Symfony\Component\Yaml\Inline::evaluateScalar() breaks ISO 8601 dates

[bartfeenstra]

Symfony\Component\Yaml\Inline::evaluateScalar() uses Symfony\Component\Yaml\Inline::getTimestampRegex() to determine whether a scalar value contains a date in what seems to be the ISO 8601 format (getTimestampRegex() is badly documented) and if it does, it converts it to a Unix timestamp.
The problem is that this conversion is conceptually impossible for a number of reasons:

• ISO 8601 dates and Unix timestamps use different formats. Converting one to the other may break systems that expect a particular format.
• Unix timestamps do not support dates before 1970, while ISO 8601 does. This means data loss.

Suggested solution: remove the feature entirely.

[stof]

The feature should not be removed as handling ISO 8601 values a dates is part of the YAML spec. If you want to keep the string, you have to quote it.

[bartfeenstra]

I might not be a YAML expert, but how is converting a value that can or cannot (e.g. dates before 1970) be converted to a Unix timestamp to a Unix timestamp part of the specifications? I did a quick search of the 1.0, 1.1 and 1.2 documentation and couldn't find anything about special handling for ISO 8601 or Unix timestamps.

[asm89]

@bartfeenstra Dates before 1970 are represented by negative numbers. See the PR I created with a test showing that dates before 1970 work.

Are you having issues with this?

[bartfeenstra]

It appears that YYYY-MM-DD formats need to be quoted so Yaml doesn't convert them. YYYY-MM formats can be unquoted. My problems occured after manually altering some configuration files and not quoting YYYY-MM-DDD formats. A classic example of pebkac.

Thank you, stof and asm89, for your time spent on this issue!

Now that my issues are solved, I still have a few questions though:

• Unix timestamps in PHP, which are essentially 32bits signed integers, have a very limited minimum value. -2147483647 (minimum value) / 86400 (number of seconds in a day) / 365 (days in a year) = roughly 68 years before 1970, so when converting any ISO8601 date before roughly 1902 on a 32bit system, this should result in an overflow. On 64bit systems the range of a Unix timestamp exceeds that of the default ISO 8601 format and this problem does not occur.
• Why does Yaml convert some date formats (Symfony\Component\Yaml\Inline::getTimestampRegex() says "Unix timestamp", which is incorrect, not does it really describe what the pattern should match), but not all? To be more specific: why does it convert YYYY-MM-DD, but not YYYY-MM?

[stof]

@bartfeenstra because of the format specified in the YAML spec for timestamps: http://www.yaml.org/spec/1.2/spec.html#id2761573