Programmatic options passed to `register` are always ignored.

[eliellis]

Due to the below if condition, introduced in #694, if options are passed to register programmatically (e.g. register({ ...customOptions })), they will be ignored in favor of either the results from readDefaultTsConfig or options gathered directly by swc from a nearby .swcrc file when process.env.SWCRC = 'true'.

swc-node/packages/register/register.ts

Lines 108 to 110 in ba8f60d

	if (!process.env.SWCRC) {
	options = readDefaultTsConfig()
	}

In cases where SWCRC is not true (unset, etc.), the configuration returned from readDefaultTsConfig is taken even if options are passed to register, meaning the passed options are altogether ignored.

I believe in this specific circumstance, the intuition would be for options passed to register to be used $iif$ they were given && !process.env.SWCRC.

Unless I am totally off-base here, I think the body of the if can be changed to (or something similar):

if (!process.env.SWCRC) { 
   options = Object.keys(options).length ? options : readDefaultTsConfig() 
} 

Where when process.env.SWCRC is falsy, we prefer any programmatically specified options before trying to read a tsconfig.json file. With this, I think the scenario above should be accounted for appropriately, while also not breaking what was fixed in #694.

---

For anyone running into this currently, using patch-package with the below diff, I was able to quickly fix this for 1.6.6

diff --git a/node_modules/@swc-node/register/lib/register.js b/node_modules/@swc-node/register/lib/register.js
index 7d4cfd8..1a8eab1 100644
--- a/node_modules/@swc-node/register/lib/register.js
+++ b/node_modules/@swc-node/register/lib/register.js
@@ -88,7 +88,7 @@ function compile(sourcecode, filename, options, async = false) {
 exports.compile = compile;
 function register(options = {}, hookOpts = {}) {
     if (!process.env.SWCRC) {
-        options = (0, read_default_tsconfig_1.readDefaultTsConfig)();
+        options = Object.keys(options).length ? options : (0, read_default_tsconfig_1.readDefaultTsConfig)();
     }
     options.module = ts.ModuleKind.CommonJS;
     (0, sourcemap_support_1.installSourceMapSupport)();

---

A more detailed and interactive reproduction can be seen here.

[wSedlacek]

Thank you so much. This patch allows me to update past 1.5.4

[eliellis]

With the recent updates to @swc-node/core, assuming your @swc-node/register dependency is still pinned to 1.6.6, here is the new patch to keep everything working:

diff --git a/node_modules/@swc-node/register/lib/read-default-tsconfig.js b/node_modules/@swc-node/register/lib/read-default-tsconfig.js
index fb48a43..de18175 100644
--- a/node_modules/@swc-node/register/lib/read-default-tsconfig.js
+++ b/node_modules/@swc-node/register/lib/read-default-tsconfig.js
@@ -139,6 +139,7 @@ function tsCompilerOptionsToSwcConfig(options, filename) {
                 useBuiltins: true,
             }
             : undefined,
+        baseUrl: path_1.resolve(options.baseUrl ?? './'),
         paths: Object.fromEntries(Object.entries((_h = options.paths) !== null && _h !== void 0 ? _h : {}).map(([aliasKey, aliasPaths]) => {
             var _a;
             return [
diff --git a/node_modules/@swc-node/register/lib/register.js b/node_modules/@swc-node/register/lib/register.js
index 7d4cfd8..51adf8a 100644
--- a/node_modules/@swc-node/register/lib/register.js
+++ b/node_modules/@swc-node/register/lib/register.js
@@ -88,7 +88,7 @@ function compile(sourcecode, filename, options, async = false) {
 exports.compile = compile;
 function register(options = {}, hookOpts = {}) {
     if (!process.env.SWCRC) {
-        options = (0, read_default_tsconfig_1.readDefaultTsConfig)();
+        options = Object.keys(options).length ? options : (0, read_default_tsconfig_1.readDefaultTsConfig)();
     }
     options.module = ts.ModuleKind.CommonJS;
     (0, sourcemap_support_1.installSourceMapSupport)();

[eliellis]

I have opened #725 to address this issue. @Brooooooklyn please take a look when you can.