Print readable error messages in doc code blocks#2803
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Exercises six Lexer.Error variants triggered from inside {@ocaml[...]}
blocks. The expected .err files capture the current behaviour: the
catch-all branch at lib/Fmt_ast.ml stringifies the exception as
"invalid code block: Ocamlformat_parser_extended.Lexer.Error(_, _)",
which is unreadable. The next commit replaces these with human-readable
messages, and this test pins the change.
When parsing fails inside a `{@ocaml[...]}` block, the catch-all branch
formatted the exception with `Exn.pp`, which for `Lexer.Error` produced
the raw constructor pattern
`Ocamlformat_parser_extended.Lexer.Error(_, _)`. `Lexer.Error` (and most
other compiler-libs exceptions) register a printer via
`Location.register_error_of_exn`, but that table is separate from the
`Printexc` table `Exn.pp` consults, so the printer was never used.
Route the catch-all through `Location.error_of_exn` instead: if a
printer is registered, format its `main` message; otherwise fall back to
`Exn.pp`. This handles `Lexer.Error` and any other registered exception
(e.g. parser internals) without per-variant enumeration.
The .err diff against the previous commit shows the before/after for the
six variants the regression test exercises.
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Summary
{@ocaml[...]}block, the catch-all branch inFmt_ast.mlformatted the exception withExn.pp, which forLexer.Errorproduced the raw constructor patternOcamlformat_parser_extended.Lexer.Error(_, _). The printer registered viaLocation.register_error_of_exnlives in a separate table fromPrintexc, so it was never consulted.Location.error_of_exn: if a printer is registered, format itsmainmessage; otherwise fall back toExn.pp. HandlesLexer.Errorand any other registered exception without per-variant enumeration.doc_lexer_errors.mld) covering the variants exercised.Test plan
dune builddune runtest(new.errfixtures updated)