method_parameter_count_changed.ron

SemverQuery(
    id: "method_parameter_count_changed",
    human_readable_name: "pub method parameter count changed",
    description: "Parameter count of a method has changed.",
    required_update: Major,
    lint_level: Deny,
    reference_link: Some("https://doc.rust-lang.org/cargo/reference/semver.html#fn-change-arity"),
    query: r#"
    {
        CrateDiff {
            baseline {
                item {
                    ... on ImplOwner {
                        visibility_limit @filter(op: "=", value: ["$public"]) @output

                        importable_path {
                            path @output @tag
                            public_api @filter(op: "=", value: ["$true"])
                        }

                        inherent_impl {
                            method {
                                method_visibility: visibility_limit @filter(op: "=", value: ["$public"]) @output
                                method_name: name @output @tag
                                public_api_eligible @filter(op: "=", value: ["$true"])

                                old_parameter_: parameter @fold @transform(op: "count") @output @tag(name: "parameters")

                                span_: span @optional {
                                    filename @output
                                    begin_line @output
                                }
                            }
                        }
                    }
                }
            }
            current {
                item {
                    ... on ImplOwner {
                        visibility_limit @filter(op: "=", value: ["$public"])
                        name @output

                        importable_path {
                            path @filter(op: "=", value: ["%path"])
                            public_api @filter(op: "=", value: ["$true"])
                        }

                        # We use "impl" instead of "inherent_impl" here because moving
                        # an inherently-implemented method to a trait is not necessarily
                        # a breaking change, but changing the parameter count is.
                        #
                        # Method names are not unique on an ImplOwner! It's perfectly valid to have
                        # both an inherent method `foo()` as well as a trait-provided method
                        # `<Self as Bar>::foo()` at the same time. Whenever possible, rustc
                        # attempts to "do the right thing" and dispatch to the correct one.
                        #
                        # Because of the above, this check has to be written as
                        # "there is no method with the correct name and number of arguments"
                        # rather than the (incorrect!) alternative
                        # "the named method does not have the correct number of arguments."
                        #
                        # The above by itself is still not enough: say if the method was removed,
                        # that still makes the "there is no method ..." statement true.
                        # So we add an additional clause demanding that a method by that name
                        # with appropriate visibility actually exists.
                        impl @fold @transform(op: "count") @filter(op: ">", value: ["$zero"]) {
                            method {
                                visibility_limit @filter(op: "one_of", value: ["$public_or_default"])
                                name @filter(op: "=", value: ["%method_name"])
                                public_api_eligible @filter(op: "=", value: ["$true"])
                            }
                        }
                        impl @fold @transform(op: "count") @filter(op: "=", value: ["$zero"]) {
                            method {
                                visibility_limit @filter(op: "one_of", value: ["$public_or_default"])
                                name @filter(op: "=", value: ["%method_name"])
                                public_api_eligible @filter(op: "=", value: ["$true"])

                                parameter @fold @transform(op: "count") @filter(op: "=", value: ["%parameters"])
                            }
                        }

                        # Get the non-matching methods by that name so we can report them
                        # in the lint error message.
                        impl @fold {
                            method {
                                visibility_limit @filter(op: "one_of", value: ["$public_or_default"])
                                name @filter(op: "=", value: ["%method_name"])
                                public_api_eligible @filter(op: "=", value: ["$true"])

                                current_parameter_: parameter @fold @transform(op: "count") @output

                                non_matching_span_: span @optional {
                                    filename @output
                                    begin_line @output
                                }
                            }
                        }
                    }
                }
            }
        }
    }"#,
    arguments: {
        "public": "public",
        "public_or_default": ["public", "default"],
        "true": true,
        "zero": 0,
    },
    error_message: "A publicly-visible method now takes a different number of parameters.",
    per_result_error_template: Some("{{join \"::\" path}}::{{method_name}} now takes {{unpack_if_singleton current_parameter_count}} parameters instead of {{old_parameter_count}}, in {{multiple_spans non_matching_span_filename non_matching_span_begin_line}}"),
)