Introduce custom rules for i18n imports (#67)

Before:

- `import i18n from discourse-common/helpers/i18n;` -> `i18n()`
- `import I18n from "discourse-i18n";` -> `I18n.t()`
- `import I18n from "i18n";` -> `I18n.t()`

After:

- `import { i18n } from "discourse-i18n";` -> `i18n()`

These rules remain disabled by default. We can enable them by default once discourse/discourse@d606ac3d8e is widely available.

lint-configs/eslint-rules/i18n-import-location.mjs

@@ -0,0 +1,64 @@
+import { fixImport } from "./utils/fix-import.mjs";
+
+export default {
+  meta: {
+    type: "suggestion",
+    docs: {
+      description:
+        "disallow imports from 'i18n' and replace with 'discourse-i18n'",
+      category: "Best Practices",
+      recommended: false,
+    },
+    fixable: "code",
+    schema: [], // no options
+  },
+  create(context) {
+    return {
+      ImportDeclaration(node) {
+        if (node.source.value.toLowerCase() === "i18n") {
+          context.report({
+            node,
+            message:
+              "Import from 'i18n' is not allowed. Use 'discourse-i18n' instead.",
+            fix(fixer) {
+              return fixer.replaceText(node.source, "'discourse-i18n'");
+            },
+          });
+        }
+
+        if (
+          node.source.value.toLowerCase() === "discourse-common/helpers/i18n"
+        ) {
+          context.report({
+            node,
+            message:
+              "Import from 'discourse-common/helpers/i18n' is not allowed. Use 'discourse-i18n' instead.",
+            fix(fixer) {
+              const existingImport = context
+                .getSourceCode()
+                .ast.body.find(
+                  (n) =>
+                    n.type === "ImportDeclaration" &&
+                    n.source.value === "discourse-i18n"
+                );
+
+              if (existingImport) {
+                return [
+                  fixer.remove(node),
+                  fixImport(fixer, existingImport, {
+                    namedImportsToAdd: ["i18n"],
+                  }),
+                ];
+              } else {
+                return fixer.replaceText(
+                  node,
+                  `import { i18n } from 'discourse-i18n';`
+                );
+              }
+            },
+          });
+        }
+      },
+    };
+  },
+};

lint-configs/eslint-rules/i18n-t.mjs

@@ -0,0 +1,91 @@
+import { fixImport } from "./utils/fix-import.mjs";
+
+export default {
+  meta: {
+    type: "suggestion",
+    docs: {
+      description: "Use i18n(...) instead of 'I18n.t(...)'.",
+      category: "Best Practices",
+      recommended: false,
+    },
+    fixable: "code",
+    schema: [], // no options
+  },
+  create(context) {
+    const sourceCode = context.sourceCode ?? context.getSourceCode();
+    let alreadyFixedImport = false;
+
+    return {
+      MemberExpression(node) {
+        const isI18nT =
+          node.object.name === "I18n" && node.property.name === "t";
+        if (!isI18nT) {
+          return;
+        }
+
+        let scope = sourceCode.getScope(node);
+        let variable;
+        while (scope && !variable) {
+          variable = scope.variables.find((v) => v.name === "I18n");
+          scope = scope.upper;
+        }
+
+        if (!variable) {
+          return;
+        }
+
+        const i18nDefaultImport = variable.defs.find(
+          (d) =>
+            d.type === "ImportBinding" &&
+            d.node.type === "ImportDefaultSpecifier" &&
+            d.node.parent.source.value === "discourse-i18n"
+        );
+
+        if (!i18nDefaultImport) {
+          // I18n imported from elsewhere... weird!
+          return;
+        }
+
+        context.report({
+          node,
+          message: "Use 'i18n(...)' instead of 'I18n.t(...)'.",
+          fix(fixer) {
+            const fixes = [];
+
+            // Replace I18n.t with i18n
+            fixes.push(fixer.replaceText(node, `i18n`));
+
+            if (!alreadyFixedImport) {
+              const importDeclaration = i18nDefaultImport.node.parent;
+              const i18nSpecifier = importDeclaration.specifiers.find(
+                (specifier) =>
+                  specifier.type === "ImportSpecifier" &&
+                  specifier.imported.name === "i18n"
+              );
+
+              // Check if I18n is used elsewhere
+              const shouldRemoveDefaultImport = !variable.references.some(
+                (ref) =>
+                  ref.identifier.parent.type !== "MemberExpression" ||
+                  ref.identifier.parent.property.name !== "t"
+              );
+
+              if (!i18nSpecifier || shouldRemoveDefaultImport) {
+                fixes.push(
+                  fixImport(fixer, importDeclaration, {
+                    shouldHaveDefaultImport: !shouldRemoveDefaultImport,
+                    namedImportsToAdd: ["i18n"],
+                  })
+                );
+              }
+
+              alreadyFixedImport = true;
+            }
+
+            return fixes;
+          },
+        });
+      },
+    };
+  },
+};

lint-configs/eslint-rules/utils/fix-import.mjs

@@ -0,0 +1,69 @@
+/**
+ * Fix an import declaration
+ *
+ * @param {ASTNode} importDeclarationNode - The AST node representing the import declaration.
+ * @param {Object} options - Options for modifying the import statement.
+ * @param {boolean} options.shouldHaveDefaultImport - Whether the import should include a default import.
+ * @param {string[]} options.namedImportsToAdd - Named imports to add to the import statement.
+ * @param {string[]} options.namedImportsToRemove - Named imports to remove from the import statement.
+ */
+export function fixImport(
+  fixer,
+  importDeclarationNode,
+  { shouldHaveDefaultImport, namedImportsToAdd = [], namedImportsToRemove = [] }
+) {
+  const existingSpecifiers = importDeclarationNode.specifiers;
+  const existingDefaultImport = existingSpecifiers.find(
+    (specifier) => specifier.type === "ImportDefaultSpecifier"
+  );
+
+  // Map existing named imports to their local names
+  const existingNamedImports = existingSpecifiers
+    .filter((specifier) => specifier.type === "ImportSpecifier")
+    .reduce((acc, specifier) => {
+      acc[specifier.imported.name] = specifier.local.name;
+      return acc;
+    }, {});
+
+  // Determine final default import
+  let finalDefaultImport;
+  if (shouldHaveDefaultImport === undefined) {
+    finalDefaultImport = existingDefaultImport
+      ? existingDefaultImport.local.name
+      : null;
+  } else if (shouldHaveDefaultImport) {
+    finalDefaultImport = existingDefaultImport
+      ? existingDefaultImport.local.name
+      : shouldHaveDefaultImport;
+  } else {
+    finalDefaultImport = null;
+  }
+
+  // Determine final named imports, preserving aliases
+  const finalNamedImports = Array.from(
+    new Set([
+      ...Object.entries(existingNamedImports)
+        .filter(([imported]) => !namedImportsToRemove.includes(imported))
+        .map(([imported, local]) =>
+          imported === local ? imported : `${imported} as ${local}`
+        ),
+      ...namedImportsToAdd,
+    ])
+  );
+
+  // Construct the new import statement
+  let newImportStatement = "import ";
+  if (finalDefaultImport) {
+    newImportStatement += `${finalDefaultImport}`;
+    if (finalNamedImports.length > 0) {
+      newImportStatement += ", ";
+    }
+  }
+  if (finalNamedImports.length > 0) {
+    newImportStatement += `{ ${finalNamedImports.join(", ")} }`;
+  }
+  newImportStatement += ` from '${importDeclarationNode.source.value}';`;
+
+  // Replace the entire import declaration
+  return fixer.replaceText(importDeclarationNode, newImportStatement);
+}

lint-configs/eslint.mjs

@@ -9,6 +9,8 @@ import QUnitRecommended from "eslint-plugin-qunit/configs/recommended";
 import SimpleImportSort from "eslint-plugin-simple-import-sort";
 import SortClassMembers from "eslint-plugin-sort-class-members";
 import globals from "globals";
+import i18nImport from "./eslint-rules/i18n-import-location.mjs";
+import i18nT from "./eslint-rules/i18n-t.mjs";
 
 // Copied from "ember-template-imports/lib/utils"
 const TEMPLATE_TAG_PLACEHOLDER = "__GLIMMER_TEMPLATE";
@@ -85,6 +87,12 @@ export default [
       "decorator-position": DecoratorPosition,
       "simple-import-sort": SimpleImportSort,
       qunit: QUnitPlugin,
+      discourse: {
+        rules: {
+          "i18n-import-location": i18nImport,
+          "i18n-t": i18nT,
+        },
+      },
     },
     rules: {
       "block-scoped-var": "error",
@@ -249,6 +257,10 @@ export default [
           ],
         },
       ],
+      // TODO: enable by default once this commit is available widely
+      // https://github.com/discourse/discourse/commit/d606ac3d8e
+      // "discourse/i18n-import-location": ["error"],
+      // "discourse/i18n-t": ["error"],
     },
   },
   {

lint-configs/package.json

@@ -21,6 +21,9 @@
     },
     "./template-lint": {
       "require": "./template-lint.config.cjs"
+    },
+    "./eslint-discourse/*": {
+      "require": "./eslint-discourse/*.cjs"
     }
   },
   "scripts": {