module: custom --conditions flag option

doc/api/cli.md

@@ -76,6 +76,21 @@ $ node --completion-bash > node_bash_completion
 $ source node_bash_completion
 ```
 
+### `-cc`, `--conditions=conditionA,conditionB`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+Enable experimental support for custom conditional exports resolution
+conditions.
+
+Any custom comma-separated string condition names are permitted.
+
+The default Node.js conditions of `"node"`, `"default"`, `"import"` and
+`"require"` will always apply as defined.
+
 ### `--cpu-prof`
 <!-- YAML
 added: v12.0.0

doc/node.1

@@ -78,6 +78,10 @@ Aborting instead of exiting causes a core file to be generated for analysis.
 .It Fl -completion-bash
 Print source-able bash completion script for Node.js.
 .
+.It Fl cc , Fl -conditions Ar string
+Use custom conditional exports conditions
+.Ar string
+.
 .It Fl -cpu-prof
 Start the V8 CPU profiler on start up, and write the CPU profile to disk
 before exit. If

lib/internal/modules/cjs/loader.js

@@ -85,6 +85,7 @@ const manifest = getOptionValue('--experimental-policy') ?
   require('internal/process/policy').manifest :
   null;
 const { compileFunction } = internalBinding('contextify');
+const userConditions = (getOptionValue('--conditions') || '').split(',');
 
 // Whether any user-provided CJS modules had been loaded (executed).
 // Used for internal assertions.
@@ -625,23 +626,14 @@ function resolveExportsTarget(baseUrl, target, subpath, mappingKey) {
           'contain numeric property keys.');
     }
     for (const p of keys) {
-      switch (p) {
-        case 'node':
-        case 'require':
-          try {
-            return resolveExportsTarget(baseUrl, target[p], subpath,
-                                        mappingKey);
-          } catch (e) {
-            if (e.code !== 'ERR_PACKAGE_PATH_NOT_EXPORTED') throw e;
-          }
-          break;
-        case 'default':
-          try {
-            return resolveExportsTarget(baseUrl, target.default, subpath,
-                                        mappingKey);
-          } catch (e) {
-            if (e.code !== 'ERR_PACKAGE_PATH_NOT_EXPORTED') throw e;
-          }
+      if (cjsConditions.has(p) || p === 'default') {
+        try {
+          return resolveExportsTarget(baseUrl, target[p], subpath,
+                                      mappingKey);
+        } catch (e) {
+          if (e.code !== 'ERR_PACKAGE_PATH_NOT_EXPORTED') throw e;
+        }
+        break;
       }
     }
     throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
@@ -1006,7 +998,7 @@ Module._load = function(request, parent, isMain) {
 };
 
 // TODO: Use this set when resolving pkg#exports conditions.
-const cjsConditions = new SafeSet(['require', 'node']);
+const cjsConditions = new SafeSet(['require', 'node', ...userConditions]);
 Module._resolveFilename = function(request, parent, isMain, options) {
   if (NativeModule.canBeRequiredByUsers(request)) {
     return request;

lib/internal/modules/esm/resolve.js

@@ -51,7 +51,8 @@ const {
 const { Module: CJSModule } = require('internal/modules/cjs/loader');
 
 const packageJsonReader = require('internal/modules/package_json_reader');
-const DEFAULT_CONDITIONS = ObjectFreeze(['node', 'import']);
+const userConditions = (getOptionValue('--conditions') || '').split(',');
+const DEFAULT_CONDITIONS = ObjectFreeze(['node', 'import', ...userConditions]);
 const DEFAULT_CONDITIONS_SET = new SafeSet(DEFAULT_CONDITIONS);
 
 

src/node_options.cc

@@ -281,6 +281,11 @@ DebugOptionsParser::DebugOptionsParser() {
 }
 
 EnvironmentOptionsParser::EnvironmentOptionsParser() {
+  AddOption("--conditions",
+            "set the conditional exports conditions",
+            &EnvironmentOptions::conditions,
+            kAllowedInEnvironment);
+  AddAlias("-cc", "--conditions");
   AddOption("--diagnostic-dir",
             "set dir for all output files"
             " (default: current working directory)",

src/node_options.h

@@ -100,6 +100,7 @@ class DebugOptions : public Options {
 class EnvironmentOptions : public Options {
  public:
   bool abort_on_uncaught_exception = false;
+  std::string conditions;
   bool enable_source_maps = false;
   bool experimental_json_modules = false;
   bool experimental_modules = false;

test/es-module/test-esm-custom-exports.mjs

@@ -0,0 +1,10 @@
+// Flags: --conditions=custom-condition,another
+import { mustCall } from '../common/index.mjs';
+import { strictEqual } from 'assert';
+import { requireFixture, importFixture } from '../fixtures/pkgexports.mjs';
+[requireFixture, importFixture].forEach((loadFixture) => {
+  loadFixture('pkgexports/condition')
+    .then(mustCall((actual) => {
+      strictEqual(actual.default, 'from custom condition');
+    }));
+});