Lukasz Lenart created WW-5767:
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Summary: Apply value substitution to scoped-constant values, as
for constant
Key: WW-5767
URL: https://issues.apache.org/jira/browse/WW-5767
Project: Struts 2
Issue Type: Improvement
Components: XML Configuration
Reporter: Lukasz Lenart
h2. Background
[WW-3476|https://issues.apache.org/jira/browse/WW-3476] adds the
{{scoped-constant}} element to {{package}} (struts-7.5.dtd). Its values are
stored exactly as written: {{XmlDocConfigurationProvider.loadScopedConstants}}
passes the raw {{value}} attribute to
{{PackageConfig.Builder.addScopedConstant}}.
The global {{constant}} element is different. Since 2.5.6 its value goes
through the injected {{ValueSubstitutor}} (default {{EnvsValueSubstitutor}}) in
{{XmlDocConfigurationProvider}} before it is registered, which resolves
environment variables and system properties once, at load time:
{code:xml}<constant name="some.constant" value="${env.SOME_VALUE}"/>
{code}
The same expression in a scoped constant is kept literally:
{code:xml}<package name="admin" extends="struts-default">
<scoped-constant name="some.scopable.constant" value="${env.SOME_VALUE}"/>
</package>
{code}
h2. Why this looks unintended
The WW-3476 design ruled out per-request expression evaluation of scoped
constants, because their values are static. Value substitution is something
else: it runs once while the configuration loads and produces a static string,
exactly like for {{constant}}. Leaving it out makes the two elements behave
differently for no design reason.
h2. Proposal
* In {{XmlDocConfigurationProvider.loadScopedConstants}}, run the value through
{{valueSubstitutor}} when one is set, the same way global constants are handled.
* No change to {{PackageConfig}}, the startup validation or
{{ScopedConstantProvider}}. They receive the substituted string.
h2. Tests
* {{XmlConfigurationProviderPackagesTest}}: a fixture with a scoped constant
whose value refers to a system property set by the test resolves to the
property's value.
* A literal value without an expression is kept unchanged.
h2. Documentation
The struts-site page {{core-developers/package-configuration.md}} currently
says value substitution is not supported for scoped constants
([apache/struts-site#351|https://github.com/apache/struts-site/pull/351]).
Update that sentence once this lands.
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