Change behavior of lint to lint API specific breakage

.github/workflows/ci.yml

@@ -1329,7 +1329,7 @@ jobs:
       - name: Check output
         run: |
           cd semver
-          EXPECTED="$(echo -e "--- failure auto_trait_impl_removed: auto trait no longer implemented ---\n--- failure enum_variant_discriminant_changed: enum variant had its discriminant change value ---")"
+          EXPECTED="$(echo -e "--- failure auto_trait_impl_removed: auto trait no longer implemented ---\n--- failure enum_no_repr_variant_discriminant_changed: enum variant had its discriminant change value ---")"
           RESULT="$(cat output | grep failure)"
           diff <(echo "$RESULT") <(echo "$EXPECTED")
 
@@ -1361,7 +1361,7 @@ jobs:
       - name: Check output
         run: |
           cd semver
-          EXPECTED="$(echo -e "--- failure auto_trait_impl_removed: auto trait no longer implemented ---\n--- failure enum_variant_discriminant_changed: enum variant had its discriminant change value ---")"
+          EXPECTED="$(echo -e "--- failure auto_trait_impl_removed: auto trait no longer implemented ---\n--- failure enum_no_repr_variant_discriminant_changed: enum variant had its discriminant change value ---")"
           RESULT="$(cat output | grep failure)"
           diff <(echo "$RESULT") <(echo "$EXPECTED")
 

src/lints/enum_variant_discriminant_changed.ron → src/lints/enum_no_repr_variant_discriminant_changed.ron

@@ -1,11 +1,11 @@
 SemverQuery(
-    id: "enum_variant_discriminant_changed",
+    id: "enum_no_repr_variant_discriminant_changed",
     human_readable_name: "enum variant had its discriminant change value",
     description: "A public enum's variant had its discriminant changed from its previous value.",
-    reference: Some("The public enum's variant had its discriminant changed from its previous value. This can cause compatibility issues, which may break FFI use cases."),
+    reference: Some("A public enum's variant had its discriminant changed from its previous value, which breaks implementors relying on the discriminant value."),
     required_update: Major,
     lint_level: Deny,
-    reference_link: Some("https://doc.rust-lang.org/reference/items/enumerations.html#discriminants"),
+    reference_link: Some("https://doc.rust-lang.org/reference/items/enumerations.html#assigning-discriminant-values"),
     query: r#"
     {
         CrateDiff {
@@ -15,6 +15,12 @@ SemverQuery(
                         visibility_limit @filter(op: "=", value: ["$public"]) @output
                         enum_name: name @output @tag
 
+                        attribute @optional {
+                            content {
+                                base @filter(op: "!=", value: ["$repr"])
+                            }
+                        }
+
                         importable_path {
                             path @output @tag
                             public_api @filter(op: "=", value: ["$true"])
@@ -35,6 +41,12 @@ SemverQuery(
                         visibility_limit @filter(op: "=", value: ["$public"])
                         name @filter(op: "=", value: ["%enum_name"])
 
+                        attribute @optional {
+                            content {
+                                base @filter(op: "!=", value: ["$repr"])
+                            }
+                        }
+
                         importable_path {
                             path @filter(op: "=", value: ["%path"])
                             public_api @filter(op: "=", value: ["$true"])
@@ -58,8 +70,9 @@ SemverQuery(
     }"#,
     arguments: {
         "public": "public",
+        "repr": "repr",
         "true": true,
     },
-    error_message: "The public enum's variant had its discriminant changed from its previous value. This can cause compatibility issues, which may break FFI use cases.",
+    error_message: "The public enum's variant had its discriminant changed from its previous value. This breaks implementors that relied on the discriminant value.",
     per_result_error_template: Some("variant {{enum_name}}::{{variant_name}} {{old_value}} -> {{new_value}} in {{span_filename}}:{{span_begin_line}}"),
 )

src/query.rs

@@ -792,6 +792,7 @@ add_lints!(
     enum_marked_non_exhaustive,
     enum_missing,
     enum_must_use_added,
+    enum_no_repr_variant_discriminant_changed,
     enum_now_doc_hidden,
     enum_repr_int_changed,
     enum_repr_int_removed,
@@ -805,7 +806,6 @@ add_lints!(
     enum_tuple_variant_field_now_doc_hidden,
     enum_unit_variant_changed_kind,
     enum_variant_added,
-    enum_variant_discriminant_changed,
     enum_variant_marked_non_exhaustive,
     enum_variant_missing,
     exported_function_changed_abi,

test_crates/enum_variant_discriminant_changed/new/Cargo.toml → test_crates/enum_no_repr_variant_discriminant_changed/new/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 publish = false
-name = "enum_variant_discriminant_changed"
+name = "enum_no_repr_variant_discriminant_changed"
 version = "0.1.0"
 edition = "2021"
 

test_crates/enum_no_repr_variant_discriminant_changed/new/src/lib.rs

@@ -0,0 +1,50 @@
+// Explicit discriminant changed values. By doing so, it changed the implicit
+// discriminant's value as well, should be reported.
+pub enum ExplicitAndImplicitDiscriminantsAreChanged {
+    First = 2,
+    Second,
+    Third = 5,
+}
+
+// Discriminant changed to be doc hidden and explicit. Being doc hidden is not relevant
+// since it's still part of the public API, should be reported.
+pub enum DiscriminantBecomesDocHiddenAndExplicit {
+    First,
+    #[doc(hidden)]
+    Second = 2,
+}
+
+// Explicit discriminants changed values, but being private dominates, should not be
+// reported.
+enum PrivateEnum {
+    First = 10,
+    Second = 11,
+}
+
+// Discriminant changed value, but with repr, should not be reported as it involves ABI
+// breakage as well, and this is linted at *API* only breakage.
+#[repr(u8)]
+pub enum FieldlessWithDiscrimants {
+    First = 10,
+    Tuple(),
+    Struct {},
+    Unit,
+    Last = 21,
+}
+
+// Implicit discriminant value changed by becoming explicit, should not be reported as it involves
+// ABI breakage as well, and this is linted at *API* only breakage.
+#[repr(u8)]
+pub enum FieldlessChangesToExplicitDescriminant {
+    Tuple(),
+    Struct {},
+    Unit = 5,
+}
+
+// Variant `Struct` acquires a field. By doing so, it makes the enum not `well-defined`,
+// meaning it is not possible to do a numeric cast anymore on the enum, should not be reported.
+pub enum UnitOnlyBecomesUndefined {
+    First,
+    Second,
+    Struct { a: i64 },
+}

test_crates/enum_variant_discriminant_changed/old/Cargo.toml → test_crates/enum_no_repr_variant_discriminant_changed/old/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 publish = false
-name = "enum_variant_discriminant_changed"
+name = "enum_no_repr_variant_discriminant_changed"
 version = "0.1.0"
 edition = "2021"
 

test_crates/enum_no_repr_variant_discriminant_changed/old/src/lib.rs

@@ -0,0 +1,53 @@
+// My task is:
+// discriminant changed value but no repr (API only)
+// the enum does not have an explicit representation (no repr)
+// we want to be super sure the 4 lints are disjoint here -- we should never have multiple of them trigger on the same variant
+
+// Explicit discriminant changed values. By doing so, it changed the implicit
+// discriminant's value as well, should be reported.
+pub enum ExplicitAndImplicitDiscriminantsAreChanged {
+    First = 1,
+    Second,
+    Third = 5,
+}
+
+// Discriminant changed to be doc hidden and explicit. Being doc hidden is not relevant
+// since it's still part of the public API, should be reported.
+pub enum DiscriminantBecomesDocHiddenAndExplicit {
+    First,
+    Second,
+}
+
+// Explicit discriminants changed values, but being private dominates, should not be
+// reported.
+enum PrivateEnum {
+    First = 1,
+    Second = 2,
+}
+
+// Discriminant changed value, but with repr, should not be reported as it involves ABI
+// breakage as well, and this is linted at *API* only breakage.
+#[repr(u8)]
+pub enum FieldlessWithDiscrimants {
+    First = 10,
+    Tuple(),
+    Struct {},
+    Unit,
+    Last = 20,
+}
+
+// Implicit discriminant value changed by becoming explicit, should not be reported as it involves
+// ABI breakage as well, and this is linted at *API* only breakage.
+pub enum FieldlessChangesToExplicitDescriminant {
+    Tuple(),
+    Struct {},
+    Unit,
+}
+
+// Variant `Struct` acquires a field. By doing so, it makes the enum not `well-defined`,
+// meaning it is not possible to do a numeric cast anymore on the enum, should not be reported.
+pub enum UnitOnlyBecomesUndefined {
+    First,
+    Second,
+    Struct {},
+}

test_outputs/enum_variant_discriminant_changed.output.ron → test_outputs/enum_no_repr_variant_discriminant_changed.output.ron

@@ -1,14 +1,14 @@
 {
-    "./test_crates/enum_variant_discriminant_changed/": [
+    "./test_crates/enum_no_repr_variant_discriminant_changed/": [
         {
             "enum_name": String("ExplicitAndImplicitDiscriminantsAreChanged"),
             "new_value": String("2"),
             "old_value": String("1"),
             "path": List([
-                String("enum_variant_discriminant_changed"),
+                String("enum_no_repr_variant_discriminant_changed"),
                 String("ExplicitAndImplicitDiscriminantsAreChanged"),
             ]),
-            "span_begin_line": Uint64(4),
+            "span_begin_line": Uint64(3),
             "span_filename": String("src/lib.rs"),
             "variant_name": String("First"),
             "visibility_limit": String("public"),
@@ -18,36 +18,23 @@
             "new_value": String("3"),
             "old_value": String("2"),
             "path": List([
-                String("enum_variant_discriminant_changed"),
+                String("enum_no_repr_variant_discriminant_changed"),
                 String("ExplicitAndImplicitDiscriminantsAreChanged"),
             ]),
-            "span_begin_line": Uint64(4),
+            "span_begin_line": Uint64(3),
             "span_filename": String("src/lib.rs"),
             "variant_name": String("Second"),
             "visibility_limit": String("public"),
         },
-        {
-            "enum_name": String("ImplicitDiscriminantBecomesExplicit"),
-            "new_value": String("5"),
-            "old_value": String("2"),
-            "path": List([
-                String("enum_variant_discriminant_changed"),
-                String("ImplicitDiscriminantBecomesExplicit"),
-            ]),
-            "span_begin_line": Uint64(12),
-            "span_filename": String("src/lib.rs"),
-            "variant_name": String("Unit"),
-            "visibility_limit": String("public"),
-        },
         {
             "enum_name": String("DiscriminantBecomesDocHiddenAndExplicit"),
             "new_value": String("2"),
             "old_value": String("1"),
             "path": List([
-                String("enum_variant_discriminant_changed"),
+                String("enum_no_repr_variant_discriminant_changed"),
                 String("DiscriminantBecomesDocHiddenAndExplicit"),
             ]),
-            "span_begin_line": Uint64(20),
+            "span_begin_line": Uint64(11),
             "span_filename": String("src/lib.rs"),
             "variant_name": String("Second"),
             "visibility_limit": String("public"),

test_outputs/enum_struct_variant_field_added.output.ron

@@ -1,4 +1,17 @@
 {
+    "./test_crates/enum_no_repr_variant_discriminant_changed/": [
+        {
+            "enum_name": String("UnitOnlyBecomesUndefined"),
+            "field_name": String("a"),
+            "path": List([
+                String("enum_no_repr_variant_discriminant_changed"),
+                String("UnitOnlyBecomesUndefined"),
+            ]),
+            "span_begin_line": Uint64(49),
+            "span_filename": String("src/lib.rs"),
+            "variant_name": String("Struct"),
+        },
+    ],
     "./test_crates/enum_struct_field_hidden_from_public_api/": [
         {
             "enum_name": String("AddedVariantField"),