cmd/go: report 'go get' errors for absolute paths outside module root

'go get' will now check absolute paths without wildcards the same way
it checks relative paths. modload.DirImportPath may be used for both
without converting path separators.

Fixes #38038

Change-Id: I453299898ece58f3b5002a5e80021d6bfe815fdd
Reviewed-on: https://go-review.googlesource.com/c/go/+/226857
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

2 files changed, 24 insertions, 12 deletions

diff --git a/src/cmd/go/internal/modget/get.go b/src/cmd/go/internal/modget/get.go
index 8ff442ac73..6ef64cb981 100644
--- a/src/cmd/go/internal/modget/get.go
+++ b/src/cmd/go/internal/modget/get.go
@@ -326,15 +326,18 @@ func runGet(cmd *base.Command, args []string) {
 		// patterns like golang.org/x/tools/..., which can't be expanded
 		// during package loading until they're in the build list.
 		switch {
-		case search.IsRelativePath(path):
-			// Relative paths like ../../foo or ../../foo... are restricted to
-			// matching packages in the main module. If the path is explicit and
-			// contains no wildcards (...), check that it is a package in
-			// the main module. If the path contains wildcards but matches no
-			// packages, we'll warn after package loading.
+		case filepath.IsAbs(path) || search.IsRelativePath(path):
+			// Absolute paths like C:\foo and relative paths like ../foo...
+			// are restricted to matching packages in the main module. If the path
+			// is explicit and contains no wildcards (...), check that it is a
+			// package in the main module. If the path contains wildcards but
+			// matches no packages, we'll warn after package loading.
 			if !strings.Contains(path, "...") {
-				pkgPath := modload.DirImportPath(filepath.FromSlash(path))
-				if pkgs := modload.TargetPackages(pkgPath); len(pkgs) == 0 {
+				var pkgs []string
+				if pkgPath := modload.DirImportPath(path); pkgPath != "." {
+					pkgs = modload.TargetPackages(pkgPath)
+				}
+				if len(pkgs) == 0 {
 					abs, err := filepath.Abs(path)
 					if err != nil {
 						abs = path
@@ -520,7 +523,7 @@ func runGet(cmd *base.Command, args []string) {
 					// If the pattern did not match any packages, look up a new module.
 					// If the pattern doesn't match anything on the last iteration,
 					// we'll print a warning after the outer loop.
-					if !search.IsRelativePath(arg.path) && !match.IsLiteral() && arg.path != "all" {
+					if !match.IsLocal() && !match.IsLiteral() && arg.path != "all" {
 						addQuery(&query{querySpec: querySpec{path: arg.path, vers: arg.vers}, arg: arg.raw})
 					} else {
 						for _, err := range match.Errs {
diff --git a/src/cmd/go/testdata/script/mod_get_main.txt b/src/cmd/go/testdata/script/mod_get_main.txt
index 403abcd28b..408a5b51c8 100644
--- a/src/cmd/go/testdata/script/mod_get_main.txt
+++ b/src/cmd/go/testdata/script/mod_get_main.txt
@@ -1,9 +1,18 @@
 env GO111MODULE=on
-[short] skip
+cp go.mod.orig go.mod
+
+# relative and absolute paths must be within the main module.
+! go get -d ..
+stderr '^go get \.\.: path '$WORK'[/\\]gopath is not a package in module rooted at '$WORK'[/\\]gopath[/\\]src$'
+! go get -d $WORK
+stderr '^go get '$WORK': path '$WORK' is not a package in module rooted at '$WORK'[/\\]gopath[/\\]src$'
+! go get -d ../...
+stderr '^go get: pattern \.\./\.\.\.: directory prefix \.\. outside available modules$'
+! go get -d $WORK/...
+stderr '^go get: pattern '$WORK'[/\\]\.\.\.: directory prefix \.\.[/\\]\.\. outside available modules$'
 
 # @patch and @latest within the main module refer to the current version.
 # The main module won't be upgraded, but missing dependencies will be added.
-cp go.mod.orig go.mod
 go get -d rsc.io/x
 grep 'rsc.io/quote v1.5.2' go.mod
 go get -d rsc.io/x@upgrade
@@ -18,7 +27,7 @@ cp go.mod.orig go.mod
 stderr '^go get rsc.io/x@latest: can.t request explicit version of path in main module$'
 
 # The main module cannot be updated to a specific version.
-! go get rsc.io/x@v0.1.0
+! go get -d rsc.io/x@v0.1.0
 stderr '^go get rsc.io/x@v0.1.0: can.t request explicit version of path in main module$'
 ! go get -d rsc.io/x@v0.1.0
 stderr '^go get rsc.io/x@v0.1.0: can.t request explicit version of path in main module$'