Daniel Sun created GROOVY-12403:
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Summary: Restore groovysh embedding extension points
Key: GROOVY-12403
URL: https://issues.apache.org/jira/browse/GROOVY-12403
Project: Groovy
Issue Type: Improvement
Reporter: Daniel Sun
h3. Context
The Gremlin Console (Apache TinkerPop) embeds groovysh. In Groovy 4, a host
could install an {{ImportCustomizer}} and
{{ASTTransformationCustomizer(ThreadInterrupt)}} on Groovysh's
{{CompilerConfiguration}}, and extend the command set. The Groovy 5 rewrite
onto JLine 3 (GROOVY-8162) removed those seams.
Reported on the dev list:
[https://lists.apache.org/thread/c66x4p4mhvmk7dojhddywzsgr4gpngs5]
h3. What's missing
# *Compiler configuration.* {{GroovyEngine}} builds the shell as {{new
GroovyShell(classLoader, sharedData)}} with no configuration.
{{CompilerConfiguration.DEFAULT}} is immutable, so there is no back door.
Executing {{import}} statements works, but the engine records them as snippets
and re-prepends them on every evaluation — expensive when the host preloads
dozens of star / static-star imports.
# *Embedding hooks on Main.* The Map overload of {{Main.start}} only takes
binding variables. Terminal, registries, prompt, banner, result printing, and
error handling are hardcoded. Hosts copy roughly 230 lines of {{Main}} and
re-diff them against every Groovy release.
# *ExtraConsoleCommands visibility.* {{/clear}}, {{/pwd}}, {{/cd}}, the
POSIX-style commands, and {{/!}} live in a protected nested class. That
compiles from another package in Groovy, but not from Java or under
{{@CompileStatic}}.
# *Class loader access.* The engine class loader field is protected. A getter
avoids a subclass whose only job is to read it (Grape + {{ServiceLoader}}
plugin install).
h3. Direction
Keep the binding map as bindings only. Do *not* add magic keys — they collide
with user variables and are awkward from Java.
* {{GroovyEngine(CompilerConfiguration)}} and a protected {{createShell}}
override, so customizers apply at compile time instead of as snippets.
* {{GroovyshOptions}} plus {{Main.start(GroovyshOptions, ...)}} for extra
{{CommandRegistry}} instances, a prompt supplier, result and error handlers, a
banner toggle, and an optional {{Terminal}}.
* {{ExtraConsoleCommands}} as a public top-level class; keep
{{Main.ExtraConsoleCommands}} as a deprecated subclass for existing Groovy
callers.
* {{GroovyEngine.getClassLoader()}}.
Mark {{GroovyshOptions}} incubating so the shape can still settle after a first
embedder uses it.
h3. Example
{code:groovy}
def config = new CompilerConfiguration()
config.addCompilationCustomizers(
new ImportCustomizer().addStarImports('java.util.concurrent.atomic'),
new ASTTransformationCustomizer(ThreadInterrupt))
Main.start(GroovyshOptions.builder()
.compilerConfiguration(config)
.prompt { 'gremlin> ' }
.showBanner(false)
.build(), args)
{code}
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