Add check for adding #[non_exhaustive] causing breakage.

scripts/regenerate_test_rustdocs.sh

@@ -19,6 +19,7 @@ mv "$RUSTDOC_OUTPUT" "$TARGET_DIR/baseline.json"
 
 # For each feature, re-run rustdoc with it enabled.
 features=(
+    'struct_marked_non_exhaustive'
     'struct_missing'
     'struct_pub_field_missing'
     'enum_missing'

semver_tests/Cargo.toml

@@ -8,6 +8,7 @@ edition = "2021"
 [dependencies]
 
 [features]
+struct_marked_non_exhaustive = []
 struct_missing = []
 struct_pub_field_missing = []
 enum_missing = []

semver_tests/src/test_cases.rs → semver_tests/src/test_cases/mod.rs

@@ -1,3 +1,5 @@
+pub mod non_exhaustive;
+
 /// Testing: <https://doc.rust-lang.org/cargo/reference/semver.html#item-remove>
 #[cfg(not(feature = "struct_missing"))]
 pub struct WillBeRemovedStruct;

semver_tests/src/test_cases/non_exhaustive.rs

@@ -0,0 +1,62 @@
+//! Adding `non_exhaustive` to a struct or enum variant is breaking because those items
+//! cannot be constructed outside of their defining crate:
+//!
+//! """
+/// Non-exhaustive types cannot be constructed outside of the defining crate:
+/// - Non-exhaustive variants (struct or enum variant) cannot be constructed with
+///   a StructExpression (including with functional update syntax).
+/// """
+/// From: <https://doc.rust-lang.org/reference/attributes/type_system.html#the-non_exhaustive-attribute>
+
+#[cfg(not(feature = "struct_marked_non_exhaustive"))]
+pub struct UnitStruct;
+
+#[cfg(feature = "struct_marked_non_exhaustive")]
+#[non_exhaustive]
+pub struct UnitStruct;
+
+#[cfg(not(feature = "struct_marked_non_exhaustive"))]
+pub struct TupleStruct(pub u64);
+
+#[cfg(feature = "struct_marked_non_exhaustive")]
+#[non_exhaustive]
+pub struct TupleStruct(pub u64);
+
+#[cfg(not(feature = "struct_marked_non_exhaustive"))]
+pub struct ExternallyConstructibleStruct {
+    pub foo: u64,
+}
+
+#[cfg(feature = "struct_marked_non_exhaustive")]
+#[non_exhaustive]
+pub struct ExternallyConstructibleStruct {
+    pub foo: u64,
+}
+
+// The private field within means this struct cannot be constructed
+// outside this crate, so #[non_exhaustive] won't change anything here.
+#[cfg(not(feature = "struct_marked_non_exhaustive"))]
+pub struct NonExternallyConstructibleTupleStruct(u64);
+
+#[cfg(feature = "struct_marked_non_exhaustive")]
+#[non_exhaustive]
+pub struct NonExternallyConstructibleTupleStruct(u64);
+
+#[cfg(not(feature = "struct_marked_non_exhaustive"))]
+pub struct NonExternallyConstructibleStruct {
+    pub foo: u64,
+
+    // This private field means this struct cannot be constructed with a struct literal
+    // from outside of this crate.
+    bar: u64,
+}
+
+#[cfg(feature = "struct_marked_non_exhaustive")]
+#[non_exhaustive]
+pub struct NonExternallyConstructibleStruct {
+    pub foo: u64,
+
+    // This private field means this struct cannot be constructed with a struct literal
+    // from outside of this crate.
+    bar: u64,
+}

src/adapter.rs

@@ -697,7 +697,7 @@ mod tests {
             std::fs::read_to_string(&format!("./src/test_data/{}.output.ron", query_name))
             .with_context(|| format!("Could not load src/test_data/{}.output.ron expected-outputs file, did you forget to add it?", query_name))
             .expect("failed to load expected outputs");
-        let expected_results: Vec<BTreeMap<String, FieldValue>> =
+        let mut expected_results: Vec<BTreeMap<String, FieldValue>> =
             ron::from_str(&expected_result_text)
                 .expect("could not parse expected outputs as ron format");
 
@@ -714,10 +714,21 @@ mod tests {
         );
         let results_iter = interpret_ir(adapter.clone(), parsed_query, args).unwrap();
 
-        let actual_results: Vec<BTreeMap<_, _>> = results_iter
+        let mut actual_results: Vec<BTreeMap<_, _>> = results_iter
             .map(|res| res.into_iter().map(|(k, v)| (k.to_string(), v)).collect())
             .collect();
 
+        // Reorder both vectors of results into a deterministic order that will compensate for
+        // nondeterminism in how the results are ordered.
+        let key_func = |elem: &BTreeMap<String, FieldValue>| {
+            (
+                elem["span_filename"].as_str().unwrap().to_owned(),
+                elem["span_begin_line"].as_usize().unwrap(),
+            )
+        };
+        expected_results.sort_unstable_by_key(key_func);
+        actual_results.sort_unstable_by_key(key_func);
+
         assert_eq!(expected_results, actual_results);
     }
 
@@ -737,5 +748,6 @@ mod tests {
         enum_variant_missing,
         struct_missing,
         struct_pub_field_missing,
+        struct_marked_non_exhaustive,
     );
 }

src/queries/struct_marked_non_exhaustive.ron

@@ -0,0 +1,66 @@
+SemverQuery(
+    id: "struct_marked_non_exhaustive",
+    human_readable_name: "struct marked #[non_exhaustive]",
+    description: "A publicly-visible struct has been marked #[non_exhaustive], but it was previously constructible using a struct literal outside its crate. The #[non_exhaustive] attribute disables that, so this is a major breaking change for code that depends on it.",
+    required_update: Major,
+
+    // TODO: Change the reference link once this cargo docs PR merges:
+    // https://github.com/rust-lang/cargo/pull/10877
+    //
+    // Change to this link:
+    // https://doc.rust-lang.org/cargo/reference/semver.html#attr-adding-non-exhaustive
+    reference_link: Some("https://doc.rust-lang.org/reference/attributes/type_system.html#the-non_exhaustive-attribute"),
+    query: r#"
+    {
+        CrateDiff {
+            baseline {
+                item {
+                    ... on Struct {
+                        visibility_limit @filter(op: "=", value: ["$public"]) @output
+                        name @output @tag
+                        struct_type @output
+                        attrs @filter(op: "not_contains", value: ["$non_exhaustive"])
+
+                        # Ensure the struct could previously be constructed outside of its crate
+                        # using a struct literal: it did not have any private fields.
+                        field @fold @transform(op: "count") @filter(op: "=", value: ["$zero"]) {
+                            visibility_limit @filter(op: "!=", value: ["$public"])
+                        }
+
+                        path {
+                            path @output @tag
+                        }
+
+                        span_: span @optional {
+                            filename @output
+                            begin_line @output
+                        }
+                    }
+                }
+            }
+            current @fold @transform(op: "count") @filter(op: ">", value: ["$zero"]) {
+                item {
+                    ... on Struct {
+                        visibility_limit @filter(op: "=", value: ["$public"])
+                        name @filter(op: "=", value: ["%name"])
+
+                        # The struct is now marked #[non_exhaustive] so it can't be constructed
+                        # using a struct literal outside of its crate. This is the breaking change.
+                        attrs @filter(op: "contains", value: ["$non_exhaustive"])
+
+                        path {
+                            path @filter(op: "=", value: ["%path"])
+                        }
+                    }
+                }
+            }
+        }
+    }"#,
+    arguments: {
+        "public": "public",
+        "non_exhaustive": "#[non_exhaustive]",
+        "zero": 0,
+    },
+    error_message: "A public struct has been marked #[non_exhaustive], which will prevent it from being constructed using a struct literal outside of its crate. It previously had no private fields, so a struct literal could be used to construct it outside its crate.",
+    per_result_error_template: Some("struct {{name}}, previously in file {{span_filename}}:{{span_begin_line}}"),
+)

src/test_data/enum_missing.output.ron

@@ -3,7 +3,7 @@
         "name": String("WillBeRemovedEnum"),
         "path": List([String("semver_tests"), String("test_cases"), String("WillBeRemovedEnum")]),
         "visibility_limit": String("public"),
-        "span_filename": String("src/test_cases.rs"),
-        "span_begin_line": Uint64(15),
+        "span_filename": String("src/test_cases/mod.rs"),
+        "span_begin_line": Uint64(17),
     }
 ]

src/test_data/enum_variant_missing.output.ron

@@ -4,7 +4,7 @@
         "variant_name": String("Bar"),
         "path": List([String("semver_tests"), String("test_cases"), String("VariantWillBeRemoved")]),
         "visibility_limit": String("public"),
-        "span_filename": String("src/test_cases.rs"),
-        "span_begin_line": Uint64(22),
+        "span_filename": String("src/test_cases/mod.rs"),
+        "span_begin_line": Uint64(24),
     }
 ]

src/test_data/struct_marked_non_exhaustive.output.ron

@@ -0,0 +1,41 @@
+[
+    {
+        "name": String("UnitStruct"),
+        "struct_type": String("unit"),
+        "path": List([
+            String("semver_tests"),
+            String("test_cases"),
+            String("non_exhaustive"),
+            String("UnitStruct"),
+        ]),
+        "span_filename": String("src/test_cases/non_exhaustive.rs"),
+        "span_begin_line": Uint64(12),
+        "visibility_limit": String("public"),
+    },
+    {
+        "name": String("TupleStruct"),
+        "struct_type": String("tuple"),
+        "path": List([
+            String("semver_tests"),
+            String("test_cases"),
+            String("non_exhaustive"),
+            String("TupleStruct"),
+        ]),
+        "span_filename": String("src/test_cases/non_exhaustive.rs"),
+        "span_begin_line": Uint64(19),
+        "visibility_limit": String("public"),
+    },
+    {
+        "name": String("ExternallyConstructibleStruct"),
+        "struct_type": String("plain"),
+        "path": List([
+            String("semver_tests"),
+            String("test_cases"),
+            String("non_exhaustive"),
+            String("ExternallyConstructibleStruct"),
+        ]),
+        "span_filename": String("src/test_cases/non_exhaustive.rs"),
+        "span_begin_line": Uint64(26),
+        "visibility_limit": String("public"),
+    }
+]

src/test_data/struct_missing.output.ron

@@ -4,7 +4,7 @@
         "struct_type": String("unit"),
         "path": List([String("semver_tests"), String("test_cases"), String("WillBeRemovedStruct")]),
         "visibility_limit": String("public"),
-        "span_filename": String("src/test_cases.rs"),
-        "span_begin_line": Uint64(3),
+        "span_filename": String("src/test_cases/mod.rs"),
+        "span_begin_line": Uint64(5),
     }
 ]

src/test_data/struct_pub_field_missing.output.ron

@@ -4,7 +4,7 @@
         "struct_type": String("plain"),
         "path": List([String("semver_tests"), String("test_cases"), String("FieldWillBeRemoved")]),
         "field_name": String("bar"),
-        "span_filename": String("src/test_cases.rs"),
-        "span_begin_line": Uint64(10),
+        "span_filename": String("src/test_cases/mod.rs"),
+        "span_begin_line": Uint64(12),
     }
 ]