Thanks @kaby76 for the report!
Please make sure that isn't already fixed in #319, and released with BNFC 2.9.0.

Should this not be fixed, please provide a MWE in form of a small .cf file that allow me to easily reproduce the bug.

It is not fixed in v2.9.0, at least not completely. STRINGTEXT : ~["\\] -> more; is fine, but CHARANY : ~[\'\\] -> more, mode(CHAREND); is not.

Here is how to reproduce it from a Bash shell. I assume that you have Git, downloaded antlr-4.9-complete.jar (see https://www.antlr.org/download/index.html), downloaded Java (I have jdk-11.0.4), and placed the Java executable on path for your OS.

mkdir temp
cd temp
git clone https://github.com/BNFC/bnfc.git --branch v2.9.0 --single-branch
cd bnfc/source/src
cp ../BNFC.cf .
# I assume you are using bnfc 2.9.0 executable--I'm using that for Windows.
bnfc --java-antlr --force BNFC.cf
cd bnfc
# I assume you have downloaded the latest Antlr jar and java on path.
java -jar ~/Downloads/antlr-4.9-complete.jar *.g4

The output of this is:

warning(156): bnfcLexer.g4:78:16: invalid escape sequence \'
Exception in thread "main" java.lang.RuntimeException: set is empty
    at org.antlr.v4.runtime.misc.IntervalSet.getMaxElement(IntervalSet.java:421)
    at org.antlr.v4.runtime.atn.ATNSerializer.serialize(ATNSerializer.java:169)
    at org.antlr.v4.runtime.atn.ATNSerializer.getSerialized(ATNSerializer.java:601)
    at org.antlr.v4.Tool.generateInterpreterData(Tool.java:745)
    at org.antlr.v4.Tool.processNonCombinedGrammar(Tool.java:400)
    at org.antlr.v4.Tool.process(Tool.java:369)
    at org.antlr.v4.Tool.processGrammarsOnCommandLine(Tool.java:328)
    at org.antlr.v4.Tool.main(Tool.java:172)

Ok, this seems to be a problem with more recent ANTLR versions, it is still ok with 4.5:

$ java  org.antlr.v4.Tool 
ANTLR Parser Generator  Version 4.5.1
...
$ java  org.antlr.v4.Tool -lib bnfc -package bnfc bnfc/bnfcLexer.g4
$ java  org.antlr.v4.Tool -lib bnfc -package bnfc bnfc/bnfcParser.g4

Ok, thanks. That kind of sucks. I'll check out Antlr's source and see what got messed up.

It seems like BNFC is still not implementing the escaping correctly, see the rules at: https://github.com/antlr/antlr4/blob/master/doc/lexer-rules.md
According to these rules, a single quote should not be escaped inside brackets (char sets).

CHARANY : ~[\'\\] -> more, mode(CHAREND);

This is wrong.

I suppose ANTLR got stricter checking the rules.

I think it's a regression in the Antlr rules. This stuff was moved into lexer modes, which broke things. My first test using EscAny without modes works fine with [\'foobar], but I'm adding in the rules one by one to figure what broke the grammar. In any case, you might want to generate the single-quote without a backslash.

There are at least two Git issues raised and then closed on escaped characters in Antlr: antlr/antlr4#1537 antlr/antlr4#1871 . For [\'], the tool gives a warning that it's not valid, but it crashes, which it shouldn't do. It is, apparently, now an invalid escape character, at least in character sets (https://github.com/antlr/antlr4/blob/master/doc/lexer-rules.md#lexer-rule-elements).

I am fixing the spurious escaping of 's in the ANTLR backend, but I agree that ANTLR should not crash on spurious escaping, just ignore it.

For [\'], the tool gives a warning that it's not valid, but it crashes, which it shouldn't do.

I left a comment at antlr/antlr4#1537: antlr/antlr4#1537 (comment)

I also filed antlr/antlr4#3024.

Did the fix work for you, @kaby76 ?

Yes, that fixed the problem. Thank you. It took me a while to get a build working because I work mostly on Windows in a MINGW64 environment. I could not get the build to work via Cabal (https://github.com/BNFC/bnfc#installing-the-development-version), but stack install --stack-yaml stack-8.10.3.yaml worked fine. I was looking to see what you have for nightly builds in order to set up a Windows env for building, but you're using Github Actions only on Linux. And, you have a .travis.yml file, which looks unused, and no Appveyor file.

I was looking to see what you have for nightly builds in order to set up a Windows env for building, but you're using Github Actions only on Linux.

PRs welcome!
The current GHA workflows are automatically generated by Haskell-CI, which does not add macOS or Windows builds. These could be added manually in a separate .yaml file, similar to https://github.com/agda/agda/blob/master/.github/workflows/nightly.yml maybe.

And, you have a .travis.yml file, which looks unused, and no Appveyor file.

I used to do CI on travis, but am migrating to Github Actions because of the new limitations for OSS builds by travis-ci.