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(fix): Debugger Classpath Loading and Initialization Order #927

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(fix): Debugger Classpath Loading and Initialization Order #927

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16 changes: 9 additions & 7 deletions modules/core/src/main/scala/ch/epfl/scala/debugadapter/internal/DebugTools.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -44,13 +44,7 @@ object DebugTools {
loadExpressionCompilers(debuggee, resolver, logger)
}

val decoder =
if (debuggee.scalaVersion.isScala3) {
TimeUtils.logTime(logger, "Loaded step filter") {
loadDecoder(debuggee.scalaVersion, resolver, logger)
}
} else None

// Load sourceLookUp first - this reads all class files from the classpath
val sourceLookUp = TimeUtils.logTime(logger, "Loaded all sources and classes") {
val classEntries = debuggee.classEntries
val distinctEntries = classEntries
Expand All @@ -63,6 +57,14 @@ object DebugTools {
SourceLookUpProvider(distinctEntries, logger)
}

// Load decoder after sourceLookUp - the decoder can reuse cached class data
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Copilot AI Jan 12, 2026

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The comment states "the decoder can reuse cached class data" but this appears to be inaccurate. The decoder (Scala3Decoder) creates its own classloader and reads from debuggee.classPath independently (see Scala3DecoderBridge line 46). There's no evidence of data sharing or cache reuse between sourceLookUp and the decoder. Consider revising this comment to more accurately describe the reason for this initialization order, such as "ensures all class entries are processed before decoder initialization" or similar.

Suggested change
// Load decoder after sourceLookUp - the decoder can reuse cached class data
// Load decoder after sourceLookUp to ensure all class entries are processed first

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val decoder =
if (debuggee.scalaVersion.isScala3) {
TimeUtils.logTime(logger, "Loaded step filter") {
loadDecoder(debuggee.scalaVersion, resolver, logger)
}
} else None

new DebugTools(allCompilers, decoder, sourceLookUp)
}

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