public static void SetParameterFcsType()

in ReSharper.FSharp/src/FSharp/FSharp.Psi/src/Util/FSharpPatternUtil.cs [170:221]
45 lines of code
10 McCabe index (conditional complexity)

    public static void SetParameterFcsType(this IList<IFSharpPattern> parameterPatternGroups,
      [NotNull] IFSharpParameterOwnerDeclaration paramOwnerDecl, FSharpParameterIndex index, FSharpType fcsType)
    {
      var typeAnnotationUtil = paramOwnerDecl.GetFSharpTypeAnnotationUtil();

      if (parameterPatternGroups.GetParameterDeclaration(index) is IReferencePat refPat)
      {
        var declPat = refPat.TryGetContainingParameterDeclarationPattern();
        typeAnnotationUtil.SetPatternFcsType(declPat, fcsType);
        return;
      }

      if (parameterPatternGroups.ElementAtOrDefault(index.GroupIndex) is not { } groupPattern)
        return;

      if (index.ParameterIndex is { } parameterIndex)
      {
        if (groupPattern.IgnoreInnerParens() is ITypedPat { TypeUsage: ITupleTypeUsage tupleTypeUsage })
        {
          if (tupleTypeUsage.Items.ElementAtOrDefault(parameterIndex) is { } paramTypeUsage)
            typeAnnotationUtil.ReplaceWithFcsType(paramTypeUsage, fcsType);
        }
        else
        {
          // todo: union case
          if (paramOwnerDecl.GetFcsSymbol() is not FSharpMemberOrFunctionOrValue mfv)
            return;

          var fcsParamGroup = mfv.CurriedParameterGroups.ElementAtOrDefault(index.GroupIndex);
          if (fcsParamGroup == null)
            return;

          var fcsGroupParameterCount = GetFcsGroupParameterCount(fcsParamGroup);
          if (fcsGroupParameterCount == 1)
          {
            typeAnnotationUtil.SetPatternFcsType(groupPattern, fcsType);
            return;
          }

          var factory = paramOwnerDecl.CreateElementFactory();
          var tupleTypeString = Enumerable.Repeat("_", fcsGroupParameterCount).Join(" * ");
          var newTypeUsage = factory.CreateTypeUsage(tupleTypeString, TypeUsageContext.TopLevel);
          var typeUsage = (ITupleTypeUsage)typeAnnotationUtil.SetPatternTypeUsage(groupPattern, newTypeUsage).TypeUsage;
          if (typeUsage.Items.ElementAtOrDefault(parameterIndex) is { } paramTypeUsage)
            typeAnnotationUtil.ReplaceWithFcsType(paramTypeUsage, fcsType);
        }
      }
      else
      {
        typeAnnotationUtil.SetPatternFcsType(groupPattern, fcsType);
      }
    }