Missing experimental functions from Prometheus functions.go (mad_over_time, info, histogram_quantiles, ts_of_*, …)

[zzylol]

Summary

promql-parser 0.9.0 rejects several PromQL functions that exist in Prometheus's current promql/parser/functions.go as unknown function. All are marked Experimental: true upstream, so they appear to be additions made after the 0.9 function table was last synced.

I found these by running Prometheus's own engine test corpus through promql-parser 0.9: I extracted every eval expression from promql/promqltest/testdata/*.test (1823 deduped expressions) and parsed each. 316 fail to parse; the unknown-function failures cluster in functions.test, info.test, and histograms.test.

Functions in Prometheus main but not in promql-parser 0.9

Diff of the two function tables (Prometheus 87 vs promql-parser 76):

Function	ArgTypes	Variadic	Returns	Experimental
mad_over_time	(matrix)	—	vector	yes
first_over_time	(matrix)	—	vector	yes
ts_of_first_over_time	(matrix)	—	vector	yes
ts_of_last_over_time	(matrix)	—	vector	yes
ts_of_max_over_time	(matrix)	—	vector	yes
ts_of_min_over_time	(matrix)	—	vector	yes
histogram_quantiles	(vector, string, scalar, scalar…)	9	vector	yes
info	(vector, vector)	1	vector	yes
max_of	(scalar, scalar)	—	scalar	yes
min_of	(scalar, scalar)	—	scalar	yes
start	()	—	scalar	yes
end	()	—	scalar	yes
step	()	—	scalar	yes
range	()	—	scalar	yes

Reproduction

use promql_parser::parser;
for q in [
    "mad_over_time(metric[5m])",
    "info(metric, {k=\"v\"})",
    "histogram_quantiles(metric, \"q\", 0.5, 0.9)",
    "ts_of_max_over_time(metric[5m])",
    "max_of(scalar(a), scalar(b))",
] {
    assert!(parser::parse(q).is_err(), "{q} unexpectedly parsed");
}

(promql-parser = "0.9.0")

Happy to send a PR adding the missing function-table entries if that's helpful.

[evenyag]

#138 may address this.