Invalid instruction can use better error messaging

[jitsedesmet]

When the Java ByteCode contains an instruction that is invalid, the error message totally misses the point.

For example:

import java.lang.String;
import java.lang.System;
import java.io.PrintStream;
version 12;
public class MyClass {
    public static void main(final String[] args) {
        getstatic System#PrintStream out
        apples
        ldc "Hello World!"
        invokevirtual PrintStream#void println(String)
        return
    }
}

Results in a stack trace

Exception in thread "main" java.io.IOException: An exception occured while assembling HelloWorld.jbc
        at com.guardsquare.proguard.assembler.io.JbcReader.read(JbcReader.java:78)
        at proguard.io.FilteredDataEntryReader.read(FilteredDataEntryReader.java:85)
        at proguard.io.FilteredDataEntryReader.read(FilteredDataEntryReader.java:85)
        at proguard.io.FilteredDataEntryReader.read(FilteredDataEntryReader.java:85)
        at proguard.io.FileSource.pumpDataEntries(FileSource.java:71)
        at com.guardsquare.proguard.assembler.AssemblerCli.readInput(AssemblerCli.java:156)
        at com.guardsquare.proguard.assembler.AssemblerCli.main(AssemblerCli.java:79)
Caused by: com.guardsquare.proguard.assembler.ParseException: Line 9: An exception occured while parsing main(java.lang.String[])
        at com.guardsquare.proguard.assembler.InstructionsParser.visitProgramMethod(InstructionsParser.java:94)
        at proguard.classfile.ProgramMethod.accept(ProgramMethod.java:140)
        at com.guardsquare.proguard.assembler.ClassMembersParser.visitProgramMethod(ClassMembersParser.java:182)
        at proguard.classfile.ProgramMethod.accept(ProgramMethod.java:140)
        at com.guardsquare.proguard.assembler.ClassMembersParser.visitProgramClass(ClassMembersParser.java:102)
        at proguard.classfile.ProgramClass.accept(ProgramClass.java:544)
        at com.guardsquare.proguard.assembler.ClassParser.visitProgramClass(ClassParser.java:170)
        at proguard.classfile.ProgramClass.accept(ProgramClass.java:544)
        at com.guardsquare.proguard.assembler.io.JbcReader.read(JbcReader.java:69)
        ... 6 more
Caused by: com.guardsquare.proguard.assembler.ParseException: Line 9: Expected label colon ':' but got word.
        at com.guardsquare.proguard.assembler.Parser.expect(Parser.java:117)
        at com.guardsquare.proguard.assembler.Parser.expect(Parser.java:202)
        at com.guardsquare.proguard.assembler.InstructionsParser.visitCodeAttribute(InstructionsParser.java:220)
        at proguard.classfile.attribute.CodeAttribute.accept(CodeAttribute.java:138)
        at com.guardsquare.proguard.assembler.InstructionsParser.visitProgramMethod(InstructionsParser.java:84)
        ... 14 more

As can be seen, the error points to line 9 even though this is unrelated. The example here is clear, apples is clearly not a valid instruction, but a typo in an instruction like astore_0 is easier to be made.