New: Add member-delimiter-style

Author: weirdpattern

README.md

@@ -62,3 +62,4 @@ Then configure the rules you want to use under the rules section.
 * [`typescript/member-ordering`](./docs/rules/member-ordering.md) — enforces a standard member declaration order. (`member-ordering` from TSLint)
 * [`typescript/no-unused-vars`](./docs/rules/no-unused-vars.md) — prevents TypeScript-specific constructs from being erroneously flagged as unused
 * [`typescript/adjacent-overload-signatures`](./docs/rules/adjacent-overload-signatures.md) — enforces member overloads to be consecutive.
+* [`typescript/member-delimiter-style`](./docs/rules/member-delimiter-style.md) - enforces a member delimiter style in interfaces and type literals.

docs/rules/member-delimiter-style.md

@@ -0,0 +1,350 @@
+# Enforces a member delimiter style in interfaces and type literals.
+
+Enforces a consistent member delimiter style in interfaces and type literals. There are three member delimiter styles primarily used in TypeScript:
+- Semicolon style (default, preferred in TypeScript).
+```ts
+interface Foo {
+    name: string;
+    greet(): void; // last semicolon can be ignored
+}
+
+type Bar = {
+    name: string;
+    greet(): void; // last semicolon can be ignored
+}
+```
+
+- Comma style (JSON style).
+```ts
+interface Foo {
+    name: string,
+    greet(): void, // last comma can be ignored
+}
+
+type Bar = {
+    name: string,
+    greet(): void, // last comma can be ignored
+}
+```
+
+- Linebreak style.
+```ts
+interface Foo {
+    name: string
+    greet(): void
+}
+
+type Bar = {
+    name: string
+    greet(): void
+}
+```
+
+The rule also enforces the presence of the delimiter in the last member of the interface and/or type literal.
+
+## Rule Details
+
+This rule aims to standardise the way interface and type literal members are delimited.
+
+## Options
+
+This rule, in its default state, does not require any argument, in which case a **semicolon** is used as a delimiter and **all members** require a delimiter.
+The rule can also take one or more of the following options:
+- `"delimiter": "semi"`, (default) use this to require a semicolon.
+- `"delimiter": "comma"`, use this to require a comma.
+- `"delimiter": "none"`, use this to require a linebreak.
+- `"requireLast": true`, (default) use this to require a delimiter for all members of the interface and/or type literal.
+- `"requireLast": false`, use this to ignore the last member of the interface and/or type literal.
+- `"overrides"`, overrides the default options for **interfaces** and **type literals**.
+
+### defaults
+Examples of **incorrect** code for this rule with the defaults `{ delimiter: "semi", requireLast: true }` or no option at all:
+```ts
+// missing semicolon delimiter
+interface Foo {
+    name: string
+    greet(): string
+}
+
+// using incorrect delimiter
+interface Bar {
+    name: string,
+    greet(): string,
+}
+
+// missing last member delimiter
+interface Baz {
+    name: string;
+    greet(): string
+}
+
+// missing semicolon delimiter
+type Foo = {
+    name: string
+    greet(): string
+}
+
+// using incorrect delimiter
+type Bar = {
+    name: string,
+    greet(): string,
+}
+
+// missing last member delimiter
+type Baz = {
+    name: string,
+    greet(): string
+}
+```
+
+Examples of **correct** code for this rule with the default `{ delimiter: "semi", requireLast: true }`:
+```ts
+interface Foo {
+    name: string;
+    greet(): string;
+}
+
+type Bar = {
+    name: string;
+    greet(): string;
+}
+```
+
+### delimiter - semi
+Examples of **incorrect** code for this rule with `{ delimiter: "semi" }`:
+```ts
+// missing semicolon delimiter
+interface Foo {
+    name: string
+    greet(): string
+}
+
+// using incorrect delimiter
+interface Bar {
+    name: string,
+    greet(): string,
+}
+```
+
+Examples of **correct** code for this rule with `{ delimiter: "semi" }`:
+```ts
+// with requireLast = true/false
+interface Foo {
+    name: string;
+    greet(): string;
+}
+
+type Bar = {
+    name: string;
+    greet(): string;
+}
+
+// with requireLast = false
+interface Foo {
+    name: string;
+    greet(): string
+}
+
+type Bar = {
+    name: string;
+    greet(): string
+}
+```
+
+### delimiter - comma
+Examples of **incorrect** code for this rule with `{ delimiter: "comma" }`:
+```ts
+// missing comma delimiter
+interface Foo {
+    name: string
+    greet(): string
+}
+
+// using incorrect delimiter
+interface Bar {
+    name: string;
+    greet(): string;
+}
+```
+
+Examples of **correct** code for this rule with `{ delimiter: "comma" }`:
+```ts
+// with requireLast = true/false
+interface Foo {
+    name: string,
+    greet(): string,
+}
+
+type Bar = {
+    name: string,
+    greet(): string,
+}
+
+// with requireLast = false
+interface Foo {
+    name: string,
+    greet(): string
+}
+
+type Bar = {
+    name: string,
+    greet(): string
+}
+```
+
+### delimiter - none
+Examples of **incorrect** code for this rule with `{ delimiter: "none" }`:
+```ts
+// using incorrect delimiter
+interface Foo {
+    name: string;
+    greet(): string;
+}
+
+// using incorrect delimiter
+interface Bar {
+    name: string,
+    greet(): string,
+}
+```
+
+Examples of **correct** code for this rule with `{ delimiter: "none" }`:
+```ts
+interface Foo {
+    name: string
+    greet(): string
+}
+
+type Bar = {
+    name: string
+    greet(): string
+}
+```
+
+### requireLast
+Examples of **incorrect** code for this rule with `{ requireLast: true }`:
+```ts
+// using incorrect delimiter
+interface Foo {
+    name: string;
+    greet(): string
+}
+
+// using incorrect delimiter
+interface Bar {
+    name: string,
+    greet(): string
+}
+```
+
+Examples of **correct** code for this rule with `{ requireLast: true }`:
+```ts
+interface Foo {
+    name: string;
+    greet(): string;
+}
+
+type Bar = {
+    name: string,
+    greet(): string,
+}
+```
+
+Examples of **correct** code for this rule with `{ requireLast: false }`:
+```ts
+interface Foo {
+    name: string
+    greet(): string
+}
+
+interface Bar {
+    name: string;
+    greet(): string
+}
+
+interface Baz {
+    name: string;
+    greet(): string;
+}
+
+type Foo = {
+    name: string
+    greet(): string
+}
+
+type Bar = {
+    name: string,
+    greet(): string
+}
+
+type Baz = {
+    name: string,
+    greet(): string,
+}
+```
+
+### overrides - interface
+Examples of **incorrect** code for this rule with `{ delimiter: "comma", requireLast: true, overrides: { interface: { delimiter: "semi" } } }`:
+```ts
+// expecting a semicolon
+interface Foo {
+    name: string,
+    greet(): string,
+}
+
+// this is fine, using default
+type Bar = {
+    name: string,
+    greet(): string,
+}
+```
+
+Examples of **correct** code for this rule with `{ delimiter: "comma", requireLast: true, overrides: { interface: { delimiter: "semi" } } }`:
+```ts
+// this is fine, using override
+interface Foo {
+    name: string;
+    greet(): string;
+}
+
+// this is fine, using default
+type Bar = {
+    name: string,
+    greet(): string,
+}
+```
+
+### overrides - typeLiteral
+Examples of **incorrect** code for this rule with `{ delimiter: "semi", requireLast: true, overrides: { typeLiteral: { delimiter: "comma", requireLast: false } } }`:
+```ts
+// this is fine, using default
+interface Foo {
+    name: string;
+    greet(): string;
+}
+
+// expecting a comma
+type Bar = {
+    name: string;
+    greet(): string
+}
+```
+
+Examples of **correct** code for this rule with `{ delimiter: "semi", requireLast: true, overrides: { typeLiteral: { delimiter: "comma", requireLast: false } } }`:
+```ts
+// this is fine, using default
+interface Foo {
+    name: string;
+    greet(): string;
+}
+
+// this is fine, using override
+type Bar = {
+    name: string,
+    greet(): string
+}
+```
+
+## When Not To Use It
+
+If you don't care about enforcing a consistent member delimiter in interfaces and type literals, then you will not need this rule.