MCDC Coverage: instrument last boolean RHS operands from condition coverage by RenjiSann · Pull Request #124652 · rust-lang/rust (original) (raw)

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It took me some times to understand why this would not create an MCDC record for the first 2 conditions.

Actually, it's just because of operator's priority. The AST looks like this

Therefore, before the change,

• We would instrument ||'s LHS through then_else_break, which would not produce a record because there is only 1 condition (a)
• We would repeat the same for &&, its LHS being just b.

This emphasizes another weak point of the previous implementation :

let x = a && (b && ( c && (d && (e))));

This decision wasn't recorded at all by MCDC.