Set Go support policy to latest-2

Signed-off-by: Adrian Cole <adrian@tetrate.io>

.github/workflows/ci.yml

@@ -10,32 +10,31 @@ on:
 
 jobs:
   "CI":
-    env:
-      GO111MODULE: on
-    runs-on: ${{ matrix.os }}
+    name: ${{ matrix.platform.arch }}, ${{ matrix.platform.os }}, Go-${{ matrix.go-version }}
+    runs-on: ${{ matrix.platform.os }}
     strategy:
-      matrix:
-        os: [macos-latest, windows-latest, ubuntu-latest]
-        go: ["1.20"]
-        include:
-          - os: ubuntu-latest
-            go: "1.18"
-          - os: ubuntu-latest
-            go: "1.19"
+      matrix:  # Use versions consistent with zipkin-go's Go support policy.
+        platform:
+          - os: ubuntu-22.04
+            arch: amd64
+        go-version:
+          - "1.22"  # Current Go version
+          - "1.20"  # Floor Go version of zipkin-go (current - 2)
+
     steps:
       # Set fetch-depth: 0 to fetch commit history and tags for use in version calculation
       - name: Check out code
-        uses: actions/checkout@v2.3.4
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
 
       - name: Setup go
-        uses: actions/setup-go@v1
+        uses: actions/setup-go@v5
         with:
-          go-version: ${{ matrix.go }}
+          go-version: ${{ matrix.go-version }}
 
       - name: Lint files
-        uses: golangci/golangci-lint-action@v2
+        uses: golangci/golangci-lint-action@v4
         with:
           # Required: the version of golangci-lint is required and must be specified without patch version: we always use the latest patch version.
           version: latest

README.md

@@ -112,5 +112,17 @@ Producer digesting JSON V2 Spans. The reporter uses the
 [Sarama async producer](https://pkg.go.dev/github.com/IBM/sarama#AsyncProducer)
 underneath.
 
-## usage and examples
+## Usage and Examples
 [HTTP Server Example](examples/httpserver_test.go)
+
+## Go Support Policy
+
+zipkin-go follows the same version policy as Go's [Release Policy](https://go.dev/doc/devel/release):
+two versions. zipkin-go will ensure these versions work and bugs are valid if
+there's an issue with a current Go version.
+
+Additionally, zipkin-go intentionally delays usage of language or standard
+library features one additional version. For example, when Go 1.29 is released,
+zipkin-go can use language features or standard libraries added in 1.27. This
+is a convenience for embedders who have a slower version policy than Go.
+However, only supported Go versions may be used to raise support issues.

go.mod

@@ -1,6 +1,6 @@
 module github.com/openzipkin/zipkin-go
 
-go 1.18
+go 1.20
 
 require (
 	github.com/IBM/sarama v1.40.1