cmd/go: diagnose go.mod and vendor out of sync in std and cmd

The most common failure mode of the current std/cmd setup is
going to be people running "go get m@latest" and then not running
"go mod vendor" and being confused about getting the old m.
Diagnose and report what to do.

Also, having done the check, when in the standard library,
switch the go command to -mod=vendor mode.
This avoids some network accesses I saw when running
'go clean -modcache' before doing some work in cmd.

Change-Id: I0ba4a66637b67225a9b97a1c89f26f9015b41673
Reviewed-on: https://go-review.googlesource.com/c/go/+/174528
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/modload/init.go

@@ -376,6 +376,7 @@ func InitMod() {
 		excluded[x.Mod] = true
 	}
 	modFileToBuildList()
+	stdVendorMode()
 	WriteGoMod()
 }
 
@@ -383,7 +384,7 @@ func InitMod() {
 func modFileToBuildList() {
 	Target = modFile.Module.Mod
 	targetPrefix = Target.Path
-	if search.InDir(cwd, cfg.GOROOTsrc) != "" {
+	if rel := search.InDir(cwd, cfg.GOROOTsrc); rel != "" && rel != filepath.FromSlash("cmd/vet/all") {
 		targetInGorootSrc = true
 		if Target.Path == "std" {
 			targetPrefix = ""
@@ -397,6 +398,42 @@ func modFileToBuildList() {
 	buildList = list
 }
 
+// stdVendorMode applies inside $GOROOT/src.
+// It checks that the go.mod matches vendor/modules.txt
+// and then sets -mod=vendor unless this is a command
+// that has to do explicitly with modules.
+func stdVendorMode() {
+	if !targetInGorootSrc {
+		return
+	}
+	if cfg.CmdName == "get" || strings.HasPrefix(cfg.CmdName, "mod ") {
+		return
+	}
+
+	readVendorList()
+BuildList:
+	for _, m := range buildList {
+		if m.Path == "cmd" || m.Path == "std" {
+			continue
+		}
+		for _, v := range vendorList {
+			if m.Path == v.Path {
+				if m.Version != v.Version {
+					base.Fatalf("go: inconsistent vendoring in %s:\n"+
+						"\tgo.mod requires %s %s but vendor/modules.txt has %s.\n"+
+						"\trun 'go mod tidy; go mod vendor' to sync",
+						modRoot, m.Path, m.Version, v.Version)
+				}
+				continue BuildList
+			}
+		}
+		base.Fatalf("go: inconsistent vendoring in %s:\n"+
+			"\tgo.mod requires %s %s but vendor/modules.txt does not include it.\n"+
+			"\trun 'go mod tidy; go mod vendor' to sync", modRoot, m.Path, m.Version)
+	}
+	cfg.BuildMod = "vendor"
+}
+
 // Allowed reports whether module m is allowed (not excluded) by the main module's go.mod.
 func Allowed(m module.Version) bool {
 	return !excluded[m]

src/go.mod

@@ -7,5 +7,4 @@ require (
 	golang.org/x/net v0.0.0-20190424112056-4829fb13d2c6
 	golang.org/x/sys v0.0.0-20190425145619-16072639606e // indirect
 	golang.org/x/text v0.3.2 // indirect
-	golang.org/x/tools v0.0.0-20190425214124-2d660fb8a000 // indirect
 )

src/go.sum

-golang.org/x/crypto v0.0.0-20181025213731-e84da0312774 h1:a4tQYYYuK9QdeO/+kEvNYyuR21S+7ve5EANok6hABhI=
-golang.org/x/crypto v0.0.0-20181025213731-e84da0312774/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20190424203555-c05e17bb3b2d h1:adrbvkTDn9rGnXg2IJDKozEpXXLZN89pdIA+Syt4/u0=
 golang.org/x/crypto v0.0.0-20190424203555-c05e17bb3b2d/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
-golang.org/x/net v0.0.0-20181213202711-891ebc4b82d6 h1:gT0Y6H7hbVPUtvtk0YGxMXPgN+p8fYlqWkgJeUCZcaQ=
-golang.org/x/net v0.0.0-20181213202711-891ebc4b82d6/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
-golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190424112056-4829fb13d2c6 h1:FP8hkuE6yUEaJnK7O2eTuejKWwW+Rhfj80dQ2JcKxCU=
 golang.org/x/net v0.0.0-20190424112056-4829fb13d2c6/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
-golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20190306220234-b354f8bf4d9e h1:UndnRDGP/JcdZX1LBubo1fJ3Jt6GnKREteLJvysiiPE=
-golang.org/x/sys v0.0.0-20190306220234-b354f8bf4d9e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190425145619-16072639606e h1:4ktJgTV34+N3qOZUc5fAaG3Pb11qzMm3PkAoTAgUZ2I=
 golang.org/x/sys v0.0.0-20190425145619-16072639606e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/text v0.1.1-0.20171102144821-8253218a5ec6 h1:j8pkdn+8tJbBXIFRILFAB5MDo/hAZg4TnknVwnhU6bI=
-golang.org/x/text v0.1.1-0.20171102144821-8253218a5ec6/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2 h1:tW2bmiBqwgJj/UpqtC8EpXEZVYOwU0yG4iWbprSVAcs=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
-golang.org/x/tools v0.0.0-20190425214124-2d660fb8a000/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=

src/vendor/modules.txt

 # golang.org/x/crypto v0.0.0-20190424203555-c05e17bb3b2d
 golang.org/x/crypto/chacha20poly1305
 golang.org/x/crypto/cryptobyte
+golang.org/x/crypto/cryptobyte/asn1
 golang.org/x/crypto/curve25519
 golang.org/x/crypto/hkdf
-golang.org/x/crypto/cryptobyte/asn1
 golang.org/x/crypto/internal/chacha20
 golang.org/x/crypto/internal/subtle
 golang.org/x/crypto/poly1305
 # golang.org/x/net v0.0.0-20190424112056-4829fb13d2c6
 golang.org/x/net/dns/dnsmessage
-golang.org/x/net/lif
-golang.org/x/net/route
 golang.org/x/net/http/httpguts
 golang.org/x/net/http/httpproxy
 golang.org/x/net/http2/hpack
 golang.org/x/net/idna
+golang.org/x/net/lif
 golang.org/x/net/nettest
+golang.org/x/net/route
 # golang.org/x/sys v0.0.0-20190425145619-16072639606e
 golang.org/x/sys/cpu
 golang.org/x/sys/unix
 # golang.org/x/text v0.3.2
 golang.org/x/text/secure/bidirule
+golang.org/x/text/transform
 golang.org/x/text/unicode/bidi
 golang.org/x/text/unicode/norm
-golang.org/x/text/transform