Use Locale.ROOT for toLowerCase/toUpperCase calls

[AlexProgrammerDE]

Summary

• Replaced all bare toLowerCase() and toUpperCase() calls with toLowerCase(Locale.ROOT) / toUpperCase(Locale.ROOT) across Serializers.java, RootSerializer.java, and SerializersTest.java.

Why This Is Needed

Java's String.toLowerCase() and String.toUpperCase() without a Locale argument use Locale.getDefault(), which is derived from the system/JVM locale. This means the same code can produce different results on different machines depending on the OS locale settings.

The most well-known problem is with the Turkish locale (tr_TR), where:

Expression	Locale.ENGLISH / Locale.ROOT	Locale("tr", "TR")
"INTEGER".toLowerCase()	"integer"	"ınteger" (dotless ı)
"integer".toUpperCase()	"INTEGER"	"İNTEGER" (dotted İ)
"I".toLowerCase()	"i"	"ı"
"i".toUpperCase()	"I"	"İ"

Concrete impact in this codebase

• Serializers.java: The error message includes sourceTypeName.toLowerCase() (e.g., turning "Boolean" into "boolean" for the phrase "boolean-to-string coercion"). On a Turkish-locale system, "Boolean" would become "boolean" correctly, but type names containing I (like "BigInteger") would become "bıgınteger" — a garbled error message.

• RootSerializer.java: Environment variable names are uppercased with toUpperCase(). On a Turkish-locale system, a key containing "i" would be converted to "İ" (with a dot above) instead of "I", causing environment variable lookups to silently fail to match the actual env var.

Examples of real-world breakage

// On a Turkish-locale JVM:
"myAppConfig_item".toUpperCase()
// Expected: "MYAPPCONFIG_ITEM"
// Actual:   "MYAPPCONFIG_İTEM"  ← env var lookup will fail!

"Integer".toLowerCase()
// Expected: "integer"
// Actual:   "ınteger"  ← broken error message

Locale.ROOT is the correct choice here (rather than Locale.ENGLISH) because these are programmatic/technical strings, not user-facing text that needs language-specific rules. Locale.ROOT provides locale-independent behavior, which is exactly what's needed for identifiers, env var names, and type names.

Test plan

• Verified no remaining bare toLowerCase()/toUpperCase() calls in the codebase
• Existing tests should continue to pass since behavior is unchanged on non-Turkish locales

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR makes string case conversions locale-independent by updating toLowerCase()/toUpperCase() calls to use Locale.ROOT, preventing behavior differences under non-English default JVM locales (e.g., Turkish) in serializer error messages and environment variable resolution.

Changes:

• Updated serializer exception message formatting to use toLowerCase(Locale.ROOT).
• Updated environment variable key normalization to use toUpperCase(Locale.ROOT).
• Updated related test helper message formatting to match production behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
configlib-core/src/main/java/de/exlll/configlib/Serializers.java	Uses toLowerCase(Locale.ROOT) when building coercion-related exception messages.
configlib-core/src/main/java/de/exlll/configlib/RootSerializer.java	Uses toUpperCase(Locale.ROOT) when normalizing env var keys for lookups.
configlib-core/src/test/java/de/exlll/configlib/SerializersTest.java	Aligns expected exception message formatting with Locale.ROOT lowercasing.

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[Exlll]

Hi @AlexProgrammerDE, thanks your for contribution. 👍

Changing the locale looks like a breaking change to me which I why I will not accept this PR as is. The correct, non-breaking way to implement this is to make the locale configurable via ConfigurationProperties. Are you interested in implementing it this way? Also, please base your PR on the dev branch and not on master.

[AlexProgrammerDE]

Hi, I don't think this can break any major code. This simply updates exception messages to look correct and also fixes environment variables for turkish minecraft servers. Who would want environment variables to work on english servers but fail to apply on turkish servers?

[Exlll]

Yeah, you are probably (and hopefully) right. I just tested to set İNTEGER as an environment variable and it isn't even a valid name on Linux (can't test Windows).

[AlexProgrammerDE]

Thank you! <3

[Exlll]

I've released version 4.8.1. Thanks again for the contribution!