cmd/go: print hint when 'go install' run without version outside module

If 'go install' is invoked in module mode outside a module with a
package that could only be loaded from a module, it will now suggest
running 'go install pkg@latest'.

'go install' will still work outside a module on packages in std and
cmd, as well as .go files specified on the command line.

Fixes #42638

Change-Id: Ib0963935f028b7656178bc04a279b1114de35fbb
Reviewed-on: https://go-review.googlesource.com/c/go/+/277355
Run-TryBot: Jay Conrod <jayconrod@google.com>
Trust: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/src/cmd/go/testdata/script/mod_outside.txt b/src/cmd/go/testdata/script/mod_outside.txt
index 28379ab40d..8f01b5d242 100644
--- a/src/cmd/go/testdata/script/mod_outside.txt
+++ b/src/cmd/go/testdata/script/mod_outside.txt
@@ -189,13 +189,16 @@ exists $GOPATH/bin/printversion$GOEXE
 
 # 'go install' should fail if a package argument must be resolved to a module.
 ! go install example.com/printversion
-stderr 'no required module provides package example.com/printversion: working directory is not part of a module'
+stderr '^go install: version is required when current directory is not in a module\n\tTry ''go install example.com/printversion@latest'' to install the latest version$'
 
 # 'go install' should fail if a source file imports a package that must be
 # resolved to a module.
 ! go install ./needmod/needmod.go
 stderr 'needmod[/\\]needmod.go:10:2: no required module provides package example.com/version: working directory is not part of a module'
 
+# 'go install' should succeed with a package in GOROOT.
+go install cmd/addr2line
+! stderr .
 
 # 'go run' with a verison should fail due to syntax.
 ! go run example.com/printversion@v1.0.0