Bison grammar import for analysis
ibex import bison converts Bison-shaped grammar structure into ordinary extended Ibex source for analysis. It is a one-way adapter, not a parser generator compatibility mode. Imported C actions remain opaque, are never executed by analysis, and make Ruby generation fail before code is emitted.
ibex import bison parser.y -o parser.analysis.y
ibex import bison --format=json parser.y > import-report.json
ibex explain --state=STATE parser.y
ibex metrics parser.yexplain, metrics, diff, and the other read-only grammar analysis paths recognize a file with two Bison %% section markers and import it in memory. Source-repair commands need a canonical imported file because edits against the generated analysis source do not map byte-for-byte onto the Bison input.
Conversion contract
| Classification | Directives | Treatment |
|---|---|---|
| converted | %token, %left, %right, %nonassoc, %precedence, %start, %expect, %expect-rr, %empty, %prec | existing extended declarations or production syntax |
| recognized metadata | %nterm, %type, %union, %destructor, %printer, %param, %parse-param, %lex-param, %define, %code | positioned report entries; no new Ibex syntax is invented |
| unsupported | %dprec, %merge, GLR controls, generator/output controls, and every unknown directive | every occurrence is reported with its original line and column |
$$, $1, $<type>1, and @$ become result, val[0], val[0], and result_loc inside an opaque hexadecimal action sentinel. Ordinary @1 locations remain @1. Balanced action scanning handles nested braces, strings, character literals, and C comments iteratively.
Bison permits uppercase nonterminals, lowercase terminals, names that collide after punctuation removal, and names that are Ibex declaration words. The adapter deterministically namespaces nonterminals as bison_nt_*, maps lowercase terminals into BISON_T_*, and adds stable numeric suffixes to sanitization collisions. Named LHS forms such as expression[result]: are recognized.
The source and JSON report distinguish general unsupported directives from structural gaps. Output/language controls and opaque initialization hooks do not make the recovered production graph incomplete. Unknown directives, %dprec, %merge, GLR semantics, and grammar-macro directives do. A generated header therefore contains exactly one of:
# ibex-bison-structural-status: complete
# ibex-bison-structural-status: incompleteibex fix refuses a structurally incomplete import. This prevents a repair from being called safe when the bounded comparison only covered an approximation of the source grammar.
Limits and failure behavior
The defaults are 20 MiB of input, 1,000,000 structural tokens, 50,000 rule groups, and 100,000 actions. Override them with --max-bytes, --max-tokens, --max-rules, and --max-actions; every value must be positive. Exhaustion produces a version-1 JSON envelope and exits 2. Successful import exits 0 even when unsupported directives are present, because the report—not silence—is the result. Invocation and malformed-input errors go to stderr and exit 1.
-o writes atomically, rejects an input/output alias, and refuses symlink targets or files with multiple hard links. Third-party grammar files are not packaged or committed.
External evidence and the parse.y boundary
The scheduled external gate downloads five checksum-pinned GNU Bison grammars listed in gallery/EXTERNAL.md. It validates the import report, parses the generated source, normalizes it, and builds an Ibex LALR automaton. Current aggregate evidence is:
| Grammar | Rule groups | Actions | Productions | Ibex states | Unresolved S/R |
|---|---|---|---|---|---|
| GNU Bison calc | 5 | 7 | 13 | 22 | 0 |
| jq | 29 | 167 | 167 | 311 | 408 |
| PHP | 177 | 552 | 635 | 1,203 | 0 |
| PostgreSQL | 795 | 2,436 | 3,640 | 6,942 | 0 |
CRuby Bison-era parse.y | 223 | 594 | 781 | 1,303 | 0 |
For the pinned Bison-era CRuby grammar, GNU Bison 3.8.2 and Ibex both recover 781 non-augmented productions and zero unresolved conflicts. Bison reports 1,304 states while Ibex reports 1,303. The one-state difference is explained by the acceptance convention: Bison shifts end-of-input into a separate accept state, while Ibex accepts from the completed augmented start item.
Current CRuby parse.y is an Lrama input, not raw GNU Bison input. The pinned current file imports 231 rule groups and 486 actions, but reports 22 structurally unsupported occurrences, including %rule grammar macros. The approximate automaton has 1,152 states and 27 unresolved S/R conflicts. Selecting state 413 keeps explain bounded and yields one nonunifying reachability witness for the 'rescue' modifier shift/reduce choice within 8 tokens and 10,000 configurations. That is useful diagnostic evidence about the recovered approximation, not a claim about CRuby's actual Lrama table. fix refuses this input because proposing a language-preserving repair across unexpanded %rule definitions would be unsound.
The external gate reads public grammar text and GNU Bison's black-box report only. It does not inspect Bison implementation source or generated C, and publishes only aggregate counts.