Linter Rules for Nextlfow is a collection of CodeNarc rules designed to lint Nextflow DSL scripts and spot potential problems before a workflow script is run.

Because Nextflow DSL2 is a Groovy DSL it is possible to parse it syntactically with a Groovy parser and inspect it's Abstract Syntax Tree using a Groovy static analysis tool (linter) like CodeNarc.

This means that we can create custom CodeNarc rules that inspect Nextflow scripts (or config files) to detect and report potential issues.

This repository is distributed under the terms of the Apache 2 license. Full details are in the LICENSE file.

To build this library you can use

./gradlew clean build

The resulting jar files will be found in healthomics-nextflow-rules/build/libs/ and ast-echo/build/libs

To run lint checks against Nextflow files you need to have access to the CodeNarc jar as well as an SLF4J implementation for logging.

To download CodeNarc along with its dependent Groovy libs

wget https://repo1.maven.org/maven2/org/codenarc/CodeNarc/3.3.0/CodeNarc-3.3.0-all.jar

Download SLF4J API and an implementation such as SLF4J simple.

wget https://repo1.maven.org/maven2/org/slf4j/slf4j-api/1.7.36/slf4j-api-1.7.36.jar
wget https://repo1.maven.org/maven2/org/slf4j/slf4j-simple/1.7.36/slf4j-simple-1.7.36.jar

You will also need an installation of Java (at least version 1.8 but 17 or higher is preferable). To test for the existence of Java you can run

java -version

If there is no java installation then using SDKMAN is one of the simpler options for installation that also supports having multiple versions if that is required.

Assuming your have built this library (see "Build" above) you can run the following command.

java  -Dorg.slf4j.simpleLogger.defaultLogLevel=error \
  -classpath ./linter-rules/build/libs/linter-rules-0.1.jar:CodeNarc-3.3.0-all.jar:slf4j-api-1.7.36.jar:slf4j-simple-1.7.36.jar \
  org.codenarc.CodeNarc \
  -report=text:stdout \
  -rulesetfiles=rulesets/healthomics.xml \
  -includes=**/**.nf

If your jar files are in different locations adjust the -classpath line as appropriate. All lines after org.codenarc.CodeNarc are CodeNarc command line parameters

Here we have configured CodeNarc to use the rules in rulesets/healthomics.xml which is defined in this library and contained in this libraries JAR file. The -includes parameter takes an Ant style pattern. This pattern will inspect all *.nf files at the current location and in subdirectories.

If you only wish to check general Nextflow lint rules and not include those specialized to AWS HealthOmics then you can run:

java  -Dorg.slf4j.simpleLogger.defaultLogLevel=error \
  -classpath ./linter-rules/build/libs/linter-rules-0.1.jar:CodeNarc-3.3.0-all.jar:slf4j-api-1.7.36.jar:slf4j-simple-1.7.36.jar \
  org.codenarc.CodeNarc \
  -report=text:stdout \
  -rulesetfiles=rulesets/general.xml \
  -includes=**/**.nf

A Dockerfile is provided for this project which will build an image that contains the scripts in scripts/ and the required JAR files. Recent copies of the container image are publically available from ECR Public Gallery.

If you prefer to build the container from source:

docker build -t linter-rules-for-nextflow .

The container is configured to (by default) run all rules herein against all Nextflow (*.nf) files found in the data volume. For example, to check the files in the examples/ folder:

cd examples
docker run -v $PWD:/data linter-rules-for-nextflow

which will produce a report similar to:

CodeNarc Report - Jan 11, 2024, 8:29:21?PM

Summary: TotalFiles=1 FilesWithViolations=1 P1=3 P2=0 P3=0

File: example.nf
    Violation: Rule=ContainerUriIsEcrUri P=1 Line=2 Msg=[The container image URI 'ubuntu:latest' does not match the pattern '\d{12}\.dkr\.ecr\..+\.amazonaws.com/.*'. Replace with an ECR image URI.] Src=[container 'ubuntu:latest']
    Violation: Rule=ContainerUriIsEcrUri P=1 Line=15 Msg=[The container image URI 'ubuntu:latest' does not match the pattern '\d{12}\.dkr\.ecr\..+\.amazonaws.com/.*'. Replace with an ECR image URI.] Src=[container 'ubuntu:latest']
    Violation: Rule=PublishDirRule P=1 Line=17 Msg=[AWS HealthOmics requires the value of publishDir to be '/mnt/workflow/pubdir'. Please replace the current value] Src=[publishDir '/foo']

[CodeNarc (https://codenarc.org) v3.3.0]
CodeNarc completed: (p1=3; p2=0; p3=0) 1757ms

If you only want to check the general rules using the container you can set the ruleset environment variable to general as follows:

cd examples
docker run -v $PWD:/data -e ruleset=general linter-rules-for-nextflow

The container also contains the ast-echo application along with a script to run it (echo-tree.sh). For example:

docker run -v $PWD/examples:/data linter-rules-for-nextflow ./echo-tree.sh /data/example.nf

We currently use Groovy 3.0.18 and Java 17 for development.

CodeNarc rules are typically implemented using the visitor pattern. Rules that follow this pattern will extend the org.codenarc.rule.AbstractAstVisitorRule and declare a "companion" visitor class that extends the org.codenarc.rule.AbstractAstVisitor. The AbstractAstVisitor defines several methods beginning with visit such as visitMethodCallExpression(MethodCallExpression expression). The visitor class associated with the rule will need to override the visit method (or methods) that are relevant to the code they wish to examine.

There is one visit method for each of the possible Groovy language expressions and statements. Unfortunately there are dozens of Groovy expressions and statements which can make it difficult to know which your rule needs to override. It is also not immediately obvious how Nextflow statements and expressions are semantically realized as Groovy. To help you decide, this package includes a Java application (AstEchoCli) that will echo the Groovy Abstract Syntax Tree for any Nextflow script or other valid Groovy or Groovy DSL. Consult the README.md in the ast-echo folder of this project for build and usage instructions.

New rules should be added to the appropriate package in ./linter-rules/src/groovy.

A rule consists of a Rule and an ASTVisitor typically in the same groovy file. The Rule class should extend AbstractAstVisitorRule

class MyRule extends AbstractAstVisitorRule {

    String name = 'MyRule'
    int priority = 3        // priority indicates severity of the violation. 1 = severe, 2 = moderate, 3 = advisory
    Class astVisitorClass = MyRuleAstVisitor
}

class MyRuleAstVisitor extends AbstractAstVisitor {
    // override visitor methods as needed
    // for example:

    @Override
    void visitMethodCallExpression(MethodCallExpression expression){
        // code here to inspect the expression to determine if it is relevant to the check and if it violates the check
        
        // for any violations, add them
        if(somethingBad){
            addViolation(expression, "message explaining violation and potential fix")
        }
        
        // importantly, call the super method to continue traversal of the AST before you exit the method
        super.visitMethodCallExpression(expression)
    }
}

All rules should include tests for cases that produce no violations and cases that should produce violations. Tests should extend AbstractRuleTestCase<T> where T is the class of your new rule.

For example:

class CpuRuleTest extends AbstractRuleTestCase<CpuRule> {

    // provides an instance of the rule to the test
    @Override
    protected CpuRule createRule() {
        new CpuRule()
    }

    // test the properties of the rule are what you think they should be
    @Test
    void ruleProperties() {
        assert rule.priority == 2
        assert rule.name == "CpuRule"
    }

    // provide one or more tests that produce no violations for valid code (and edge cases)
    @Test
    void cpuRule_NoViolationsMin() {
        final SOURCE =
                '''
                process MY_PROCESS {
                 cpus 2
                }
                '''
        assertNoViolations(SOURCE)
    }

    // provide at least one test that contains source that will trigger one or more violations
    @Test
    void cpuRule_TooManyArgsViolation() {
        final SOURCE =
                '''
                process MY_PROCESS {
                    cpus 14, 18
                }
                '''
        // assertion that only one violation occurs and that it matches the expected priority, violating code fragment
        // and violation message.
        // several other assert violation methods are available for various scenarios
        assertSingleViolation(SOURCE, 3, "cpus 14, 18",
                "the cpus directive must have only one argument")
    }
}

To run all tests in this project you should use:

./gradlew test

To run all tests in a specific Rule test class (in this case CpuRuleTest):

./gradlew test --tests CpuRuleTest

To run a specific test method in a test class:

./gradlew test --tests CpuRuleTest.cpuRule_TooManyArgsViolation

When a rule is created it should be added to the linter-rules/src/resources/rulesets/healthomics.xml file. If the rule is general to any Nextflow environment then it should also be added to the linter-rules/src/resources/rulesets/general.xml Entries use the fully qualified class name of the rule. Assuming the new Rule is called NewRule and the package is software.amazon.nextflow.rules.healthomics, the rule to be added will be:

<rule class="software.amazon.nextflow.rules.healthomics.NewRule"/>