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Clear parse errors #4
Description
Problem
Malformed input either throws an exception that says nothing about the input, or, worse, is silently read as something else. Tested against v0.1.2:
Silently accepted (a wrong answer with no error):
| Input | Read as |
|---|---|
{1,2 |
{1} |
{1,2}junk |
{1,2}jun} |
{1,(2))} |
{1,(2),)} |
Thrown, but with the wrong type or no useful message:
| Case | Exception |
|---|---|
"" |
IndexOutOfRangeException |
{(1,2},3) |
bare System.Exception: "Braces not matched" |
| an unmatched closing brace | InvalidOperationException from Stack.Pop ("Stack empty") |
| shape mismatch | InvalidOperationException: "Cannot enumerate over a value", "Cannot index into a set" (stack traces in ReduxISU/Redux#577) |
failed subset constraint |
message literally says PLACEHOLDER: "Constraint S subset PLACEHOLDER failed because x was not a subset of PLACEHOLDER" |
Wanted
- Reject malformed input. Unbalanced braces, trailing characters and empty input are errors, never a best guess.
- One error type. Throw a dedicated parse exception for every bad-input case, including shape mismatches and failed constraints. Never
System.Exception,InvalidOperationExceptionorIndexOutOfRangeException. - Say what's wrong. Include the position, what was expected and what was found, e.g.
expected , or } at position 14, found x. Name the set in constraint failures instead ofPLACEHOLDER.
Redux context
- Redux passes the message straight into the 400's detail.
- Without a dedicated type, Redux has to guess whether an exception means bad input or a real bug, which is the compromise in Backend bug fixes: clean 400s for bad input, solver fixes, parser hardening Redux#624.
Activity
Trosper3 commentedon Oct 16, 2026
A gap on the definition side, found by the coverage tests in #39:
parse()accepts malformed definition strings.{N | N is set(missing brace),{N | N is set#}and{N | N is set}}are printed to the console by ANTLR's default error listener and then parsed as best it can, which is the "best guess" this issue rules out.Definition(#24) already rejects the same strings with aFormatExceptionand the position.Fixing this before 0.2.0:
StringParserwill reject a malformed definition the same wayDefinitiondoes.ConstraintGapTests.cshas the skipped test to un-skip.