Have a way to manage XML Attribute in YAML pom

[ChtiDkois]

Some plugins have configuration with no other way than an XML Attribute, but there is no equivalent in YAML for this.

As example, this is a maven-antrun-plugin configuration :

            <plugin>
                <artifactId>maven-antrun-plugin</artifactId>
                <executions>
                    <execution>
                        <id>generate-surefire-workdir</id>
                        <phase>generate-test-sources</phase>
                        <configuration>
                            <!-- do not generate if tests are skipped -->
                            <skip>${maven.test.skip}</skip>
                            <target>
                                <mkdir dir="${basedir}/target/surefire-workdir" />
                            </target>
                        </configuration>
                        <goals>
                            <goal>run</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>

Here, the mkdir element contains a "dir" attribute that cannot be transform into element.
I haven't found a way in YAML to describe this behavior.

  - groupId: org.apache.maven.plugins
    artifactId: maven-antrun-plugin
    executions:
    - id: generate-surefire-workdir
      phase: generate-test-sources
      # Do not generate if tests are skipped
      configuration:
        skip: ${maven.test.skip}
        target:
          mkdir: {dir: '${basedir}/target/surefire-workdir'}
      goals: [run]

I tried several way to put the "dir" value, no success.

Maybe we could have something like

        target:
          mkdir: 
            attr : {dir: '${basedir}/target/surefire-workdir'}

to specify we want it as a XML attribute ?

[callmetango]

My 0,02€/$/...: I had a look at adding attributes when working on issue #62. When researching I found the YAML2 attributes draft which didn't convince me for its syntactical deviation from the rest of the language. My second look was at the Node Properties section of the YAML 1.2 language spec, especially the Node Anchors. Since node properties prefix the node they seem not applicable when adding attributes.

Thinking of attributes I think of special key-value mappings added to a node. So what I came up with was the following Variant 1 introducing a new global type !!attr:

# Explicitly typed attributes.
plainTagWithAttributes: 42
  !!attr id: the-answer
  !!attr name: the answer to life, the universe and everything
# Flow style
plainTagWithAttributes: !!attr [ id: the-answer, name: "... to life ..." ] 42

Variant 2 is using the yet to introduce global type !!attr and the !!value type for specifying default values for mappings as well which leads obviously to a more verbose result:

# Explicitly typed attributes
plainTagWithAttributes:
  = : 42
  !!attr id: the-answer
  !!attr name: the answer to life, the universe and everything
# Flow style
plainTagWithAttributes: { = : 42 !!attr [ id: the-answer, name: "... to life ..." ] }

Used with a !!map this could give results even acceptable by Maven pom.xml veterans:

# Explicitly typed attributes.
transformers:
  - !!attr implementation: "FooTransformer"
    mainClass: Xxxx
  - !!attr implementation: 'BarTransformer'
    resource: .groovy
# Flow style
transformers: [ {!!attr implementation: "FooTransformer",  mainClass: Xxxx}, {!!attr implementation: "BarTransformer"} resource: .groovy}} ]

Of course all of the above require changes either to the composer used by polyglot-yaml or worse to the SnakeYAML parser. A straight forward attempt to parse the above examples failed me since these are obviously not YAML conformant. Which doesn't mean we should give up here. ;-)

A possibility was to use the Low Level API of SnakeYAML to extend the parser and/or composer. What do you think?

[Tzrlk]

As much as I love the terseness of Variant 1, using the existing functionality in SnakeYAML is probably way easier and better in the long run. Since there's no !!attr type (according to the docs), treating any !!map that contains a !!value (=:) as all other entries being attributes would solve the issue. Sadly, this does mean that if you have a !!map with attributes, you'd need to declare the !!value as the content map.

plainTagWithAttributes:
  id: the-answer
  name: the answer to life, the universe and everything
  =: 42

mapWithAttributes:
  cool: false
  clear: maybe
  =:
    color: blue
    sadness: palpable

If they're going to implement the !!attr type some time soon, then Variant 2 becomes the obvious choice.

[Tzrlk]

Upon re-reading this, I realised that you couldn't use !!attr with list elements anyway, as

listWithAttributes:
  !!attr id: bad-touch
  - item1
  - item2

isn't syntactically correct. You'd be forced to use =: regardless, making it

listWithAttributes:
  !!attr id: bad-touch
  =:
    - item1
    - item2

or

listWithAttributes:
  !!attr id: bad-touch
  =: [ item1, item2 ]