codemods: implement core-imports codemod

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/codemods/package.json

@@ -26,9 +26,11 @@
   "dependencies": {
     "@backstage/cli-common": "0.1.1",
     "chalk": "^4.0.0",
-    "jscodeshift": "^0.12.0"
+    "jscodeshift": "^0.12.0",
+    "jscodeshift-add-imports": "^1.0.10"
   },
   "devDependencies": {
+    "@types/jscodeshift": "^0.11.0",
     "@types/node": "^14.14.32",
     "commander": "^6.1.0",
     "ts-node": "^9.1.1"

packages/codemods/transforms/core-imports.js

@@ -13,4 +13,74 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-console.log('hello');
+
+const addImports = require('jscodeshift-add-imports');
+const { resolve: resolvePath } = require('path');
+const fs = require('fs');
+
+function findExports(packageName) {
+  const packagePath = require.resolve(`${packageName}/package.json`);
+  const typesPath = resolvePath(packagePath, '../dist/index.d.ts');
+  const content = fs.readFileSync(typesPath, 'utf8');
+  const [, exportSymbols] = content.match(/export \{ (.*) \};/);
+  return exportSymbols
+    .split(', ')
+    .map(exported => exported.match(/.* as (.*)/)?.[1] || exported);
+}
+
+const symbolTable = {
+  '@backstage/core-app-api': findExports('@backstage/core-app-api'),
+  '@backstage/core-components': findExports('@backstage/core-components'),
+  '@backstage/core-plugin-api': findExports('@backstage/core-plugin-api'),
+};
+
+const reverseSymbolTable = Object.entries(symbolTable).reduce(
+  (table, [pkg, symbols]) => {
+    for (const symbol of symbols) {
+      table[symbol] = pkg;
+    }
+    return table;
+  },
+  {},
+);
+
+module.exports = (file, /** @type {import('jscodeshift').API} */ api) => {
+  const j = api.jscodeshift;
+  const root = j(file.source);
+
+  // Find all import statements of @backstage/core
+  const imports = root.find(j.ImportDeclaration, {
+    source: {
+      value: '@backstage/core',
+    },
+  });
+
+  // Then loop through all the import statement and collects each imported symbol
+  const importedSymbols = imports.nodes().flatMap(node =>
+    (node.specifiers || []).flatMap(specifier => ({
+      name: specifier.imported.name, // The symbol we're importing
+      local: specifier.local.name, // The local name, usually this is the same
+    })),
+  );
+
+  // Now that we gathered all the imports we want to add, we get rid of the old one
+  imports.remove();
+
+  // The convert the imports into actual import statements
+  const newImportStatements = importedSymbols.map(({ name, local }) => {
+    const targetPackage = reverseSymbolTable[name];
+    if (!targetPackage) {
+      throw new Error(`No target package found for import of ${name}`);
+    }
+
+    return j.importDeclaration(
+      [j.importSpecifier(j.identifier(name), j.identifier(local))],
+      j.literal(targetPackage),
+    );
+  });
+
+  // And add the new imports. `addImports` will take care of resolving duplicates
+  addImports(root, newImportStatements);
+
+  return root.toSource();
+};