SemverQuery(
id: "trait_allows_fewer_const_generic_params",
human_readable_name: "trait now allows fewer const generic parameters",
description: "A trait now allows fewer 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 Trait {
visibility_limit @filter(op: "=", value: ["$public"])
name @output
importable_path {
path @tag @output
public_api @filter(op: "=", value: ["$true"])
}
generic_parameter @fold
@transform(op: "count")
@tag(name: "old_allowed_const_count")
@output(name: "old_allowed_const_count") {
... on GenericConstParameter {
old_allowed_consts: name @output
}
}
}
}
}
current {
item {
... on Trait {
visibility_limit @filter(op: "=", value: ["$public"]) @output
importable_path {
path @filter(op: "=", value: ["%path"])
public_api @filter(op: "=", value: ["$true"])
}
generic_parameter @fold
@transform(op: "count")
@filter(op: "<", value: ["%old_allowed_const_count"])
@output(name: "new_allowed_const_count") {
... on GenericConstParameter {
new_allowed_consts: name @output
}
}
span_: span @optional {
filename @output
begin_line @output
end_line @output
}
}
}
}
}
}"#,
arguments: {
"public": "public",
"true": true,
},
error_message: "A trait now allows fewer const generic parameters than it used to. Uses of this trait that supplied all previously-supported const generics will be broken.",
per_result_error_template: Some("trait {{name}} allows {{old_allowed_const_count}} -> {{new_allowed_const_count}} const generics in {{span_filename}}:{{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 trait bound with the old number
// of allowed const generics (including ones that provided default values),
// which will be too many generics for the new definition.
witness: None,
)