Add lint to check for known cross-module internal packages (#4426)

* Add depguard conf for cross-mod internal pkg check

* Apply feedback

* Apply suggestions from code review

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>

.golangci.yml

@@ -73,6 +73,56 @@ linters-settings:
           - pkg: "crypto/md5"
           - pkg: "crypto/sha1"
           - pkg: "crypto/**/pkix"
+      otlp-internal:
+        files:
+          - "!**/exporters/otlp/internal/**/*.go"
+          # TODO: remove the following when otlpmetric/internal is removed.
+          - "!**/exporters/otlp/otlpmetric/internal/oconf/envconfig.go"
+          - "!**/exporters/otlp/otlpmetric/internal/oconf/options.go"
+          - "!**/exporters/otlp/otlpmetric/internal/oconf/options_test.go"
+          - "!**/exporters/otlp/otlpmetric/internal/otest/client_test.go"
+        deny:
+          - pkg: "go.opentelemetry.io/otel/exporters/otlp/internal"
+            desc: Do not use cross-module internal packages.
+      otlptrace-internal:
+        files:
+          - "!**/exporters/otlp/otlptrace/*.go"
+          - "!**/exporters/otlp/otlptrace/internal/**.go"
+        deny:
+          - pkg: "go.opentelemetry.io/otel/exporters/otlp/otlptrace/internal"
+            desc: Do not use cross-module internal packages.
+      otlpmetric-internal:
+        files:
+          - "!**/exporters/otlp/otlpmetric/internal/*.go"
+          - "!**/exporters/otlp/otlpmetric/internal/**/*.go"
+        deny:
+          - pkg: "go.opentelemetry.io/otel/exporters/otlp/otlpmetric/internal"
+            desc: Do not use cross-module internal packages.
+      otel-internal:
+        files:
+          - "**/sdk/*.go"
+          - "**/sdk/**/*.go"
+          - "**/exporters/*.go"
+          - "**/exporters/**/*.go"
+          - "**/schema/*.go"
+          - "**/schema/**/*.go"
+          - "**/metric/*.go"
+          - "**/metric/**/*.go"
+          - "**/bridge/*.go"
+          - "**/bridge/**/*.go"
+          - "**/example/*.go"
+          - "**/example/**/*.go"
+          - "**/trace/*.go"
+          - "**/trace/**/*.go"
+        deny:
+          - pkg: "go.opentelemetry.io/otel/internal$"
+            desc: Do not use cross-module internal packages.
+          - pkg: "go.opentelemetry.io/otel/internal/attribute"
+            desc: Do not use cross-module internal packages.
+          - pkg: "go.opentelemetry.io/otel/internal/internaltest"
+            desc: Do not use cross-module internal packages.
+          - pkg: "go.opentelemetry.io/otel/internal/matchers"
+            desc: Do not use cross-module internal packages.
   godot:
     exclude:
       # Exclude links.