feat: add lint struct_marked_non_exhaustive_changed_type (#963)

* implemented `struct_marked_non_exhaustive_changed_type`

* reworded some comments

* Apply suggestions from code review

Co-authored-by: Predrag Gruevski <[email protected]>

* renamed the lint to `non_exhaustive_struct_changed_type`

* fixed the lints not being ordered correctly

* fix: ran the testing

---------

Co-authored-by: Predrag Gruevski <[email protected]>

src/lints/constructible_struct_changed_type.ron

@@ -12,7 +12,7 @@ to make it an enum or union is a breaking change, since the new enum / union can
 with the same struct literal syntax.
 
 While struct literals can be used to create any exhaustive struct whose fields are all public, \
-structs with *any* (not *only*) public fields are handled in a different lint. \
+structs with *any* fields are handled in a different lints. \
 This lint covers the remaining edge case: exhaustive structs with no fields whatsoever.
 
 More info: https://github.com/obi1kenobi/cargo-semver-checks/issues/297
@@ -29,6 +29,7 @@ More info: https://github.com/obi1kenobi/cargo-semver-checks/issues/297
                         struct_type @output
 
                         # If the struct is non-exhaustive, it can't be constructed using a literal.
+                        # A struct having this is breaking via non_exhaustive_struct_changed_type instead.
                         attrs @filter(op: "not_contains", value: ["$non_exhaustive"])
 
                         # The struct must not have any fields.

src/lints/non_exhaustive_struct_changed_type.ron

@@ -0,0 +1,74 @@
+SemverQuery(
+    id: "non_exhaustive_struct_changed_type",
+    human_readable_name: "struct marked #[non_exhaustive] with no fields became an enum or union",
+    description: "A struct marked #[non_exhaustive] with no fields was converted into an enum or union, breaking pattern matching.",
+    required_update: Major,
+    lint_level: Deny,
+    reference_link: Some("https://internals.rust-lang.org/t/rest-patterns-foo-should-match-non-struct-types/21607"),
+    reference: Some(
+        r#"\
+Even if a struct does not have fields and is marked `#[non_exhaustive]`, pattern matching like
+`matches!(value, Example { .. })` is allowed outside the struct's own crate. \
+Changing such a struct into an enum or union will break such pattern matching.
+
+More info: https://github.com/obi1kenobi/cargo-semver-checks/issues/954
+"#
+    ),
+    query: r#"
+    {
+        CrateDiff {
+            baseline {
+                item {
+                    ... on Struct {
+                        struct_typename: __typename @tag @output
+                        visibility_limit @filter(op: "=", value: ["$public"]) @output
+                        struct_type @output
+
+                        # Requiring #[non_exhaustive] removes overlap with constructible_struct_changed_type
+                        attrs @filter(op: "contains", value: ["$non_exhaustive"])
+
+                        # Requiring at least one field removes overlap with struct_with_no_pub_fields_changed_type
+                        # That this is not a special case in said query is a limitation of our query engine
+                        field @fold @transform(op: "count") @filter(op: "=", value: ["$zero"])
+
+                        importable_path {
+                            path @output @tag
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+                    }
+                }
+            }
+            current {
+                item {
+                    ... on ImplOwner {
+                        current_typename: __typename @filter(op: "!=", value: ["%struct_typename"])
+                                                     @output
+                        visibility_limit @filter(op: "=", value: ["$public"])
+                        name @output
+
+                        importable_path {
+                            path @filter(op: "=", value: ["%path"])
+                            public_api @filter(op: "=", value: ["$true"])
+                        }
+
+                        span_: span @optional {
+                            filename @output
+                            begin_line @output
+                        }
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "public": "public",
+        "non_exhaustive": "#[non_exhaustive]",
+        "true": true,
+        "zero": 0,
+    },
+    error_message: "A struct marked #[non_exhaustive] with no fields was converted into an enum or union, breaking pattern matching",
+    per_result_error_template: Some("struct {{join \"::\" path}} became {{lowercase current_typename}} in file {{span_filename}}:{{span_begin_line}}"),
+    witness: (
+        hint_template: r#"matches!(value, {{join "::" path}} {..});"#,
+    ),
+)

src/lints/struct_with_no_pub_fields_changed_type.ron

@@ -31,7 +31,10 @@ More info: https://github.com/obi1kenobi/cargo-semver-checks/issues/954
                         }
 
                         # Ensure the struct does have non-pub fields
-                        # This prevents overlap with constructible_struct_changed_type
+                        #
+                        # This prevents overlap with constructible_struct_changed_type, but doing this requires
+                        # non_exhaustive_struct_changed_type instead. Merging into this lint is currently
+                        # impossible due the query engine limitation of not having OR-conditions.
                         field @fold @transform(op: "count") @filter(op: ">", value: ["$zero"])
 
                         importable_path {

src/query.rs

@@ -1049,6 +1049,7 @@ add_lints!(
     inherent_method_unsafe_added,
     method_parameter_count_changed,
     module_missing,
+    non_exhaustive_struct_changed_type,
     pub_module_level_const_missing,
     pub_module_level_const_now_doc_hidden,
     pub_static_missing,

test_crates/non_exhaustive_struct_changed_type/new/Cargo.toml

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

test_crates/non_exhaustive_struct_changed_type/new/src/lib.rs

@@ -0,0 +1,5 @@
+pub enum PubNonExhaustiveStructChangedToEnum {}
+
+pub union PubNonExhaustiveStructChangedToUnion {
+    foo: usize
+}

test_crates/non_exhaustive_struct_changed_type/old/Cargo.toml

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

test_crates/non_exhaustive_struct_changed_type/old/src/lib.rs

@@ -0,0 +1,5 @@
+#[non_exhaustive]
+pub struct PubNonExhaustiveStructChangedToEnum {}
+
+#[non_exhaustive]
+pub struct PubNonExhaustiveStructChangedToUnion {}

test_outputs/query_execution/non_exhaustive_struct_changed_type.snap

@@ -0,0 +1,75 @@
+---
+source: src/query.rs
+expression: "&query_execution_results"
+---
+{
+  "./test_crates/non_exhaustive_struct_changed_type/": [
+    {
+      "current_typename": String("Enum"),
+      "name": String("PubNonExhaustiveStructChangedToEnum"),
+      "path": List([
+        String("non_exhaustive_struct_changed_type"),
+        String("PubNonExhaustiveStructChangedToEnum"),
+      ]),
+      "span_begin_line": Uint64(1),
+      "span_filename": String("src/lib.rs"),
+      "struct_type": String("plain"),
+      "struct_typename": String("Struct"),
+      "visibility_limit": String("public"),
+    },
+    {
+      "current_typename": String("Union"),
+      "name": String("PubNonExhaustiveStructChangedToUnion"),
+      "path": List([
+        String("non_exhaustive_struct_changed_type"),
+        String("PubNonExhaustiveStructChangedToUnion"),
+      ]),
+      "span_begin_line": Uint64(3),
+      "span_filename": String("src/lib.rs"),
+      "struct_type": String("plain"),
+      "struct_typename": String("Struct"),
+      "visibility_limit": String("public"),
+    },
+  ],
+  "./test_crates/struct_becomes_enum/": [
+    {
+      "current_typename": String("Enum"),
+      "name": String("NonExhaustiveEmptyStructToEnum"),
+      "path": List([
+        String("struct_becomes_enum"),
+        String("NonExhaustiveEmptyStructToEnum"),
+      ]),
+      "span_begin_line": Uint64(82),
+      "span_filename": String("src/lib.rs"),
+      "struct_type": String("plain"),
+      "struct_typename": String("Struct"),
+      "visibility_limit": String("public"),
+    },
+    {
+      "current_typename": String("Enum"),
+      "name": String("NonExhaustiveFieldlessUnit"),
+      "path": List([
+        String("struct_becomes_enum"),
+        String("NonExhaustiveFieldlessUnit"),
+      ]),
+      "span_begin_line": Uint64(95),
+      "span_filename": String("src/lib.rs"),
+      "struct_type": String("unit"),
+      "struct_typename": String("Struct"),
+      "visibility_limit": String("public"),
+    },
+    {
+      "current_typename": String("Enum"),
+      "name": String("NonExhaustiveFieldlessTuple"),
+      "path": List([
+        String("struct_becomes_enum"),
+        String("NonExhaustiveFieldlessTuple"),
+      ]),
+      "span_begin_line": Uint64(100),
+      "span_filename": String("src/lib.rs"),
+      "struct_type": String("tuple"),
+      "struct_typename": String("Struct"),
+      "visibility_limit": String("public"),
+    },
+  ],
+}

test_outputs/witnesses/non_exhaustive_struct_changed_type.snap

@@ -0,0 +1,29 @@
+---
+source: src/query.rs
+description: "Lint `non_exhaustive_struct_changed_type` did not have the expected witness output.\nSee https://github.com/obi1kenobi/cargo-semver-checks/blob/main/CONTRIBUTING.md#testing-witnesses\nfor more information."
+expression: "&actual_witnesses"
+---
+[["./test_crates/non_exhaustive_struct_changed_type/"]]
+filename = 'src/lib.rs'
+begin_line = 1
+hint = 'matches!(value, non_exhaustive_struct_changed_type::PubNonExhaustiveStructChangedToEnum {..});'
+
+[["./test_crates/non_exhaustive_struct_changed_type/"]]
+filename = 'src/lib.rs'
+begin_line = 3
+hint = 'matches!(value, non_exhaustive_struct_changed_type::PubNonExhaustiveStructChangedToUnion {..});'
+
+[["./test_crates/struct_becomes_enum/"]]
+filename = 'src/lib.rs'
+begin_line = 82
+hint = 'matches!(value, struct_becomes_enum::NonExhaustiveEmptyStructToEnum {..});'
+
+[["./test_crates/struct_becomes_enum/"]]
+filename = 'src/lib.rs'
+begin_line = 95
+hint = 'matches!(value, struct_becomes_enum::NonExhaustiveFieldlessUnit {..});'
+
+[["./test_crates/struct_becomes_enum/"]]
+filename = 'src/lib.rs'
+begin_line = 100
+hint = 'matches!(value, struct_becomes_enum::NonExhaustiveFieldlessTuple {..});'