Fix parser shift/reduce conflicts #4178
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Signed-off-by: Alexandre Terrasa <alexandre.terrasa@shopify.com>
Signed-off-by: Alexandre Terrasa <alexandre.terrasa@shopify.com>
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Motivation
I introduced shift/reduce conflicts in the grammar while adding support for begin-less ranges with
..and...(#3313). This PR fixes them.Example when compiling the parser before this PR:
The approach is the same as the one used by Whitequark (https://github.com/whitequark/parser/blob/de619a2ff36a39b4d43efa9b86cdec98621ed435/lib/parser/lexer.rl#L2026-L2035): duplicating the tokens
tDOT2andtDOT3and lexing them differently depending on the Ruby version used.One quirk with this approach is the way we display the parsing errors. Without any additional change, the error message would be:
In order to get a friendlier output, I tweaker the error generation method (see second commit) so we get back to the expected following error:
Compiling the parser after this PR:
No more shift/reduce conflict warning. 🎉
Test plan
See included automated tests.