cmd/go: make hints in error messages more consistent

* All commands the user can run to fix the problem now appear alone on
  a separate line after a tab.
* Removed -d from 'go get' commands.
* Replaced 'go mod tidy' with 'go mod download $modpath' when a
  package might be provided by a module missing a sum.
* Errors about 'path@version' syntax are more explicit.

Fixes #29415
Fixes #42087
Fixes #43430
Fixes #43523

Change-Id: I4427c2c4506a727a2c727d652fd2d506bb134d3b
Reviewed-on: https://go-review.googlesource.com/c/go/+/282121
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/cmd/go/internal/modload/vendor.go b/src/cmd/go/internal/modload/vendor.go
index 80d49053c6..d8fd91f1fe 100644
--- a/src/cmd/go/internal/modload/vendor.go
+++ b/src/cmd/go/internal/modload/vendor.go
@@ -214,6 +214,6 @@ func checkVendorConsistency() {
 	}
 
 	if vendErrors.Len() > 0 {
-		base.Fatalf("go: inconsistent vendoring in %s:%s\n\nrun 'go mod vendor' to sync, or use -mod=mod or -mod=readonly to ignore the vendor directory", modRoot, vendErrors)
+		base.Fatalf("go: inconsistent vendoring in %s:%s\n\n\tTo ignore the vendor directory, use -mod=readonly or -mod=mod.\n\tTo sync the vendor directory, run:\n\t\tgo mod vendor", modRoot, vendErrors)
 	}
 }