Versioning Behavior in DataWeave
New minor versions of DataWeave can introduce changes that modify the way the language behaves. You can use DataWeave system properties that behave as compatibility flags to continue using existing scripts that depend on the previous behavior. However, each flag defines a deletion version, which identifies the version in which the flag is no longer available and the behavior that it controls defaults to the changed behavior.
Specifying a DataWeave language level indicates to the DataWeave runtime what compatibility flags are available. To upgrade and maintain backward compatibility, you can set the language level of a previous version so that the flags available on that version remain visible even if they expire in the DataWeave version to which you upgrade. The language level defaults to the running DataWeave version and has to be at most the same as the runtime version.
For Mule applications, the language level is determined by the application’s minMuleVersion setting (see Feature Flags Reference in the Mule documentation). Given the minMuleVersion, the language level is computed by subtracting two major versions, as the following table shows:
| minMuleVersion | Language Level |
|---|---|
4.8 |
2.8 |
4.7 |
2.7 |
4.6 |
2.6 |
4.5 |
2.5 |
4.4 |
2.4 |
4.3 |
2.3 |
Setting the Mule version configures the application to use the corresponding DataWeave language level. This setting is independent of the DataWeave syntax version, which is set through a DataWeave script’s %dw directive. For details, see DataWeave Header.
For example, the com.mulesoft.dw.xml_reader.honourMixedContentStructure system property is a compatibility flag for language level 2.4, when it was introduced, and it is removed in DataWeave 2.6. In DataWeave 2.6, the property is visible only if you set the language level to 2.4 or 2.5. If you choose language level 2.4 it defaults to the old behavior, if you choose language level 2.5 it defaults to the new behavior.