feat(eslint-plugin): [member-delimiter-style] Add an option 'multilineDetection' to treat types and interfaces as single line if the last member ends on the same line as the closing bracket

packages/eslint-plugin/docs/rules/member-delimiter-style.md

@@ -72,6 +72,7 @@ type Config = BaseConfig & {
     interface?: BaseConfig;
     typeLiteral?: BaseConfig;
   };
+  multilineDetection?: 'brackets' | 'last-member';
 };
 ```
 
@@ -86,14 +87,20 @@ Default config:
     "singleline": {
         "delimiter": "semi",
         "requireLast": false
-    }
+    },
+    "multilineDetection": "brackets"
 }
 ```
 
 `multiline` config only applies to multiline `interface`/`type` definitions.
 `singleline` config only applies to single line `interface`/`type` definitions.
 The two configs are entirely separate, and do not effect one another.
 
+`multilineDetection` determines what counts as multiline
+
+- `"brackets"` (default) any newlines in the type or interface make it multiline.
+- `"last-member"` if the last member of the interface is on the same line as the last bracket, it is counted as a single line.
+
 ### `delimiter`
 
 Accepts three values (or two for `singleline`):

packages/eslint-plugin/src/rules/member-delimiter-style.ts

@@ -21,6 +21,7 @@ type Config = BaseOptions & {
     typeLiteral?: BaseOptions;
     interface?: BaseOptions;
   };
+  multilineDetection?: 'brackets' | 'last-member';
 };
 type Options = [Config];
 type MessageIds =
@@ -82,6 +83,9 @@ export default util.createRule<Options, MessageIds>({
             },
             additionalProperties: false,
           },
+          multilineDetection: {
+            enum: ['brackets', 'last-member'],
+          },
         }),
         additionalProperties: false,
       },
@@ -97,6 +101,7 @@ export default util.createRule<Options, MessageIds>({
         delimiter: 'semi',
         requireLast: false,
       },
+      multilineDetection: 'brackets',
     },
   ],
   create(context, [options]) {
@@ -215,11 +220,21 @@ export default util.createRule<Options, MessageIds>({
     function checkMemberSeparatorStyle(
       node: TSESTree.TSInterfaceBody | TSESTree.TSTypeLiteral,
     ): void {
-      const isSingleLine = node.loc.start.line === node.loc.end.line;
-
       const members =
         node.type === AST_NODE_TYPES.TSInterfaceBody ? node.body : node.members;
 
+      let isSingleLine = node.loc.start.line === node.loc.end.line;
+      if (
+        options.multilineDetection === 'last-member' &&
+        !isSingleLine &&
+        members.length > 0
+      ) {
+        const lastMember = members[members.length - 1];
+        if (lastMember.loc.end.line === node.loc.end.line) {
+          isSingleLine = true;
+        }
+      }
+
       const typeOpts =
         node.type === AST_NODE_TYPES.TSInterfaceBody
           ? interfaceOptions

packages/eslint-plugin/tests/rules/member-delimiter-style.test.ts

@@ -705,6 +705,75 @@ type Bar = {
         },
       ],
     },
+    {
+      code: `
+type Foo = {a: {
+  b: true;
+}};
+      `,
+      options: [
+        {
+          multilineDetection: 'last-member',
+        },
+      ],
+    },
+    `
+type Foo = {a: {
+  b: true;
+};};
+    `,
+    {
+      code: `
+type Foo = {a: {
+  b: true;
+};};
+      `,
+      options: [
+        {
+          multilineDetection: 'brackets',
+        },
+      ],
+    },
+    {
+      code: `
+type Foo = {
+  a: {
+    b: true;
+  };
+};
+      `,
+      options: [
+        {
+          multilineDetection: 'last-member',
+        },
+      ],
+    },
+    {
+      code: `
+type Foo = {a: {
+  b: true;
+};};
+      `,
+      options: [
+        {
+          singleline: { delimiter: 'semi', requireLast: true },
+          multilineDetection: 'last-member',
+        },
+      ],
+    },
+    {
+      code: `
+type Foo = {
+
+};
+      `,
+      options: [
+        {
+          singleline: { delimiter: 'semi', requireLast: true },
+          multilineDetection: 'last-member',
+        },
+      ],
+    },
 
     {
       code: `
@@ -3365,5 +3434,101 @@ type Foo = {
         },
       ],
     },
+    {
+      code: `
+type Foo = {a: {
+  b: true;
+};};
+      `,
+      output: `
+type Foo = {a: {
+  b: true;
+}};
+      `,
+      options: [
+        {
+          multilineDetection: 'last-member',
+        },
+      ],
+      errors: [
+        {
+          messageId: 'unexpectedSemi',
+          line: 4,
+          column: 3,
+        },
+      ],
+    },
+    {
+      code: `
+type Foo = {a: {
+  b: true;
+}};
+      `,
+      output: `
+type Foo = {a: {
+  b: true;
+};};
+      `,
+      errors: [
+        {
+          messageId: 'expectedSemi',
+          line: 4,
+          column: 2,
+        },
+      ],
+    },
+    {
+      code: `
+type Foo = {
+  a: {
+    b: true;
+  }
+};
+      `,
+      output: `
+type Foo = {
+  a: {
+    b: true;
+  };
+};
+      `,
+      options: [
+        {
+          multilineDetection: 'last-member',
+        },
+      ],
+      errors: [
+        {
+          messageId: 'expectedSemi',
+          line: 5,
+          column: 4,
+        },
+      ],
+    },
+    {
+      code: `
+type Foo = {a: {
+  b: true;
+}};
+      `,
+      output: `
+type Foo = {a: {
+  b: true;
+};};
+      `,
+      options: [
+        {
+          singleline: { delimiter: 'semi', requireLast: true },
+          multilineDetection: 'last-member',
+        },
+      ],
+      errors: [
+        {
+          messageId: 'expectedSemi',
+          line: 4,
+          column: 2,
+        },
+      ],
+    },
   ],
 });