semconv: Add metric generation (#4880)

* Adds some basic constants for metrics utilizing a new jinja template

* Updates generated comments with more explicit nomenclature; Adds Unit and Description consts for each metric; append 'Name' to metric const instead of 'Key'

* Update CHANGELOG

* fix overlooked merge conflict

* change the types of generated consts to string; format generation to handle empty stability and descriptions

* trim trailing (repeated) periods in the description

* manual formatting of some proper nouns; simplify the license header

* update metrics file with concise generated license header

* revert special formatting logic for JVM and ASPNETCore

* Update CHANGELOG.md

* Update CHANGELOG.md

Co-authored-by: Damien Mathieu <42@dmathieu.com>

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>
Co-authored-by: Sam Xie <sam@samxie.me>
Co-authored-by: Damien Mathieu <42@dmathieu.com>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -26,6 +26,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Add support for `AddLink` to `go.opentelemetry.io/otel/bridge/opencensus`. (#5116)
 - Add `String` method to `Value` and `KeyValue` in `go.opentelemetry.io/otel/log`. (#5117)
 - Add Exemplar support to `go.opentelemetry.io/otel/exporters/prometheus`. (#5111)
+- Add metric semantic conventions to `go.opentelemetry.io/otel/semconv/v1.24.0`. Future `semconv` packages will include metric semantic conventions as well. (#4528)
 
 ### Changed
 

Makefile

@@ -280,6 +280,7 @@ semconv-generate: | $(SEMCONVGEN) $(SEMCONVKIT)
 	$(SEMCONVGEN) -i "$(OTEL_SEMCONV_REPO)/model/." --only=attribute_group -p conventionType=trace -f attribute_group.go -t "$(SEMCONVPKG)/template.j2" -s "$(TAG)"
 	$(SEMCONVGEN) -i "$(OTEL_SEMCONV_REPO)/model/." --only=event -p conventionType=event -f event.go -t "$(SEMCONVPKG)/template.j2" -s "$(TAG)"
 	$(SEMCONVGEN) -i "$(OTEL_SEMCONV_REPO)/model/." --only=resource -p conventionType=resource -f resource.go -t "$(SEMCONVPKG)/template.j2" -s "$(TAG)"
+	$(SEMCONVGEN) -i "$(OTEL_SEMCONV_REPO)/model/." --only=metric  -f metric.go -t "$(SEMCONVPKG)/metric_template.j2" -s "$(TAG)"
 	$(SEMCONVKIT) -output "$(SEMCONVPKG)/$(TAG)" -tag "$(TAG)"
 
 .PHONY: gorelease

semconv/metric_template.j2

@@ -0,0 +1,49 @@
+{%- macro to_go_name(fqn) -%}
+{{fqn | replace(".", " ") | replace("_", " ") | title | replace(" ", "")}}
+{%- endmacro -%}
+{%- macro it_reps(brief) -%}
+It represents {% if brief[:2] == "A " or brief[:3] == "An " or brief[:4] == "The " -%}
+  {{ brief[0]|lower }}{{ brief[1:] }}
+{%- else -%}
+  the {{ brief[0]|lower }}{{ brief[1:] }}
+{%- endif -%}
+{%- endmacro -%}
+{%- macro keydoc(metric) -%}
+{%- if metric.stability|string() == "StabilityLevel.DEPRECATED" or not metric.brief-%}
+{{ to_go_name(metric.metric_name) }} is the metric conforming to the "{{ metric.metric_name}}" semantic conventions.
+{%- else -%}
+{{ to_go_name(metric.metric_name) }} is the metric conforming to the "{{ metric.metric_name}}" semantic conventions. {{ it_reps(metric.brief)|trim(".") }}.
+{%- endif %}
+{%- endmacro -%}
+{%- macro format_stability(stability) -%}
+{%- if not stability -%}
+Experimental
+{%- else -%}
+{{ stability|replace("StabilityLevel.", "")|capitalize() }}
+{%- endif %}
+{%- endmacro -%}
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// Code generated from semantic convention specification. DO NOT EDIT.
+
+package semconv  // import [[IMPORTPATH]]
+
+const (
+{% for id in semconvs %}
+{%- if semconvs[id].GROUP_TYPE_NAME == 'metric' %}{% set metric = semconvs[id] %}
+  // {{ keydoc(metric) | wordwrap(76, break_long_words=false, break_on_hyphens=false, wrapstring="\n// ") }}
+  // Instrument: {{ metric.instrument }}
+  // Unit: {{ metric.unit }}
+  // Stability: {{ format_stability(metric.stability) }}
+{%- if not metric.brief %}
+  // NOTE: The description (brief) for this metric is not defined in the semantic-conventions repository.
+{%- endif %}
+  {{to_go_name(metric.metric_name)}}Name = "{{metric.metric_name}}"
+  {{to_go_name(metric.metric_name)}}Unit = "{{metric.unit}}"
+{%- if metric.brief %}
+  {{to_go_name(metric.metric_name)}}Description = "{{metric.brief}}"
+{%- endif %}
+{%- endif %}
+{% endfor %}
+)