feat: Add enum support with context-aware breaking change detection

src/diff_walker.rs

@@ -387,6 +387,39 @@ impl<F: FnMut(Change)> DiffWalker<F> {
         }
     }
 
+    fn diff_enum(&mut self, json_path: &str, lhs: &mut SchemaObject, rhs: &mut SchemaObject) {
+        let lhs_enum = lhs.enum_values.as_deref().unwrap_or(&[]);
+        let rhs_enum = rhs.enum_values.as_deref().unwrap_or(&[]);
+        let lhs_has_no_enum = lhs.enum_values.is_none();
+        let rhs_has_no_enum = rhs.enum_values.is_none();
+
+        // Find removed enum values (in lhs but not in rhs)
+        for lhs_value in lhs_enum {
+            if !rhs_enum.contains(lhs_value) {
+                (self.cb)(Change {
+                    path: json_path.to_owned(),
+                    change: ChangeKind::EnumRemove {
+                        removed: lhs_value.clone(),
+                        rhs_has_no_enum,
+                    },
+                });
+            }
+        }
+
+        // Find added enum values (in rhs but not in lhs)
+        for rhs_value in rhs_enum {
+            if !lhs_enum.contains(rhs_value) {
+                (self.cb)(Change {
+                    path: json_path.to_owned(),
+                    change: ChangeKind::EnumAdd {
+                        added: rhs_value.clone(),
+                        lhs_has_no_enum,
+                    },
+                });
+            }
+        }
+    }
+
     fn resolve_references(
         &self,
         lhs: &mut SchemaObject,
@@ -496,6 +529,7 @@ impl<F: FnMut(Change)> DiffWalker<F> {
         }
         self.diff_const(json_path, lhs, rhs);
         self.diff_format(json_path, lhs, rhs);
+        self.diff_enum(json_path, lhs, rhs);
         // If we split the types, we don't want to compare type-specific properties
         // because they are already compared in the `Self::diff_any_of`
         if !is_lhs_split && !is_rhs_split {

src/types.rs

@@ -124,6 +124,22 @@ pub enum ChangeKind {
         /// The new format value.
         new_format: String,
     },
+    /// An enum value has been added to the allowed values.
+    EnumAdd {
+        /// The value that was added to the enum.
+        added: serde_json::Value,
+        /// Whether the enum constraint was added (lhs had no enum).
+        /// If true, this is breaking as it adds a new constraint.
+        lhs_has_no_enum: bool,
+    },
+    /// An enum value has been removed from the allowed values.
+    EnumRemove {
+        /// The value that was removed from the enum.
+        removed: serde_json::Value,
+        /// Whether the entire enum constraint was removed (rhs has no enum).
+        /// If true, this is non-breaking as it relaxes the constraint.
+        rhs_has_no_enum: bool,
+    },
 }
 
 impl ChangeKind {
@@ -170,6 +186,12 @@ impl ChangeKind {
             Self::FormatAdd { .. } => true,
             Self::FormatRemove { .. } => false,
             Self::FormatChange { .. } => true,
+            // EnumAdd is breaking only if it adds a new enum constraint (lhs had no enum).
+            // Adding values to an existing enum is non-breaking (accepts more data).
+            Self::EnumAdd { lhs_has_no_enum, .. } => *lhs_has_no_enum,
+            // EnumRemove is breaking if removing values from a surviving enum constraint.
+            // Removing the entire enum constraint is non-breaking (accepts more data).
+            Self::EnumRemove { rhs_has_no_enum, .. } => !rhs_has_no_enum,
         }
     }
 }

tests/fixtures/enum/add.json

@@ -0,0 +1,10 @@
+{
+  "lhs": {
+    "type": "string",
+    "enum": ["error", "warning", "info"]
+  },
+  "rhs": {
+    "type": "string",
+    "enum": ["error", "warning", "info", "debug"]
+  }
+}

tests/fixtures/enum/add_and_remove.json

@@ -0,0 +1,10 @@
+{
+  "lhs": {
+    "type": "string",
+    "enum": ["error", "warning", "debug"]
+  },
+  "rhs": {
+    "type": "string",
+    "enum": ["error", "info", "debug"]
+  }
+}

tests/fixtures/enum/add_constraint.json

@@ -0,0 +1,9 @@
+{
+  "lhs": {
+    "type": "string"
+  },
+  "rhs": {
+    "type": "string",
+    "enum": ["error", "warning", "info"]
+  }
+}

tests/fixtures/enum/mixed_types.json

@@ -0,0 +1,8 @@
+{
+  "lhs": {
+    "enum": ["error", 1, null, true]
+  },
+  "rhs": {
+    "enum": ["error", 1, null, true, "warning"]
+  }
+}

tests/fixtures/enum/number_values.json

@@ -0,0 +1,10 @@
+{
+  "lhs": {
+    "type": "integer",
+    "enum": [1, 2, 3]
+  },
+  "rhs": {
+    "type": "integer",
+    "enum": [1, 2, 3, 4]
+  }
+}

tests/fixtures/enum/real_world_event_type.json

@@ -0,0 +1,10 @@
+{
+  "lhs": {
+    "type": "string",
+    "enum": ["expectct", "expectstaple", "transaction", "default"]
+  },
+  "rhs": {
+    "type": "string",
+    "enum": ["expectct", "expectstaple", "transaction", "default", "generic"]
+  }
+}

tests/fixtures/enum/remove.json

@@ -0,0 +1,10 @@
+{
+  "lhs": {
+    "type": "string",
+    "enum": ["error", "warning", "info", "debug"]
+  },
+  "rhs": {
+    "type": "string",
+    "enum": ["error", "warning", "info"]
+  }
+}

tests/fixtures/enum/remove_constraint.json

@@ -0,0 +1,9 @@
+{
+  "lhs": {
+    "type": "string",
+    "enum": ["error", "warning", "info"]
+  },
+  "rhs": {
+    "type": "string"
+  }
+}

tests/fixtures/enum/unchanged.json

@@ -0,0 +1,10 @@
+{
+  "lhs": {
+    "type": "string",
+    "enum": ["error", "warning", "info"]
+  },
+  "rhs": {
+    "type": "string",
+    "enum": ["error", "warning", "info"]
+  }
+}

tests/snapshots/test__from_fixtures@enum__add.json.snap

@@ -0,0 +1,29 @@
+---
+source: tests/test.rs
+assertion_line: 12
+expression: diff
+info:
+  lhs:
+    enum:
+      - error
+      - warning
+      - info
+    type: string
+  rhs:
+    enum:
+      - error
+      - warning
+      - info
+      - debug
+    type: string
+input_file: tests/fixtures/enum/add.json
+---
+[
+    Change {
+        path: "",
+        change: EnumAdd {
+            added: String("debug"),
+            lhs_has_no_enum: false,
+        },
+    },
+]

tests/snapshots/test__from_fixtures@enum__add_and_remove.json.snap

@@ -0,0 +1,35 @@
+---
+source: tests/test.rs
+assertion_line: 12
+expression: diff
+info:
+  lhs:
+    enum:
+      - error
+      - warning
+      - debug
+    type: string
+  rhs:
+    enum:
+      - error
+      - info
+      - debug
+    type: string
+input_file: tests/fixtures/enum/add_and_remove.json
+---
+[
+    Change {
+        path: "",
+        change: EnumRemove {
+            removed: String("warning"),
+            rhs_has_no_enum: false,
+        },
+    },
+    Change {
+        path: "",
+        change: EnumAdd {
+            added: String("info"),
+            lhs_has_no_enum: false,
+        },
+    },
+]

tests/snapshots/test__from_fixtures@enum__add_constraint.json.snap

@@ -0,0 +1,38 @@
+---
+source: tests/test.rs
+assertion_line: 12
+expression: diff
+info:
+  lhs:
+    type: string
+  rhs:
+    enum:
+      - error
+      - warning
+      - info
+    type: string
+input_file: tests/fixtures/enum/add_constraint.json
+---
+[
+    Change {
+        path: "",
+        change: EnumAdd {
+            added: String("error"),
+            lhs_has_no_enum: true,
+        },
+    },
+    Change {
+        path: "",
+        change: EnumAdd {
+            added: String("warning"),
+            lhs_has_no_enum: true,
+        },
+    },
+    Change {
+        path: "",
+        change: EnumAdd {
+            added: String("info"),
+            lhs_has_no_enum: true,
+        },
+    },
+]

tests/snapshots/test__from_fixtures@enum__mixed_types.json.snap

@@ -0,0 +1,29 @@
+---
+source: tests/test.rs
+assertion_line: 12
+expression: diff
+info:
+  lhs:
+    enum:
+      - error
+      - 1
+      - ~
+      - true
+  rhs:
+    enum:
+      - error
+      - 1
+      - ~
+      - true
+      - warning
+input_file: tests/fixtures/enum/mixed_types.json
+---
+[
+    Change {
+        path: "",
+        change: EnumAdd {
+            added: String("warning"),
+            lhs_has_no_enum: false,
+        },
+    },
+]

tests/snapshots/test__from_fixtures@enum__number_values.json.snap

@@ -0,0 +1,29 @@
+---
+source: tests/test.rs
+assertion_line: 12
+expression: diff
+info:
+  lhs:
+    enum:
+      - 1
+      - 2
+      - 3
+    type: integer
+  rhs:
+    enum:
+      - 1
+      - 2
+      - 3
+      - 4
+    type: integer
+input_file: tests/fixtures/enum/number_values.json
+---
+[
+    Change {
+        path: "",
+        change: EnumAdd {
+            added: Number(4),
+            lhs_has_no_enum: false,
+        },
+    },
+]

tests/snapshots/test__from_fixtures@enum__real_world_event_type.json.snap

@@ -0,0 +1,31 @@
+---
+source: tests/test.rs
+assertion_line: 12
+expression: diff
+info:
+  lhs:
+    enum:
+      - expectct
+      - expectstaple
+      - transaction
+      - default
+    type: string
+  rhs:
+    enum:
+      - expectct
+      - expectstaple
+      - transaction
+      - default
+      - generic
+    type: string
+input_file: tests/fixtures/enum/real_world_event_type.json
+---
+[
+    Change {
+        path: "",
+        change: EnumAdd {
+            added: String("generic"),
+            lhs_has_no_enum: false,
+        },
+    },
+]