Strengthen shell directive validation (#5689) [ci fast]

Signed-off-by: Paolo Di Tommaso <paolo.ditommaso@gmail.com>

modules/nextflow/src/main/groovy/nextflow/processor/TaskConfig.groovy

@@ -380,14 +380,26 @@ class TaskConfig extends LazyMap implements Cloneable {
             return BashWrapperBuilder.BASH
 
         if( value instanceof List )
-            return (List)value
+            return validateShell(value as List)
 
         if( value instanceof CharSequence )
-            return [ value.toString() ]
+            return validateShell(List.of(value.toString()))
 
         throw new IllegalArgumentException("Not a valid `shell` configuration value: ${value}")
     }
 
+    protected List<String> validateShell(List<String> shell) {
+        for( String it : shell ) {
+            if( !it )
+                throw new IllegalArgumentException("Directive `process.shell` cannot contain empty values - offending value: ${shell}")
+            if( !it || it.contains('\n') || it.contains('\r') )
+                throw new IllegalArgumentException("Directive `process.shell` cannot contain new-line characters - offending value: ${shell}")
+            if( it.startsWith(' ') || it.endsWith(' '))
+                throw new IllegalArgumentException("Directive `process.shell` cannot contain leading or tralining blanks - offending value: ${shell}")
+        }
+        return shell
+    }
+
     Path getStoreDir() {
         def path = get('storeDir')
         if( !path )

modules/nextflow/src/test/groovy/nextflow/processor/TaskConfigTest.groovy

@@ -671,4 +671,28 @@ class TaskConfigTest extends Specification {
         def e = thrown(ProcessUnrecoverableException)
         e.message == "Directive 'resourceLimits.cpus' cannot be a negative value - offending value: -1"
     }
+
+    def 'should validate shell cli' () {
+        given:
+        def config = new TaskConfig([:])
+        when:
+        config.validateShell(['bash','this','that'])
+        then:
+        noExceptionThrown()
+
+        when:
+        config.validateShell([''])
+        then:
+        thrown(IllegalArgumentException)
+
+        when:
+        config.validateShell(['bash\nthis\nthat'])
+        then:
+        thrown(IllegalArgumentException)
+
+        when:
+        config.validateShell(['bash', ' -eu '])
+        then:
+        thrown(IllegalArgumentException)
+    }
 }