feat: new eslint rule for restricting more than 1 interface (#3084)

* feat: new eslint rule for restricting more than 1 interface

* testing this

* minor

.eslintrc.json

@@ -82,7 +82,8 @@
         "@typescript-eslint/no-empty-interface": ["error"],
         "@typescript-eslint/no-inferrable-types": ["error"],
         "no-unused-expressions": ["error"],
-        "no-console": ["error", { "allow": [""] }]
+        "no-console": ["error", { "allow": [""] }],
+        "custom-rules/one-interface-per-file": "error"
       }
     },
     {

eslint-custom-rules/index.js

@@ -3,6 +3,7 @@ module.exports = {
       'prefer-deep-freeze': require('./rules/eslint-plugin-prefer-deep-freeze'),
       'space-before-it-blocks': require('./rules/eslint-plugin-space-before-it-blocks'),
       'prefer-jasmine-matchers': require('./rules/eslint-plugin-prefer-jasmine-matchers'),
-      'prefer-resolve-to-reject-with': require('./rules/eslint-plugin-prefer-resolve-to-reject-with')
+      'prefer-resolve-to-reject-with': require('./rules/eslint-plugin-prefer-resolve-to-reject-with'),
+      'one-interface-per-file': require('./rules/eslint-plugin-one-interface-per-file'),
     },
 };

eslint-custom-rules/rules/eslint-plugin-one-interface-per-file.js

@@ -0,0 +1,45 @@
+module.exports = {
+  meta: {
+    type: "suggestion",
+    docs: {
+      description: "Enforce only one TypeScript interface or type per file.",
+      category: "TypeScript",
+      recommended: true,
+    },
+    schema: [],
+  },
+
+  create: function(context) {
+    let interfaceCount = 0;
+    let typeCount = 0;
+
+    return {
+      TSInterfaceDeclaration: function(node) {
+        interfaceCount++;
+
+        if (interfaceCount > 1 || typeCount > 0) {
+          context.report({
+            node,
+            message: "Only one TypeScript interface or type is allowed per file.",
+          });
+        }
+      },
+
+      TSTypeAliasDeclaration: function(node) {
+        typeCount++;
+
+        if (typeCount > 1 || interfaceCount > 0) {
+          context.report({
+            node,
+            message: "Only one TypeScript interface or type is allowed per file.",
+          });
+        }
+      },
+
+      "Program:exit": function() {
+        interfaceCount = 0; // Reset the counters for the next file
+        typeCount = 0;
+      },
+    };
+  },
+};