Add variable NXF_CONFIG_FILE

modules/nextflow/src/main/groovy/nextflow/config/ConfigBuilder.groovy

@@ -77,6 +77,8 @@ class ConfigBuilder {
 
     Map<ConfigObject, String> emptyVariables = new LinkedHashMap<>(10)
 
+    Map<String,String> env = new HashMap<>(System.getenv())
+
     List<String> warnings = new ArrayList<>(10);
 
     {
@@ -205,6 +207,7 @@ class ConfigBuilder {
 
         /**
          * Config file in the pipeline base dir
+         * This config file name should be predictable, therefore cannot be overridden
          */
         def base = null
         if( baseDir && baseDir != currentDir ) {
@@ -217,8 +220,10 @@ class ConfigBuilder {
 
         /**
          * Local or user provided file
+         * Default config file name can be overridden with `NXF_CONFIG_FILE` env variable
          */
-        def local = currentDir.resolve('nextflow.config')
+        def configFileName = env.get('NXF_CONFIG_FILE') ?: 'nextflow.config'
+        def local = currentDir.resolve(configFileName)
         if( local.exists() && local != base ) {
             log.debug "Found config local: $local"
             result << local

modules/nextflow/src/test/groovy/nextflow/config/ConfigBuilderTest.groovy

@@ -280,6 +280,45 @@ class ConfigBuilderTest extends Specification {
         folder?.deleteDir()
     }
 
+
+    def 'should fetch the config path from env var' () {
+        given:
+        def folder = File.createTempDir()
+        def configMain = new File(folder,'my.config').absoluteFile
+
+
+        configMain.text = """
+        process.name = 'alpha'
+        params.one = 'a'
+        params.two = 'b'
+        """
+
+        // relative path to current dir
+        when:
+        def config = new ConfigBuilder(env: [NXF_CONFIG_FILE: 'my.config']) .setCurrentDir(folder.toPath()) .build()
+        then:
+        config.params.one == 'a'
+        config.params.two == 'b'
+        config.process.name == 'alpha'
+
+        // absolute path
+        when:
+        config = new ConfigBuilder(env: [NXF_CONFIG_FILE: configMain.toString()]) .build()
+        then:
+        config.params.one == 'a'
+        config.params.two == 'b'
+        config.process.name == 'alpha'
+
+        // default should not find it
+        when:
+        config = new ConfigBuilder() .build()
+        then:
+        config.params == [:]
+
+        cleanup:
+        folder?.deleteDir()
+    }
+
     def 'CLI params should overrides the ones in one or more profiles' () {
 
         setup: