New lint - detecting field removals from a struct variant in enum (ob…

…i1kenobi#156)

* Added first, untested code

* Changed tabs to spaces

* First nonworking test

* Fixed test

* Changed occurences of structvariant with struct_variant

* Improved descriptions

Co-authored-by: Predrag Gruevski <2348618+obi1kenobi@users.noreply.github.com>

semver_tests/Cargo.toml

@@ -17,6 +17,7 @@ enum_repr_int_removed = []
 enum_repr_c_removed = []
 enum_variant_added = []
 enum_variant_missing = []
+enum_struct_variant_field_missing = []
 function_missing = []
 inherent_method_missing = []
 sized_impl_removed = []

semver_tests/src/test_cases/enum_struct_variant_field_missing.rs

@@ -0,0 +1,19 @@
+pub enum Enum {
+    FieldWillBeMissing {
+        foo: usize,
+
+        /// Testing: <https://doc.rust-lang.org/cargo/reference/semver.html#item-remove>
+        #[cfg(not(feature = "enum_struct_variant_field_missing"))]
+        bar: usize,
+    }
+}
+
+/// This struct variant should not be reported by the `enum_struct_variant_field_missing` rule:
+/// it will be removed altogether, so the correct rule to catch it is
+/// the `enum_variant_missing` rule and not the rule for missing fields.
+pub enum IgnoredEnum {
+    #[cfg(not(feature = "enum_struct_variant_field_missing"))]
+    StructVariantWillBeMissing {
+        foo: usize,
+    }
+}

semver_tests/src/test_cases/mod.rs

@@ -5,6 +5,7 @@ pub mod enum_repr_int_changed;
 pub mod enum_repr_int_removed;
 pub mod enum_variant_added;
 pub mod enum_variant_missing;
+pub mod enum_struct_variant_field_missing;
 pub mod item_missing;
 pub mod non_exhaustive;
 pub mod sized_impl_removed;

src/queries/enum_struct_variant_field_missing.ron

@@ -0,0 +1,66 @@
+SemverQuery(
+    id: "enum_struct_variant_field_missing",
+    human_readable_name: "pub enum struct variant's field removed or renamed" ,
+    description: "An enum's struct variant has a field that is no longer available under its prior name.",
+    required_update: Major,
+    reference_link: Some("https://doc.rust-lang.org/cargo/reference/semver.html#item-remove"),
+    query: r#"
+    {
+        CrateDiff {
+            baseline {
+                item {
+                    ... on Enum {
+                        visibility_limit @filter(op: "=", value: ["$public"])
+                        enum_name: name @output @tag
+
+                        importable_path {
+                            path @output @tag
+                        }
+
+                        variant {
+                            ... on StructVariant {
+                                variant_name: name @output @tag
+
+                                field {
+                                    field_name: name @output @tag
+                                    span_: span @optional {
+                                        filename @output
+                                        begin_line @output
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+            current {
+                item {
+                    ... on Enum {
+                        visibility_limit @filter(op: "=", value: ["$public"])
+                        name @filter(op: "=", value: ["%enum_name"])
+
+                        importable_path {
+                            path @filter(op: "=", value: ["%path"])
+                        }
+
+                        variant {
+                            ... on StructVariant {
+                                name @filter(op: "=", value: ["%variant_name"])
+                                
+                                field @fold @transform(op: "count") @filter(op: "=", value: ["$zero"]) {
+                                    name @filter(op: "=", value: ["%field_name"])
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "public": "public",
+        "zero": 0,
+    },
+    error_message: "A publicly-visible enum has a struct variant whose field is no longer available under its prior name. It may have been renamed or removed entirely.",
+    per_result_error_template: Some("field {{field_name}} of variant {{enum_name}}::{{variant_name}}, previously in file {{span_filename}}:{{span_begin_line}}"),
+)

src/query.rs

@@ -85,6 +85,7 @@ impl SemverQuery {
             include_str!("./queries/enum_repr_int_removed.ron"),
             include_str!("./queries/enum_variant_added.ron"),
             include_str!("./queries/enum_variant_missing.ron"),
+            include_str!("./queries/enum_struct_variant_field_missing.ron"),
             include_str!("./queries/function_missing.ron"),
             include_str!("./queries/inherent_method_missing.ron"),
             include_str!("./queries/sized_impl_removed.ron"),
@@ -280,6 +281,7 @@ mod tests {
         enum_repr_int_removed,
         enum_variant_added,
         enum_variant_missing,
+        enum_struct_variant_field_missing,
         function_missing,
         inherent_method_missing,
         sized_impl_removed,

src/test_data/enum_struct_variant_field_missing.output.ron

@@ -0,0 +1,15 @@
+[
+    {
+        "enum_name": String("Enum"),
+        "variant_name": String("FieldWillBeMissing"),
+        "path": List([
+            String("semver_tests"),
+            String("test_cases"),
+            String("enum_struct_variant_field_missing"),
+            String("Enum"),
+        ]),
+        "field_name": String("bar"),
+        "span_filename": String("src/test_cases/enum_struct_variant_field_missing.rs"),
+        "span_begin_line": Uint64(7),
+    }
+]