Prototype info PromQL function

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

docs/querying/functions.md

@@ -421,6 +421,11 @@ by the number of seconds under the specified time range window, and should be
 used primarily for human readability.  Use `rate` in recording rules so that
 increases are tracked consistently on a per-second basis.
 
+## `info()`
+
+For each time series in `v`, `info(v instant-vector, [label-selector string])` finds all info metrics with corresponding
+identifying labels, and adds the union of their data labels to the time series, that gets returned.
+
 ## `irate()`
 
 `irate(v range-vector)` calculates the per-second instant rate of increase of

prompb/types.proto

@@ -39,12 +39,12 @@ message MetricMetadata {
 }
 
 message Sample {
-  double value    = 1;
+  double value                     = 1;
   // timestamp is in ms format, see model/timestamp/timestamp.go for
   // conversion from time.Time to Prometheus timestamp.
-  int64 timestamp = 2;
+  int64 timestamp                  = 2;
   // The set of identifying labels for info metrics, as array indices.
-  repeated int32 identifyingLabels        = 3;
+  repeated int32 identifyingLabels = 3;
 }
 
 message Exemplar {
@@ -125,10 +125,10 @@ message BucketSpan {
 message TimeSeries {
   // For a timeseries to be valid, and for the samples and exemplars
   // to be ingested by the remote system properly, the labels field is required.
-  repeated Label labels             = 1 [(gogoproto.nullable) = false];
-  repeated Sample samples           = 2 [(gogoproto.nullable) = false];
-  repeated Exemplar exemplars       = 3 [(gogoproto.nullable) = false];
-  repeated Histogram histograms     = 4 [(gogoproto.nullable) = false];
+  repeated Label labels         = 1 [(gogoproto.nullable) = false];
+  repeated Sample samples       = 2 [(gogoproto.nullable) = false];
+  repeated Exemplar exemplars   = 3 [(gogoproto.nullable) = false];
+  repeated Histogram histograms = 4 [(gogoproto.nullable) = false];
 }
 
 message Label {