firrtlCrossModule.antlr4Path java.util.NoSuchElementException: empty.head

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Checklist

• Did you specify the current behavior?
• Did you specify the expected behavior?
• Did you provide a code example showing the problem?
• Did you describe your environment?
• Did you specify relevant external information?

What is the current behavior?

build with error firrtlCrossModule.antlr4Path java.util.NoSuchElementException: empty.head

error massage:

[23/376] foreign-modules.dependencies.firrtl.build.firrtlCrossModule.antlr4Path 
1 targets failed
firrtlCrossModule.antlr4Path java.util.NoSuchElementException: empty.head
    scala.collection.immutable.Vector.head(Vector.scala:279)
    ammonite.$file.dependencies.firrtl.build$firrtlCrossModule.$anonfun$antlr4Path$4(build.sc:108)
    scala.collection.immutable.List.flatMap(List.scala:293)
    scala.collection.immutable.List.flatMap(List.scala:79)
    ammonite.$file.dependencies.firrtl.build$firrtlCrossModule.$anonfun$antlr4Path$3(build.sc:106)

What is the expected behavior?

Build without error.

Steps to Reproduce

1. install antlr:2 and antlr:4 on gentoo
2. clone https://github.com/chipsalliance/playground
3. run mill sanitytests.rocketchip

After a while, the following error will appear firrtlCrossModule.antlr4Path java.util.NoSuchElementException: empty.head

After careful analysis, I found that the version information of antlr2 is printed on stderr, which will cause os.proc(f).call(check = false).out.lines.head.split(" ").last fails because the lines are empty.

I will submit a patch to fix this issue later.

Your environment

• Chisel Verions: 3.5.4
• OS: Linux t480 6.1.12-gentoo-x86_64 #1 SMP PREEMPT_DYNAMIC Sat Feb 18 15:07:52 CST 2023 x86_64 Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz GenuineIntel GNU/Linux
• Verilator version: 5.006

External Information

None