fix: version range handling in update_pkg function

.changeset/silly-donkeys-shout.md

@@ -0,0 +1,5 @@
+---
+"svelte-migrate": minor
+---
+
+fix: version range handling in update_pkg function

packages/migrate/migrations/sveltekit-2/migrate.spec.js

@@ -2,7 +2,8 @@ import { assert, test } from 'vitest';
 import {
 	transform_code,
 	update_svelte_config_content,
-	update_tsconfig_content
+	update_tsconfig_content,
+	update_pkg_json_content
 } from './migrate.js';
 import { read_samples } from '../../utils.js';
 
@@ -30,3 +31,22 @@ for (const sample of read_samples(new URL('./tsjs-samples.md', import.meta.url))
 		assert.equal(actual, sample.after);
 	});
 }
+
+test('Does not downgrade versions', () => {
+	const result = update_pkg_json_content(`{
+	"devDependencies": {
+		"@sveltejs/adapter-vercel": "^5.1.0",
+		"typescript": "github:idk"
+	}
+}`);
+	assert.equal(
+		result,
+		`{
+	"devDependencies": {
+		"@sveltejs/adapter-vercel": "^5.1.0",
+		"@sveltejs/vite-plugin-svelte": "^3.0.0",
+		"typescript": "github:idk"
+	}
+}`
+	);
+});

packages/migrate/utils.js

@@ -205,54 +205,65 @@ export function posixify(str) {
  * @param {Array<[string, string, string?, ('dependencies' | 'devDependencies')?]>} updates
  */
 export function update_pkg(content, updates) {
-	const indent = content.split('\n')[1].match(/^\s+/)?.[0] || '  ';
-	const pkg = JSON.parse(content);
-
-	/**
-	 * @param {string} name
-	 * @param {string} version
-	 * @param {string} [additional]
-	 * @param {'dependencies' | 'devDependencies' | undefined} [insert]
-	 */
-	function update_pkg(name, version, additional = '', insert) {
-		if (pkg.dependencies?.[name]) {
-			const existing_range = pkg.dependencies[name];
-
-			if (semver.validRange(existing_range) && !semver.subset(existing_range, version)) {
-				log_migration(`Updated ${name} to ${version} ${additional}`);
-				pkg.dependencies[name] = version;
-			}
-		}
-
-		if (pkg.devDependencies?.[name]) {
-			const existing_range = pkg.devDependencies[name];
-
-			if (semver.validRange(existing_range) && !semver.subset(existing_range, version)) {
-				log_migration(`Updated ${name} to ${version} ${additional}`);
-				pkg.devDependencies[name] = version;
-			}
-		}
-
-		if (insert && !pkg[insert]?.[name]) {
-			if (!pkg[insert]) pkg[insert] = {};
-
-			// Insert the property in sorted position without adjusting other positions so diffs are easier to read
-			const sorted_keys = Object.keys(pkg[insert]).sort();
-			const index = sorted_keys.findIndex((key) => name.localeCompare(key) === -1);
-			const insert_index = index !== -1 ? index : sorted_keys.length;
-			const new_properties = Object.entries(pkg[insert]);
-			new_properties.splice(insert_index, 0, [name, version]);
-			pkg[insert] = Object.fromEntries(new_properties);
-
-			log_migration(`Added ${name} version ${version} ${additional}`);
-		}
-	}
-
-	for (const update of updates) {
-		update_pkg(...update);
-	}
-
-	return JSON.stringify(pkg, null, indent);
+    const indent = content.split('\n')[1].match(/^\s+/)?.[0] || '  ';
+    const pkg = JSON.parse(content);
+
+    /**
+     * @param {string} name
+     * @param {string} version
+     * @param {string} [additional]
+     * @param {'dependencies' | 'devDependencies' | undefined} [insert]
+     */
+    function update_pkg(name, version, additional = '', insert) {
+        /**
+         * @param {string} type
+         */
+        const updateVersion = (type) => {
+            const existingRange = pkg[type]?.[name];
+
+            if (
+                existingRange &&
+                semver.validRange(existingRange) &&
+                !semver.subset(existingRange, version)
+            ) {
+                // Check if the new version range is an upgrade
+                const minExistingVersion = semver.minVersion(existingRange);
+                const minNewVersion = semver.minVersion(version);
+
+                if (
+                    minExistingVersion &&
+                    minNewVersion &&
+                    semver.gt(minNewVersion, minExistingVersion)
+                ) {
+                    log_migration(`Updated ${name} to ${version}`);
+                    pkg[type][name] = version;
+                }
+            }
+        };
+
+        updateVersion('dependencies');
+        updateVersion('devDependencies');
+
+        if (insert && !pkg[insert]?.[name]) {
+            if (!pkg[insert]) pkg[insert] = {};
+
+            // Insert the property in sorted position without adjusting other positions so diffs are easier to read
+            const sorted_keys = Object.keys(pkg[insert]).sort();
+            const index = sorted_keys.findIndex((key) => name.localeCompare(key) === -1);
+            const insert_index = index !== -1 ? index : sorted_keys.length;
+            const new_properties = Object.entries(pkg[insert]);
+            new_properties.splice(insert_index, 0, [name, version]);
+            pkg[insert] = Object.fromEntries(new_properties);
+
+            log_migration(`Added ${name} version ${version} ${additional}`);
+        }
+    }
+
+    for (const update of updates) {
+        update_pkg(...update);
+    }
+
+    return JSON.stringify(pkg, null, indent);
 }
 
 const logged_migrations = new Set();