mock: do not let a surplus matcher match a missing argument - #1938
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brackendawson merged 2 commits intoAug 24, 2026
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Arguments.Diff used the plain string "(Missing)" as the sentinel for an
argument that one side does not have. A surplus mock.Anything,
mock.AnythingOfType("string"), mock.IsType(""), or the literal string
"(Missing)" therefore matched an argument the caller never passed, so an
expectation with more arguments than the method takes passed silently.
mock.MatchedBy was handed the sentinel string as if it were a real
argument, and mock.FunctionalOptions() panicked on it.
The sentinel is now an unexported missingArgument type with no
constructor, so no expectation can hold a value equal to it. Diff also
reports a difference for a missing argument on either side before any
matcher is consulted, since differing arity is never a match.
Failure messages are unchanged: missing arguments still print as
"(Missing)".
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Summary
A matcher in a surplus position could match an argument that was never passed.
Changes
Arguments.Diffused the string"(Missing)"to stand in for an absent argument. That is now an unexportedmissingArgumenttype.Diffrecords the length mismatch before it consults any matcher.MatchedByis no longer called with the sentinel.missingArgument.String()returns(Missing).Motivation
With a plain string as the sentinel,
mock.Anything,mock.AnythingOfType("string"),mock.IsType("")and the literal"(Missing)"all matched an argument that did not exist, so anOncall listing too many arguments passed instead of failing.mock.FunctionalOptions()panicked on it.Related issues
Closes #1211
Closes #587