feat!: remove the constraint on packages exports default must be the last one (#171)

closes #160

The spec never mentioned the logic where "default" must be last or it should throw an error.

https://nodejs.org/api/esm.html#resolution-and-loading-algorithm

`enhanced-resolve` took the meaning from https://nodejs.org/docs/v20.13.1/api/packages.html#conditional-exports

"This condition should always come last."

This statement is not part of the specification, it is a recommendation.

Author: Boshen

src/lib.rs

@@ -1512,19 +1512,9 @@ impl<Fs: FileSystem> ResolverGeneric<Fs> {
             JSONValue::Object(target) => {
                 // 1. If exports contains any index property keys, as defined in ECMA-262 6.1.7 Array Index, throw an Invalid Package Configuration error.
                 // 2. For each property p of target, in object insertion order as,
-                for (i, (key, target_value)) in target.iter().enumerate() {
-                    // https://nodejs.org/api/packages.html#conditional-exports
-                    // "default" - the generic fallback that always matches. Can be a CommonJS or ES module file. This condition should always come last.
-                    // Note: node.js does not throw this but enhanced-resolve does.
-                    let is_default = key == "default";
-                    if i < target.len() - 1 && is_default {
-                        return Err(ResolveError::InvalidPackageConfigDefault(
-                            package_url.join("package.json"),
-                        ));
-                    }
-
+                for (key, target_value) in target {
                     // 1. If p equals "default" or conditions contains an entry for p, then
-                    if is_default || conditions.contains(key) {
+                    if key == "default" || conditions.contains(key) {
                         // 1. Let targetValue be the value of the p property in target.
                         // 2. Let resolved be the result of PACKAGE_TARGET_RESOLVE( packageURL, targetValue, patternMatch, isImports, conditions).
                         let resolved = self.package_target_resolve(

src/tests/exports_field.rs

@@ -814,7 +814,7 @@ fn test_cases() {
         },
         TestCase {
             name: "Direct mapping #7",
-            expect: None,
+            expect: Some(vec!["./src/index.js"]), // `enhanced_resolve` is `None`
             exports_field: exports_field(json!({
                 ".": {
                     "default": "./src/index.js",

src/tests/imports_field.rs

@@ -507,7 +507,7 @@ fn test_cases() {
         },
         TestCase {
             name: "Direct mapping #7",
-            expect: None,
+            expect: Some(vec!["./src/index.js"]), // `enhanced_resolve` is `None`
             imports_field: imports_field(json!({
               "#a": {
                 "default": "./src/index.js",