feat(eslint-plugin): Add unified-signature rule

packages/eslint-plugin/README.md

@@ -129,5 +129,6 @@ Install [`eslint-config-prettier`](https://github.com/prettier/eslint-config-pre
 | [`@typescript-eslint/prefer-namespace-keyword`](./docs/rules/prefer-namespace-keyword.md)                 | Require the use of the `namespace` keyword instead of the `module` keyword to declare custom TypeScript modules. (`no-internal-module` from TSLint) | :heavy_check_mark: | :wrench: |
 | [`@typescript-eslint/restrict-plus-operands`](./docs/rules/restrict-plus-operands.md)                     | When adding two variables, operands must both be of type number or of type string. (`restrict-plus-operands` from TSLint)                           |                    |          |
 | [`@typescript-eslint/type-annotation-spacing`](./docs/rules/type-annotation-spacing.md)                   | Require consistent spacing around type annotations (`typedef-whitespace` from TSLint)                                                               | :heavy_check_mark: | :wrench: |
+| [`@typescript-eslint/unified-signatures`](./docs/rules/unified-signatures.md)                             | Warns for any two overloads that could be unified into one. (`unified-signatures` from TSLint)     |    |   |
 
 <!-- end rule list -->

packages/eslint-plugin/ROADMAP.md

@@ -1,10 +1,10 @@
 # Roadmap
 
-✅ (28) = done  
-🌟 (79) = in ESLint core  
-🔌 (33) = in another plugin  
-🌓 (16) = implementations differ or ESLint version is missing functionality  
-🛑 (70) = unimplemented
+✅ (29) = done
+🌟 (79) = in ESLint core
+🔌 (33) = in another plugin
+🌓 (16) = implementations differ or ESLint version is missing functionality
+🛑 (69) = unimplemented
 
 ## TSLint rules
 
@@ -33,7 +33,7 @@
 | [`promise-function-async`]        | 🛑  | N/A ([relevant plugin][plugin:promise])              |
 | [`typedef`]                       | 🛑  | N/A                                                  |
 | [`typedef-whitespace`]            | ✅  | [`@typescript-eslint/type-annotation-spacing`]       |
-| [`unified-signatures`]            | 🛑  | N/A                                                  |
+| [`unified-signatures`]            | ✅  | [`@typescript-eslint/unified-signatures`]            |
 
 ### Functionality
 
@@ -96,7 +96,7 @@
 | [`use-default-type-parameter`]       | 🛑  | N/A                                                                   |
 | [`use-isnan`]                        | 🌟  | [`use-isnan`][use-isnan]                                              |
 
-<sup>[1]</sup> The ESLint rule also supports silencing with an extra set of parens (`if ((foo = bar)) {}`)  
+<sup>[1]</sup> The ESLint rule also supports silencing with an extra set of parens (`if ((foo = bar)) {}`)
 <sup>[2]</sup> Missing private class member support. [`@typescript-eslint/no-unused-vars`] adds support for some TS-specific features.
 
 ### Maintainability
@@ -120,7 +120,7 @@
 | [`prefer-readonly`]          | 🛑  | N/A                                                |
 | [`trailing-comma`]           | 🌓  | [`comma-dangle`][comma-dangle] or [Prettier]       |
 
-<sup>[1]</sup> Only warns when importing deprecated symbols  
+<sup>[1]</sup> Only warns when importing deprecated symbols
 <sup>[2]</sup> Missing support for blank-line-delimited sections
 
 ### Style
@@ -179,7 +179,7 @@
 | [`variable-name`]                   | 🌟  | <sup>[2]</sup>                                                                      |
 | [`whitespace`]                      | 🔌  | Use [Prettier]                                                                      |
 
-<sup>[1]</sup> Recommended config: `["error", { blankLine: "always", prev: "*", next: "return" }]`  
+<sup>[1]</sup> Recommended config: `["error", { blankLine: "always", prev: "*", next: "return" }]`
 <sup>[2]</sup> [`camelcase`][camelcase], [`no-underscore-dangle`][no-underscore-dangle], [`id-blacklist`][id-blacklist], and/or [`id-match`][id-match]
 
 ## tslint-microsoft-contrib rules
@@ -245,10 +245,10 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
 | `use-named-parameter`                 | 🛑  | N/A                                                                    |
 | `use-simple-attributes`               | 🛑  | N/A                                                                    |
 
-<sup>[1]</sup> Enforces blank lines both at the beginning and end of a block  
-<sup>[2]</sup> Recommended config: `["error", "ForInStatement"]`  
-<sup>[3]</sup> Recommended config: `["error", "declaration", { "allowArrowFunctions": true }]`  
-<sup>[4]</sup> Recommended config: `["error", { "terms": ["BUG", "HACK", "FIXME", "LATER", "LATER2", "TODO"], "location": "anywhere" }]`  
+<sup>[1]</sup> Enforces blank lines both at the beginning and end of a block
+<sup>[2]</sup> Recommended config: `["error", "ForInStatement"]`
+<sup>[3]</sup> Recommended config: `["error", "declaration", { "allowArrowFunctions": true }]`
+<sup>[4]</sup> Recommended config: `["error", { "terms": ["BUG", "HACK", "FIXME", "LATER", "LATER2", "TODO"], "location": "anywhere" }]`
 <sup>[5]</sup> Does not check class fields.
 
 [insecure-random]: https://github.com/desktop/desktop/blob/master/eslint-rules/insecure-random.js
@@ -310,7 +310,7 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
 | `react-a11y-titles`                       | 🛑  | N/A                                                        |
 | `react-anchor-blank-noopener`             | 🛑  | N/A                                                        |
 
-<sup>[1]</sup> TSLint rule is more strict  
+<sup>[1]</sup> TSLint rule is more strict
 <sup>[2]</sup> ESLint rule only reports for click handlers
 
 [prettier]: https://prettier.io

packages/eslint-plugin/docs/rules/unified-signatures.md

@@ -0,0 +1,31 @@
+# Warns for any two overloads that could be unified into one by using a union or an optional/rest parameter. (unified-signatures)
+
+Warns for any two overloads that could be unified into one by using a union or an optional/rest parameter.
+
+## Rule Details
+
+This rule aims to keep the source code as maintanable as posible by reducing the amount of overloads.
+
+Examples of **incorrect** code for this rule:
+
+```ts
+function f(x: number): void;
+function f(x: string): void;
+```
+```ts
+f(): void;
+f(...x: number[]): void;
+```
+
+Examples of **correct** code for this rule:
+
+```ts
+function f(x: number | stting): void;
+```
+```ts
+function f(x?: ...number[]): void;
+```
+
+## Related to
+
+ - TSLint: ['unified-signatures`](https://palantir.github.io/tslint/rules/unified-signatures/)