codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/integration/ValidationGenerator.java [240:263]:
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                                writer.write("invalidParams.AddNested(fmt.Sprintf(\"[%q]\", key), "
                                        + "err.(smithy.InvalidParamsError))");
                            });
                        });
                        break;

                    case UNION:
                        UnionShape unionShape = shape.asUnionShape().get();
                        Symbol unionSymbol = symbolProvider.toSymbol(unionShape);

                        Set<MemberShape> memberShapes = unionShape.getAllMembers().values().stream()
                                .filter(memberShape ->
                                        shapesWithHelpers.contains(model.expectShape(memberShape.getTarget()).getId()))
                                .collect(Collectors.toCollection(TreeSet::new));

                        if (memberShapes.size() > 0) {
                            writer.openBlock("switch uv := v.(type) {", "}", () -> {
                                // Use a TreeSet to sort the members.
                                for (MemberShape unionMember : memberShapes) {
                                    Shape target = model.expectShape(unionMember.getTarget());
                                    Symbol memberSymbol = SymbolUtils.createValueSymbolBuilder(
                                            symbolProvider.toMemberName(unionMember),
                                            unionSymbol.getNamespace()
                                    ).build();
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codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/server/ServerValidationgenerator.java [191:214]:
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                                writer.write("invalidParams.AddNested(fmt.Sprintf(\"[%q]\", key), "
                                        + "err.(smithy.InvalidParamsError))");
                            });
                        });
                        break;

                    case UNION:
                        UnionShape unionShape = shape.asUnionShape().get();
                        Symbol unionSymbol = symbolProvider.toSymbol(unionShape);

                        Set<MemberShape> memberShapes = unionShape.getAllMembers().values().stream()
                                .filter(memberShape ->
                                        shapesWithHelpers.contains(model.expectShape(memberShape.getTarget()).getId()))
                                .collect(Collectors.toCollection(TreeSet::new));

                        if (memberShapes.size() > 0) {
                            writer.openBlock("switch uv := v.(type) {", "}", () -> {
                                // Use a TreeSet to sort the members.
                                for (MemberShape unionMember : memberShapes) {
                                    Shape target = model.expectShape(unionMember.getTarget());
                                    Symbol memberSymbol = SymbolUtils.createValueSymbolBuilder(
                                            symbolProvider.toMemberName(unionMember),
                                            unionSymbol.getNamespace()
                                    ).build();
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