[qodelicious]

In an ERE a quantifier needs something before it to repeat. GNU sed rejects *, +, ? and {m,n} at the start of the regex or right after (, |, ^ or $ with "Invalid preceding regular expression".

On main most of these already failed, but with a raw regex crate error (invalid regex '*': regex parse error ... repetition operator missing expression), and ^*, $* and a^* were accepted and matched. Now the regex parser tracks whether the last token can be repeated and reports GNU's message. Like GNU it reports once the whole regex has been read, so the column matches GNU's char number for addresses (/*/p gives 1:3, /a|*b/p gives 1:6, /^*/p gives 1:4). BRE is unchanged since a leading * is literal there.

Escaped characters, bracket expressions, groups and other quantifiers still count as something to repeat, so a**, a+?, ()*, (a|)*, [a]*, a{1}*, \(* and \** work as before. I checked every case in the tests against GNU sed 4.9.

Added test_ere_quantifier_without_preceding_atom and test_ere_quantifier_after_atom. The first fails on main. cargo test, cargo fmt --check and cargo clippy --all-targets --all-features -D warnings pass.

Fixes #290

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.07%. Comparing base (caef481) to head (d0e59da).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #616      +/-   ##
==========================================
+ Coverage   94.93%   95.07%   +0.13%     
==========================================
  Files          14       14              
  Lines        7292     7436     +144     
  Branches      434      439       +5     
==========================================
+ Hits         6923     7070     +147     
+ Misses        368      365       -3     
  Partials        1        1              

Flag	Coverage Δ
macos_latest	96.58% <100.00%> (+0.11%)	⬆️
ubuntu_latest	96.51% <100.00%> (+0.11%)	⬆️
windows_latest	0.00% <0.00%> (ø)

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[sylvestre]

please add a s case too, e.g. s/*/x/, it goes through the same parser

[qodelicious]

Added s//x/, s/a|+b/x/ and s/^/x/g. They all get the same error now.

[sylvestre]

Thanks for your PR