Mango match_failures/2 function - #6080
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Rather than returning a boolean to indicate just success or failure, `mango_selector:match/2` now returns a list of "failures" describing the ways in which the selector failed to match the input. If this list is empty, the match was a success.
We will need to pass other things around between `match` calls as well the current `Cmp` function, so here we replace this argument with a `#ctx` record that intially just contains a `cmp` field.
To give detailed feedback to the caller, the `#ctx` argument to `mango_selector:match/3` now records the path that was taken to reach each value, and this path is added to the `#failure` records. Each path segment is either a binary, if it represents an object property, or an integer if it represents an array index. Items are pushed on the front of `#ctx.path` as this is faster than pushing onto the back of a list. This list can then be reversed once the final list of failures has been generated, before the failures are presented to the caller.
Collecting detailed `#failure` records rather than a boolean true/false
when evaluating selectors imposes a performance penalty, so we would
like to only do this when a selector is used for a VDU, not when it is
used for indexing/filtering.
To this end we introduce "verbose" mode signalled via the `#ctx.verbose`
field, and each branch of `mango_selector:match/3` now has 3 distinct
versions:
- `#ctx{verbose = false}`: this is the original version that returns
true/false, taken when a selector is used for Mango queries.
- `#ctx{verbose = true, negate = false}`: verbose mode, when the
operator is not negated by an enclosing `$not` operator. Returns a
list of `#failure` records which may be empty.
- `#ctx{verbose = true, negate = true}`: verbose mode, when the operator
is negated by an enclosing `$not` operator. Returns a list of
`#failure` records.
The different negation modes are needed because, in order to generate
meaningful failure messages, we need to record whether an operator was
negated. The behaviour of combinators like `$and`, `$or`, `$allMatch`
and `$elemMatch` means not all `$not` operators can be normalized out of
the selector before evaluation. Instead, when we encounter a `$not`
during evaluation, we flip the `#ctx.negate` field before evaluating the
inner operator.
Until now, document updates rejected by a Mango VDU returned an opaque "forbidden" message to the client. This commit adds a detailed list of failures, obtained by converting the `#failure` records returned by `mango_selector:match/3` into human-readable messages.
…ct if the doc is newly created
Currently, when a design doc is updated, we validate the `map` and `reduce` fields, but not `validate_doc_update`. Instead, trying to update any other doc while an invalid `validate_doc_update` exists will trigger an error. This comment makes VDU validation more 'eager' by performing it when the ddoc itself is updated. Normal doc writes will still trigger an error if an invalid `validate_doc_update` already exists, but now we try to prevent this happening by validating VDUs when they are first created.
…keyMapMatch") should be considered successful when applied to values of the wrong type
…lements when reporting VDU failures
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This PR has the same content as #5858, it is just in a branch in the
apacherepo to see if this resolves problems with CI.