使用go get安装OPA rego库时遇无Go源文件错误，求排查方案

问题 #

尝试使用命令go get github.com/open-policy-agent/opa/rego安装OPA库时出现报错，错误信息：

build github.com/open-policy-agent/opa/capabilities: cannot load github.com/open-policy-agent/opa/capabilities: no Go source files

命令执行完整输出：

-bash-4.2$ go get github.com/open-policy-agent/opa/rego
go: finding github.com/open-policy-agent/opa/rego latest
go: finding github.com/open-policy-agent/opa v0.53.1
go: downloading github.com/open-policy-agent/opa v0.53.1
go: extracting github.com/open-policy-agent/opa v0.53.1
go: downloading github.com/gorilla/mux v1.8.0
go: downloading github.com/rcrowley/go-metrics v0.0.0-20200313005456-10cdbea86bc0
go: downloading github.com/sirupsen/logrus v1.9.2
go: downloading github.com/go-ini/ini v1.67.0
go: downloading go.opentelemetry.io/otel v1.14.0
go: extracting github.com/rcrowley/go-metrics v0.0.0-20200313005456-10cdbea86bc0
go: downloading github.com/prometheus/client_golang v1.15.1
go: downloading github.com/OneOfOne/xxhash v1.2.8
go: downloading gopkg.in/yaml.v2 v2.4.0
go: downloading github.com/gobwas/glob v0.2.3
go: extracting github.com/gorilla/mux v1.8.0
go: downloading github.com/tchap/go-patricia v2.2.6+incompatible
go: extracting github.com/prometheus/client_golang v1.15.1
go: extracting gopkg.in/yaml.v2 v2.4.0
go: extracting github.com/sirupsen/logrus v1.9.2
go: extracting github.com/OneOfOne/xxhash v1.2.8
go: extracting go.opentelemetry.io/otel v1.14.0
go: extracting github.com/tchap/go-patricia v2.2.6+incompatible
go: extracting github.com/go-ini/ini v1.67.0
go: downloading github.com/yashtewari/glob-intersection v0.1.0
go: downloading github.com/tchap/go-patricia/v2 v2.3.1
go: downloading github.com/ghodss/yaml v1.0.0
go: downloading github.com/agnivade/levenshtein v1.1.1
go: extracting github.com/tchap/go-patricia/v2 v2.3.1
go: downloading github.com/xeipuuv/gojsonreference v0.0.0-20180127040603-bd5ef7bd5415
go: extracting github.com/yashtewari/glob-intersection v0.1.0
go: extracting github.com/ghodss/yaml v1.0.0
go: extracting github.com/xeipuuv/gojsonreference v0.0.0-20180127040603-bd5ef7bd5415
go: extracting github.com/gobwas/glob v0.2.3
go: downloading github.com/xeipuuv/gojsonpointer v0.0.0-20190905194746-02993c407bfb
go: downloading golang.org/x/sys v0.8.0
go: extracting github.com/xeipuuv/gojsonpointer v0.0.0-20190905194746-02993c407bfb
go: extracting golang.org/x/sys v0.8.0
go: downloading google.golang.org/protobuf v1.30.0
go: downloading github.com/prometheus/client_model v0.3.0
go: downloading github.com/prometheus/common v0.42.0
go: downloading github.com/beorn7/perks v1.0.1
go: downloading github.com/cespare/xxhash v1.1.0
go: extracting github.com/agnivade/levenshtein v1.1.1
go: extracting github.com/prometheus/common v0.42.0
go: extracting github.com/beorn7/perks v1.0.1
go: extracting github.com/prometheus/client_model v0.3.0
go: extracting github.com/cespare/xxhash v1.1.0
go: downloading github.com/prometheus/procfs v0.9.0
go: downloading github.com/cespare/xxhash/v2 v2.2.0
go: extracting google.golang.org/protobuf v1.30.0
go: downloading github.com/golang/protobuf v1.5.3
go: extracting github.com/cespare/xxhash/v2 v2.2.0
go: extracting github.com/golang/protobuf v1.5.3
go: extracting github.com/prometheus/procfs v0.9.0
go: downloading go.opentelemetry.io/otel/sdk v1.14.0
go: extracting go.opentelemetry.io/otel/sdk v1.14.0
go: downloading github.com/go-logr/logr v1.2.4
go: extracting github.com/go-logr/logr v1.2.4
go: downloading github.com/go-logr/stdr v1.2.2
go: extracting github.com/go-logr/stdr v1.2.2
go: downloading github.com/matttproud/golang_protobuf_extensions v1.0.4
go: extracting github.com/matttproud/golang_protobuf_extensions v1.0.4
go: downloading go.opentelemetry.io/otel/trace v1.14.0
go: extracting go.opentelemetry.io/otel/trace v1.14.0
go: finding github.com/OneOfOne/xxhash v1.2.8
build github.com/open-policy-agent/opa/capabilities: cannot load github.com/open-policy-agent/opa/capabilities: no Go source files

系统信息：

-bash-4.2$ uname -a
Linux dev-rh72-tas-1.in.intinfra.com 3.10.0-327.el7.x86_64 #1 SMP Thu Oct 29 17:29:29 EDT 2015 x86_64 x86_64 x86_64 GNU/Linux

疑问：安装OPA是否有前置条件？安装过程中是否遗漏了步骤？

解决方法 #

核心问题原因 #

直接拉取rego子目录触发了Go Module的依赖解析异常，且capabilities目录在OPA v0.53.1中为生成代码目录，无原生Go源文件，导致编译失败。

正确安装步骤 #

1. 安装完整OPA模块：不要指定子目录，执行以下命令之一：

   # 安装最新版本
   go get github.com/open-policy-agent/opa@latest
   # 安装指定版本（如你尝试的v0.53.1）
   go get github.com/open-policy-agent/opa@v0.53.1
   

2. 导入rego包：安装完成后，在代码中直接导入即可使用：

   import "github.com/open-policy-agent/opa/rego"
   

前置条件检查 #

• Go版本要求：OPA v0.53.1需要Go 1.19及以上版本，CentOS 7默认Go版本较低，需手动升级到符合要求的版本。
• Go Module启用：执行go env GO111MODULE，若返回off，需先设置环境变量：

  export GO111MODULE=on
  

  再执行安装命令。

内容的提问来源于stack exchange，提问作者van neilsen