feat(eslint-plugin): no-unnecessary-condition (#116)

Closes #115 

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- Add the no-unnecessary-condition rule
- Improve the readme for starting up the project

Author: AntoineThibi

README.md

@@ -19,6 +19,9 @@ There is also an example app under `packages/example-app` whose goal is to demon
 
 - clone the project: `git clone https://github.com/bamlab/react-native-project-config`,
 - install the dependencies: `yarn install`,
+- build the eslint-plugin: `yarn workspace @bam.tech/eslint-plugin build`
+
+✅ Check : in the example-app in eslint-breaking-examples you should see the eslint errors.
 
 ## Modifying the project
 

example-app/eslint-breaking-examples/break-typescript-no-unnecessary-condition.ts

@@ -0,0 +1,9 @@
+// Save without formatting: [⌘ + K] > [S]
+
+// This should trigger one error breaking eslint-plugin-react-native:
+// @typescript-eslint/no-unnecessary-condition
+
+export const bar = (arg: string) => {
+  // arg can never be nullish, so ?. is unnecessary
+  return arg?.length;
+};

packages/eslint-plugin/docs/Testing.md

@@ -10,6 +10,14 @@ The example-app folder is located at the root of `react-native-project-config`.
 The goal of each file of example-app is to simulate the behavior of a rule or a set of rules, so that you can visually check it or by running the `yarn lint` command.
 When you add or remove a rule from the recommended config, please modify (or add/remove) the corresponding file in the example-app folder.
 
+## Adding a new rule
+
+In order to add a new rule, you must add it to the packages eslint-plugin, and then build it (it is in typescript) before seeing the changes in the example-app with the command:
+
+```bash
+yarn workspace @bam.tech/eslint-plugin build
+```
+
 ## Real example testing
 
 In order to test that your rule will be properly deployed, use another project, in which you install the eslint-plugin from your local files.

packages/eslint-plugin/lib/configs/recommended.ts

@@ -76,6 +76,7 @@ export const recommendedConfig = defineConfig({
         "no-return-await": "off", // Disable the base rule as it can report incorrect errors
         "@typescript-eslint/return-await": "error",
         "@typescript-eslint/no-floating-promises": "error",
+        "@typescript-eslint/no-unnecessary-condition": "error",
       },
     },
   ],