feat(eslint-plugin): [no-redeclare] ignoreDeclarationMerge of enum+namespace

packages/eslint-plugin/docs/rules/no-redeclare.md

@@ -41,6 +41,7 @@ When set to `true`, the rule will ignore declaration merges between the followin
 - class + namespace
 - class + interface + namespace
 - function + namespace
+- enum + namespace
 
 Examples of **correct** code with `{ ignoreDeclarationMerge: true }`:
 

packages/eslint-plugin/src/rules/no-redeclare.ts

@@ -63,6 +63,10 @@ export default util.createRule<Options, MessageIds>({
       AST_NODE_TYPES.TSModuleDeclaration,
       AST_NODE_TYPES.FunctionDeclaration,
     ]);
+    const ENUM_DECLARATION_MERGE_NODES = new Set<AST_NODE_TYPES>([
+      AST_NODE_TYPES.TSEnumDeclaration,
+      AST_NODE_TYPES.TSModuleDeclaration,
+    ]);
 
     function* iterateDeclarations(variable: TSESLint.Scope.Variable): Generator<
       {
@@ -164,12 +168,33 @@ export default util.createRule<Options, MessageIds>({
             return;
           }
 
-          // there's more than one class declaration, which needs to be reported
+          // there's more than one function declaration, which needs to be reported
           for (const { identifier } of functionDecls) {
             yield { type: 'syntax', node: identifier, loc: identifier.loc };
           }
           return;
         }
+
+        if (
+          // enum + namespace merging
+          identifiers.every(({ parent }) =>
+            ENUM_DECLARATION_MERGE_NODES.has(parent.type),
+          )
+        ) {
+          const enumDecls = identifiers.filter(
+            ({ parent }) => parent.type === AST_NODE_TYPES.TSEnumDeclaration,
+          );
+          if (enumDecls.length === 1) {
+            // safe declaration merging
+            return;
+          }
+
+          // there's more than one enum declaration, which needs to be reported
+          for (const { identifier } of enumDecls) {
+            yield { type: 'syntax', node: identifier, loc: identifier.loc };
+          }
+          return;
+        }
       }
 
       for (const { identifier } of identifiers) {

packages/eslint-plugin/tests/rules/no-redeclare.test.ts

@@ -122,6 +122,13 @@ namespace A {}
       code: `
 interface A {}
 class A {}
+namespace A {}
+      `,
+      options: [{ ignoreDeclarationMerge: true }],
+    },
+    {
+      code: `
+enum A {}
 namespace A {}
       `,
       options: [{ ignoreDeclarationMerge: true }],
@@ -605,6 +612,23 @@ class A {}
     },
     {
       code: `
+enum A {}
+namespace A {}
+enum A {}
+      `,
+      options: [{ ignoreDeclarationMerge: true }],
+      errors: [
+        {
+          messageId: 'redeclared',
+          data: {
+            id: 'A',
+          },
+          line: 4,
+        },
+      ],
+    },
+    {
+      code: `
 function A() {}
 class A {}
 namespace A {}