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cex: always show ε/%empty in counterexamples

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On a case such as
    %%
    exp
    : empty "a"
    | "a" empty

    empty
    : %empty

we used to display

    warning: shift/reduce conflict on token "a" [-Wcounterexamples]
    Example: • "a"
    Shift derivation
      exp
      ↳ 2: • "a" empty
                 ↳ 2: ε
    Example: • "a"
    Reduce derivation
      exp
      ↳ 1: empty  "a"
           ↳ 3: •

where the shift derivation shows an item "2: empty → ε", with an
explicit "ε", but the reduce derivation shows "3: empty → •", without
"ε".

For consistency, let's always show ε/%empty in rules with an empty
rhs:

    Reduce derivation
      exp
      ↳ 1: empty    "a"
           ↳ 3: ε •

* src/derivation.c (derivation_width, derivation_print_tree_impl):
Always show ε/%empty in counterexamples.
* tests/diagnostics.at: Check that case.
* tests/conflicts.at, tests/counterexample.at: Adjust.
This commit is contained in:
Akim Demaille
2020-08-31 07:22:17 +02:00
parent 82d913741b
commit 325ec7d324
6 changed files with 141 additions and 66 deletions
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11
NEWS
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@@ -19,17 +19,18 @@ GNU Bison NEWS
*** Counterexamples
Counterexamples now show the rule numbers:
Counterexamples now show the rule numbers, and always show ε for rules
with an empty right-hand side. For instance
exp
↳ 1: "if" exp "then" exp
↳ 2: "if" exp "then" exp • "else" exp
↳ 1: e1 e2 "a"
↳ 3: ε • ↳ 1: ε
instead of
exp
↳ "if" exp "then" exp
↳ "if" exp "then" exp • "else" exp
↳ e1 e2 "a"
↳ • ↳ ε
* Noteworthy changes in release 3.7.1 (2020-08-02) [stable]