn = 23)
+
+    Assert.Equal(1, percentD.Length)
+
 #if ASSUME_PREVIEW_FSHARP_CORE
 [<Fact>]
 let ``Printf specifiers for regular and verbatim interpolated strings`` () =