New lint: disallowed_trait_usage

CHANGELOG.md

@@ -6540,6 +6540,7 @@ Released 2018-09-13
 [`disallowed_methods`]: https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_methods
 [`disallowed_names`]: https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_names
 [`disallowed_script_idents`]: https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_script_idents
+[`disallowed_trait_usage`]: https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_trait_usage
 [`disallowed_type`]: https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_type
 [`disallowed_types`]: https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_types
 [`diverging_sub_expression`]: https://rust-lang.github.io/rust-clippy/master/index.html#diverging_sub_expression
@@ -7363,6 +7364,7 @@ Released 2018-09-13
 [`disallowed-macros`]: https://doc.rust-lang.org/clippy/lint_configuration.html#disallowed-macros
 [`disallowed-methods`]: https://doc.rust-lang.org/clippy/lint_configuration.html#disallowed-methods
 [`disallowed-names`]: https://doc.rust-lang.org/clippy/lint_configuration.html#disallowed-names
+[`disallowed-trait-usage`]: https://doc.rust-lang.org/clippy/lint_configuration.html#disallowed-trait-usage
 [`disallowed-types`]: https://doc.rust-lang.org/clippy/lint_configuration.html#disallowed-types
 [`doc-valid-idents`]: https://doc.rust-lang.org/clippy/lint_configuration.html#doc-valid-idents
 [`enable-raw-pointer-heuristic-for-send`]: https://doc.rust-lang.org/clippy/lint_configuration.html#enable-raw-pointer-heuristic-for-send

book/src/lint_configuration.md

@@ -585,6 +585,33 @@ default configuration of Clippy. By default, any configuration will replace the
 * [`disallowed_names`](https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_names)
 
 
+## `disallowed-trait-usage`
+The list of disallowed trait usages. Each entry forbids using a type via a specific
+trait interface.
+
+**Fields:**
+- `type` (optional): the fully qualified path to a concrete type (e.g. `"i32"`, `"std::path::PathBuf"`)
+- `implements` (optional): the fully qualified path to a trait; matches any type implementing it
+- `trait` (required): the fully qualified path to the disallowed trait (e.g. `"std::fmt::Debug"`)
+- `reason` (optional): explanation why this trait usage is disallowed
+
+Exactly one of `type` or `implements` must be specified.
+
+### Example
+```toml
+disallowed-trait-usage = [
+    { type = "std::path::PathBuf", trait = "std::fmt::Debug", reason = "Use path.display() instead" },
+    { implements = "std::error::Error", trait = "std::fmt::Debug", reason = "Use Display instead" },
+]
+```
+
+**Default Value:** `[]`
+
+---
+**Affected lints:**
+* [`disallowed_trait_usage`](https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_trait_usage)
+
+
 ## `disallowed-types`
 The list of disallowed types, written as fully qualified paths.
 

clippy_config/src/conf.rs

@@ -628,6 +628,26 @@ define_Conf! {
     /// default configuration of Clippy. By default, any configuration will replace the default value.
     #[lints(disallowed_names)]
     disallowed_names: Vec<String> = DEFAULT_DISALLOWED_NAMES.iter().map(ToString::to_string).collect(),
+    /// The list of disallowed trait usages. Each entry forbids using a type via a specific
+    /// trait interface.
+    ///
+    /// **Fields:**
+    /// - `type` (optional): the fully qualified path to a concrete type (e.g. `"i32"`, `"std::path::PathBuf"`)
+    /// - `implements` (optional): the fully qualified path to a trait; matches any type implementing it
+    /// - `trait` (required): the fully qualified path to the disallowed trait (e.g. `"std::fmt::Debug"`)
+    /// - `reason` (optional): explanation why this trait usage is disallowed
+    ///
+    /// Exactly one of `type` or `implements` must be specified.
+    ///
+    /// ### Example
+    /// ```toml
+    /// disallowed-trait-usage = [
+    ///     { type = "std::path::PathBuf", trait = "std::fmt::Debug", reason = "Use path.display() instead" },
+    ///     { implements = "std::error::Error", trait = "std::fmt::Debug", reason = "Use Display instead" },
+    /// ]
+    /// ```
+    #[lints(disallowed_trait_usage)]
+    disallowed_trait_usage: Vec<crate::types::DisallowedTraitUsage> = Vec::new(),
     /// The list of disallowed types, written as fully qualified paths.
     ///
     /// **Fields:**

clippy_config/src/types.rs

@@ -671,6 +671,28 @@ impl Serialize for SourceItemOrderingWithinModuleItemGroupings {
     }
 }
 
+/// An entry in the `disallowed-trait-usage` configuration.
+///
+/// Forbids using a type via a specific trait interface. The type can be specified
+/// either as a concrete type (`type`) or as a trait bound (`implements`), but not both.
+#[derive(Debug, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct DisallowedTraitUsage {
+    /// The fully qualified path to a concrete type (e.g. `"i32"`, `"std::path::PathBuf"`).
+    /// Mutually exclusive with `implements`.
+    #[serde(rename = "type")]
+    pub type_path: Option<String>,
+    /// The fully qualified path to a trait (e.g. `"std::error::Error"`).
+    /// When set, the rule applies to any type that implements this trait.
+    /// Mutually exclusive with `type`.
+    pub implements: Option<String>,
+    /// The fully qualified path to the trait being disallowed (e.g. `"std::fmt::Debug"`).
+    #[serde(rename = "trait")]
+    pub trait_path: String,
+    /// Optional reason explaining why this usage is disallowed.
+    pub reason: Option<String>,
+}
+
 // these impls are never actually called but are used by the various config options that default to
 // empty lists
 macro_rules! unimplemented_serialize {
@@ -689,6 +711,7 @@ macro_rules! unimplemented_serialize {
 }
 
 unimplemented_serialize! {
+    DisallowedTraitUsage,
     Rename,
     MacroMatcher,
 }

clippy_lints/src/declared_lints.rs

@@ -110,6 +110,7 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::disallowed_methods::DISALLOWED_METHODS_INFO,
     crate::disallowed_names::DISALLOWED_NAMES_INFO,
     crate::disallowed_script_idents::DISALLOWED_SCRIPT_IDENTS_INFO,
+    crate::disallowed_trait_usage::DISALLOWED_TRAIT_USAGE_INFO,
     crate::disallowed_types::DISALLOWED_TYPES_INFO,
     crate::doc::DOC_BROKEN_LINK_INFO,
     crate::doc::DOC_COMMENT_DOUBLE_SPACE_LINEBREAKS_INFO,