1 files changed, 25 insertions, 12 deletions

diff --git a/src/cmd/go/internal/modget/get.go b/src/cmd/go/internal/modget/get.go
index 574f3e194d..dccacd3d1e 100644
--- a/src/cmd/go/internal/modget/get.go
+++ b/src/cmd/go/internal/modget/get.go
@@ -176,20 +176,23 @@ packages or when the mirror refuses to serve a public package (typically for
 legal reasons). Therefore, clients can still access public code served from
 Bazaar, Fossil, or Subversion repositories by default, because those downloads
 use the Go module mirror, which takes on the security risk of running the
-version control commands, using a custom sandbox.
+version control commands using a custom sandbox.
 
 The GOVCS variable can be used to change the allowed version control systems
 for specific packages (identified by a module or import path).
-The GOVCS variable applies both when using modules and when using GOPATH.
-When using modules, the patterns match against the module path.
-When using GOPATH, the patterns match against the import path
-corresponding to the root of the version control repository.
+The GOVCS variable applies when building package in both module-aware mode
+and GOPATH mode. When using modules, the patterns match against the module path.
+When using GOPATH, the patterns match against the import path corresponding to
+the root of the version control repository.
 
 The general form of the GOVCS setting is a comma-separated list of
 pattern:vcslist rules. The pattern is a glob pattern that must match
 one or more leading elements of the module or import path. The vcslist
 is a pipe-separated list of allowed version control commands, or "all"
-to allow use of any known command, or "off" to allow nothing.
+to allow use of any known command, or "off" to disallow all commands.
+Note that if a module matches a pattern with vcslist "off", it may still be
+downloaded if the origin server uses the "mod" scheme, which instructs the
+go command to download the module using the GOPROXY protocol.
 The earliest matching pattern in the list applies, even if later patterns
 might also match.
 
@@ -197,7 +200,7 @@ For example, consider:
 
 	GOVCS=github.com:git,evil.com:off,*:git|hg
 
-With this setting, code with an module or import path beginning with
+With this setting, code with a module or import path beginning with
 github.com/ can only use git; paths on evil.com cannot use any version
 control command, and all other paths (* matches everything) can use
 only git or hg.
@@ -380,10 +383,9 @@ func runGet(ctx context.Context, cmd *base.Command, args []string) {
 		pkgs := load.PackagesAndErrors(ctx, pkgPatterns)
 		load.CheckPackageErrors(pkgs)
 		work.InstallPackages(ctx, pkgPatterns, pkgs)
-		// TODO(#40276): After Go 1.16, print a deprecation notice when building
-		// and installing main packages. 'go install pkg' or
-		// 'go install pkg@version' should be used instead.
-		// Give the specific argument to use if possible.
+		// TODO(#40276): After Go 1.16, print a deprecation notice when building and
+		// installing main packages. 'go install pkg' or 'go install pkg@version'
+		// should be used instead. Give the specific argument to use if possible.
 	}
 
 	if !modload.HasModRoot() {
@@ -1453,7 +1455,18 @@ func (r *resolver) checkPackagesAndRetractions(ctx context.Context, pkgPatterns
 			}
 		}
 		for _, pkg := range pkgs {
-			if _, _, err := modload.Lookup("", false, pkg); err != nil {
+			if dir, _, err := modload.Lookup("", false, pkg); err != nil {
+				if dir != "" && errors.Is(err, imports.ErrNoGo) {
+					// Since dir is non-empty, we must have located source files
+					// associated with either the package or its test — ErrNoGo must
+					// indicate that none of those source files happen to apply in this
+					// configuration. If we are actually building the package (no -d
+					// flag), the compiler will report the problem; otherwise, assume that
+					// the user is going to build or test it in some other configuration
+					// and suppress the error.
+					continue
+				}
+
 				base.SetExitStatus(1)
 				if ambiguousErr := (*modload.AmbiguousImportError)(nil); errors.As(err, &ambiguousErr) {
 					for _, m := range ambiguousErr.Modules {