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Altering callmaps

Intro

One of the first things most contributors start with is proposing changes to callmaps.

Callmap is a data file (formatted as a PHP file returning an array) that tells Psalm what arguments function/method takes and what it returns.

There are two full callmaps (CallMap.php and CallMap_historical.php) in dictionaries folder, and a number of delta files that provide information on how signatures changed in various PHP versions. CallMap_historical has signatures as they were in PHP 7.0, CallMap.php contains current signatures (for PHP 8.1 at the time of writing).

Full callmap format

Full callmaps (CallMap.php and CallMap_historical.php) have function/method names as keys and an array representing the corresponding signature as a value.

First element of that value is a return type (it also doesn't have a key), and subsequent elements represent function/method parameters. Parameter name for an optional parameter is postfixed with =.

Delta file format

Delta files (named CallMap_<PHP major version><PHP minor version>_delta.php) list changes that happened in the corresponding PHP version. There are three section with self-explanatory names: added (for functions/methods that were added in that PHP version), removed (for those that were removed) and changed.

Entry format for removed and added section matches that of a full callmap, while changed entries list old and new signatures.

How Psalm uses delta files

When the current PHP version is set to something other than the latest PHP version supported by Psalm, it needs to process delta files to arrive at a version of callmap matching the one that is used during analysis. Psalm uses the following process to do that:

  1. Read CallMap.php (Note: it's the one having the latest signatures).
  2. If it matches configured PHP version, use it.
  3. If the callmap delta for previous PHP version exists, read that.
  4. Take previous callmap delta and apply it in reverse order. That is, entries in removed section are added, those in added section are removed and changed.new signatures in the current callamp are replaced with changed.old.
  5. Goto 2

Consistent histories

To make sure there are no mismatches in deltas and the callmap, CI validates that all function/method entries have consistent histories. E.g. that the signature in changed.new matches the one in CallMap.php, the removed entries are actually absent from CallMap.php and so on.

Typical changes

To put that into practical perspective, let's see how a couple of typical callmap changes may look like.

Adding a new function

Say, there's a function added in PHP 8.1, e.g. array_is_list(). Add it to the CallMap_81_delta.php (as it was introduced in PHP 8.1), and CallMap.php (as it exists in the latest PHP version). Here's the PR that does it.

Correcting the function signature

Assume you found an incorrect signature, the one that was always different to what we currently have in Psalm. This will need a change to CallMap_historical.php (as the signature was always that way) and CallMap.php (as the signature is still valid). Here's the PR that does it.

If function signature is correct for an older version but has changed since you will need to edit the delta for PHP version where signature changed and CallMap.php (as this new signature is still valid). Here's the PR that does it (makes timestamp nullable).