New lint: Inherent method #[must_use] added

src/lints/inherent_method_must_use_added.ron

@@ -0,0 +1,80 @@
+SemverQuery(
+    id: "inherent_method_must_use_added",
+    human_readable_name: "inherent method #[must_use] added",
+    description: "An inherent method has been marked with #[must_use].",
+    required_update: Minor,
+
+    // TODO: Change the reference link to point to the cargo semver reference
+    //       once it has a section on attribute #[must_use].
+    reference_link: Some("https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute"),
+    query: r#"
+    {
+        CrateDiff {
+            current {
+                item {
+                    ... on ImplOwner {
+                        visibility_limit @filter(op: "=", value: ["$public"]) @output
+                        name @tag @output
+                        owner_type: __typename @tag
+
+                        importable_path {
+                            path @tag @output
+                        }
+
+                        inherent_impl {
+                            method {
+                                method_visibility: visibility_limit @filter(op: "=", value: ["$public"]) @output
+                                method_name: name @tag @output
+
+                                attribute {
+                                    new_attr: raw_attribute @output
+                                    content {
+                                        base @filter(op: "=", value: ["$must_use"])
+                                    }
+                                }
+
+                                span_: span @optional {
+                                    filename @output
+                                    begin_line @output
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+            baseline {
+                item {
+                    ... on ImplOwner {
+                        visibility_limit @filter(op: "=", value: ["$public"])
+                        name @filter(op: "=", value: ["%name"])
+                        __typename @filter(op: "=", value: ["%owner_type"])
+
+                        importable_path {
+                            path @filter(op: "=", value: ["%path"])
+                        }
+
+                        inherent_impl {
+                            method {
+                                visibility_limit @filter(op: "=", value: ["$public"])
+                                name @filter(op: "=", value: ["%method_name"])
+
+                                attribute @fold @transform(op: "count") @filter(op: "=", value: ["$zero"]) {
+                                    content {
+                                        base @filter(op: "=", value: ["$must_use"])
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "public": "public",
+        "must_use": "must_use",
+        "zero": 0,
+    },
+    error_message: "An inherent method is now #[must_use]. Downstream crates that did not use its return value will get a compiler lint.",
+    per_result_error_template: Some("inherent method {{join \"::\" path}}::{{method_name}} in {{span_filename}}:{{span_begin_line}}"),
+)

src/query.rs

@@ -424,6 +424,7 @@ add_lints!(
     function_unsafe_added,
     inherent_method_const_removed,
     inherent_method_missing,
+    inherent_method_must_use_added,
     inherent_method_unsafe_added,
     method_parameter_count_changed,
     sized_impl_removed,

test_crates/inherent_method_must_use_added/new/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+publish = false
+name = "inherent_method_must_use_added"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

test_crates/inherent_method_must_use_added/new/src/enum_inherent_method_must_use_added.rs

@@ -0,0 +1,82 @@
+pub enum EnumWithMustUseMethods {
+    Bar,
+}
+
+impl EnumWithMustUseMethods {
+
+    // These methods did not have the #[must_use] attribute in the old version.
+    // Addition of the attribute should be reported.
+
+    #[must_use]
+    pub fn MethodToMustUseMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MethodToMustUseMessageMethod(&self) {}
+
+
+    // These methods had the #[must_use] attribute in the old version. Changes of
+    // the attribute, including deletion, should not be reported.
+
+    pub fn MustUseMethodToMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MustUseMethodToMustUseMessageMethod(&self) {}
+
+
+    // These methods had the #[must_use] attribute in the old version.
+    // They also included the user-defined warning message. Changes of
+    // the attribute, including deletion, should not be reported.
+
+    pub fn MustUseMessageMethodToMethod(&self) {}
+
+    #[must_use]
+    pub fn MustUseMessageMethodToMustUseMethod(&self) {}
+
+    #[must_use = "Baz"]
+    pub fn MustUseMessageMethodToMustUseMessageMethod(&self) {}
+}
+
+
+// This public enum's inherent method did not have the #[must_use] attribute
+// in the old version. Because the method is private, adding the attribute
+// should NOT be reported.
+
+pub enum EnumWithPrivateMustUseMethods {
+    Bar,
+}
+
+impl EnumWithPrivateMustUseMethods {
+
+    #[must_use]
+    fn PrivateMethodToPrivateMustUseMethod(&self) {}
+}
+
+
+// This enum is private and adding #[must_use] to its inherent method
+// should NOT be reported.
+
+enum PrivateEnumWithMustUseMethods {
+    Bar,
+}
+
+impl PrivateEnumWithMustUseMethods {
+
+    #[must_use]
+    fn PrivateEnumMethodToPrivateEnumMustUseMethod(&self) {}
+}
+
+
+// This enum and its inherent method were added in the new version of the
+// crate, together with the method's attribute.
+// It should NOT be reported by this rule to avoid duplicate lints.
+// It should be reported as a new pub type that is part of the crate's API.
+
+pub enum NewEnumWithMustUseMethods {
+    Bar,
+}
+
+impl NewEnumWithMustUseMethods {
+
+    #[must_use]
+    pub fn NewEnumMustUseMethod(&self) {}
+}

test_crates/inherent_method_must_use_added/new/src/item_type_changed_inherent_method_must_use_added.rs

@@ -0,0 +1,163 @@
+// This test file pair contains test cases against items changing the type
+// between the old and new versions while their names and inherent methods
+// remain unchanged.
+// This can result in false-positives by reporting an addition of #[must_use]
+// to an inherent method while the ImplOwner of the method has changed, making
+// the new version method no more related to the old version method.
+
+pub struct EnumToStructWithMustUseMethods {}
+
+impl EnumToStructWithMustUseMethods {
+
+    #[must_use]
+    pub fn MethodToMustUseMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMethodToMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MustUseMethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMessageMethodToMethod(&self) {}
+
+    #[must_use]
+    pub fn MustUseMessageMethodToMustUseMethod(&self) {}
+
+    #[must_use = "Baz"]
+    pub fn MustUseMessageMethodToMustUseMessageMethod(&self) {}
+}
+
+
+pub union EnumToUnionWithMustUseMethods {
+    bar: usize,
+}
+
+impl EnumToUnionWithMustUseMethods {
+
+    #[must_use]
+    pub fn MethodToMustUseMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMethodToMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MustUseMethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMessageMethodToMethod(&self) {}
+
+    #[must_use]
+    pub fn MustUseMessageMethodToMustUseMethod(&self) {}
+
+    #[must_use = "Baz"]
+    pub fn MustUseMessageMethodToMustUseMessageMethod(&self) {}
+}
+
+
+pub enum StructToEnumWithMustUseMethods {
+    Bar,
+}
+
+impl StructToEnumWithMustUseMethods {
+
+    #[must_use]
+    pub fn MethodToMustUseMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMethodToMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MustUseMethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMessageMethodToMethod(&self) {}
+
+    #[must_use]
+    pub fn MustUseMessageMethodToMustUseMethod(&self) {}
+
+    #[must_use = "Baz"]
+    pub fn MustUseMessageMethodToMustUseMessageMethod(&self) {}
+}
+
+
+pub union StructToUnionWithMustUseMethods {
+    bar: usize,
+}
+
+impl StructToUnionWithMustUseMethods {
+
+    #[must_use]
+    pub fn MethodToMustUseMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMethodToMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MustUseMethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMessageMethodToMethod(&self) {}
+
+    #[must_use]
+    pub fn MustUseMessageMethodToMustUseMethod(&self) {}
+
+    #[must_use = "Baz"]
+    pub fn MustUseMessageMethodToMustUseMessageMethod(&self) {}
+}
+
+
+pub enum UnionToEnumWithMustUseMethods {
+    Bar,
+}
+
+impl UnionToEnumWithMustUseMethods {
+
+    #[must_use]
+    pub fn MethodToMustUseMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMethodToMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MustUseMethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMessageMethodToMethod(&self) {}
+
+    #[must_use]
+    pub fn MustUseMessageMethodToMustUseMethod(&self) {}
+
+    #[must_use = "Baz"]
+    pub fn MustUseMessageMethodToMustUseMessageMethod(&self) {}
+}
+
+
+pub struct UnionToStructWithMustUseMethods {}
+
+impl UnionToStructWithMustUseMethods {
+
+    #[must_use]
+    pub fn MethodToMustUseMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMethodToMethod(&self) {}
+
+    #[must_use = "Foo"]
+    pub fn MustUseMethodToMustUseMessageMethod(&self) {}
+
+    pub fn MustUseMessageMethodToMethod(&self) {}
+
+    #[must_use]
+    pub fn MustUseMessageMethodToMustUseMethod(&self) {}
+
+    #[must_use = "Baz"]
+    pub fn MustUseMessageMethodToMustUseMessageMethod(&self) {}
+}

test_crates/inherent_method_must_use_added/new/src/lib.rs

@@ -0,0 +1,10 @@
+// This crate's test cases were separated into smaller files for easier
+// management and debugging. 
+
+pub mod enum_inherent_method_must_use_added;
+
+pub mod struct_inherent_method_must_use_added;
+
+pub mod union_inherent_method_must_use_added;
+
+pub mod item_type_changed_inherent_method_must_use_added;