fix(pathmap): leave the URL unchanged when a script mapping has no engine

[marevol]

Problem

Found while verifying the 15.8 → 15.9 upgrade path. On an installation upgraded without fess-script-groovy, a path mapping with a Groovy replacement such as

groovy:"http://mapped.invalid/en-${matcher.group(1)}"

maps nothing, and the log says something else happened:

WARN  No script engine is registered for groovy, so "groovy:..." is used as a plain replacement. Install the plugin providing it, such as fess-script-groovy for groovy.
WARN  Failed to apply http://example.com/docs/en/(.*) to http://example.com/docs/en/intro.html.
java.lang.IllegalArgumentException: named capturing group is missing trailing '}'

When the engine is missing, PathMappingHelper#resolveEngineMatcher falls back to m.replaceAll(replacement). Matcher#replaceAll reads its argument as a regular-expression replacement, so the ${...} of a GString is taken as a named-group reference and the call throws. PathMapping#process catches the exception, logs it with its stack trace and returns the URL unchanged, and it does so on every call: once per matching search result for a display mapping, and once per matching document for a crawl-time one. The "plain replacement" the first warning announces never happens.

Intended behaviour of the fallback

Group references in that fallback are intended, but not for scripts:

• 15.8.0 sent every replacement except a groovy: one through Matcher#replaceAll, and pathmap-guide.rst describes a replacement whose prefix is not a registered engine (https://…) as a plain regular-expression replacement. $1 has always worked there.
• In 15.8.0 a groovy: replacement was always evaluated as a script and never went through replaceAll. Falling back to a plain replacement when its engine is missing is new in 15.9 (feat(script)!: default to JavaScript and treat an unset script type as Groovy #3345).

Change

• If a replacement's prefix is in SCRIPT_ENGINE_NAMES (groovy, javascript) and that engine is not registered, the mapping is not applied: its matcher function returns the URL unchanged. The warning is still logged once per mapping, and now says the mapping is not applied.
• Every other prefix still goes through Matcher#replaceAll, $1 included.

The other option was to insert the script literally. That also stops the exception, but every matching URL would become the script text, and a crawl-time mapping would index documents under it. Leaving the URL alone is where 15.9 already ends up after the exception, just without a stack trace per URL. It is also how a document boost rule behaves without its engine: it boosts nothing (#3412). Installing fess-script-groovy makes such a mapping work as it did in 15.8.

Compatibility

test_replaceUrl_missingGroovyEngineIsPlainReplacement pinned the old result for groovy:url without an engine (groovy:urla.html). It is renamed to test_replaceUrl_missingGroovyEngineLeavesUrlUnchanged and now expects the URL unchanged. Mappings whose prefix is not groovy: or javascript: behave exactly as before.

Verification

New tests in PathMappingHelperTest:

• test_createPathMatcher_missingGroovyEngineDoesNotThrowOnScript: builds the matcher for groovy:"http://mapped.invalid/en-${matcher.group(1)}" with no Groovy engine and applies it. On main this throws IllegalArgumentException: named capturing group is missing trailing '}'; with this change it returns the URL.
• test_replaceUrl_missingGroovyEngineScriptLeavesUrlAndLogsNoFailure: runs two URLs through replaceUrl. Both come back unchanged, PathMapping logs no warning, and PathMappingHelper logs exactly one, naming fess-script-groovy. On main it fails on the Failed to apply … IllegalArgumentException warnings.
• test_replaceUrl_unregisteredPrefixKeepsGroupReferences: https://files.example.com/$1 still substitutes the group. It passes before and after and guards the intended behaviour.

mvn test -Dtest=PathMappingHelperTest: 40 tests. On main 1 failure and 1 error (the two new tests); on this branch 0 failures and 0 errors.

mvn test: 7490 tests, 0 failures, 0 errors.