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}}"),
)