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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