refactor(GoMod): Disable any GOPROXY

This ensures that the `.info` files for all modules, which
get created by the Go command line tools under '$GOPATH/pkg/mod',
contain the VCS info. When using a Go proxy this is not guaranteed and
depends on the actual proxy instance, see [1]. This comes at the price
of increased execution time.

As the user's environment may likely be configured to use a GOPROXY,
which is the default, use an empty directory to not mix-up newly cached
files with already existing ones which might have been created using a
Go proxy and therefore may lack the VCS info.

This prepares for using the Go tooling to determine the VCS info instead
of using ORT's partial reimplementation of that.

[1]: golang/go#44742 (comment)
[2]: golang/go#18387

Signed-off-by: Frank Viernau <[email protected]>

analyzer/src/main/kotlin/managers/GoMod.kt

@@ -54,6 +54,7 @@ import org.ossreviewtoolkit.utils.common.Os
 import org.ossreviewtoolkit.utils.common.splitOnWhitespace
 import org.ossreviewtoolkit.utils.common.stashDirectories
 import org.ossreviewtoolkit.utils.common.withoutSuffix
+import org.ossreviewtoolkit.utils.ort.createOrtTempDir
 
 /**
  * The [Go Modules](https://github.com/golang/go/wiki/Modules) package manager for Go.
@@ -81,6 +82,15 @@ class GoMod(
         ) = GoMod(type, analysisRoot, analyzerConfig, repoConfig)
     }
 
+    private val goPath by lazy { createOrtTempDir() }
+
+    private val environment by lazy {
+        mapOf(
+            "GOPROXY" to "direct",
+            "GOPATH" to goPath.absolutePath
+        )
+    }
+
     override fun command(workingDir: File?) = "go"
 
     override fun getVersionArguments() = "version"
@@ -339,7 +349,8 @@ class GoMod(
         return firstProxy.ifBlank { DEFAULT_GO_PROXY }
     }
 
-    private fun runGo(vararg args: CharSequence, workingDir: File? = null) = run(args = args, workingDir = workingDir)
+    private fun runGo(vararg args: CharSequence, workingDir: File? = null) =
+        run(args = args, workingDir = workingDir, environment = environment)
 }
 
 /**