SemverQuery(
id: "method_requires_different_const_generic_params",
human_readable_name: "method now requires a different number of const generic parameters",
// Currently, const generics in functions and methods cannot have defaults set.
// This is why we have only one lint ("requires different number") instead of
// two separate lints ("requires" / "allows") like for structs/traits etc.
description: "A method now requires a different number of const generic parameters than before.",
required_update: Major,
lint_level: Deny,
reference_link: Some("https://doc.rust-lang.org/reference/items/generics.html#const-generics"),
query: r#"
{
CrateDiff {
baseline {
item {
... on ImplOwner {
visibility_limit @filter(op: "=", value: ["$public"])
importable_path {
path @tag @output
public_api @filter(op: "=", value: ["$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"])
generic_parameter @fold
@transform(op: "count")
@tag(name: "old_required_const_count")
@output(name: "old_required_const_count") {
... on GenericConstParameter {
old_required_consts: name @output
}
}
span_: span @optional {
filename @output
begin_line @output
end_line @output
}
}
}
}
}
}
current {
item {
... on ImplOwner {
visibility_limit @filter(op: "=", value: ["$public"]) @output
name @output
importable_path {
path @filter(op: "=", value: ["%path"])
public_api @filter(op: "=", value: ["$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 number of const generics 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 const generics"
# 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"])
generic_parameter @fold
@transform(op: "count")
@filter(op: "=", value: ["%old_required_const_count"]) {
... on GenericConstParameter {
name
}
}
}
}
# 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"])
generic_parameter @fold
@transform(op: "count")
@output(name: "new_required_const_count") {
... on GenericConstParameter {
new_required_consts: name @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 method now requires a different number of const generic parameters than it used to. Uses of this method that supplied the previous number of const generics will be broken.",
per_result_error_template: Some("{{join \"::\" path}}::{{method_name}} takes {{unpack_if_singleton new_required_const_count}} const generics instead of {{old_required_const_count}}, in {{multiple_spans non_matching_span_filename non_matching_span_begin_line}}"),
// TODO: see https://github.com/obi1kenobi/cargo-semver-checks/blob/main/CONTRIBUTING.md#adding-a-witness
// for information about this field.
//
// The witness would be a invocation with the old number
// of const generics, which is insufficient for the new definition.
witness: None,
)