cmd/go: annotate versions in vendor/modules.txt

In order to prevent edit wars with previous cmd/go releases,
the new version annotations are only included if the main module
specifies 'go 1.17' or higher.

Fixes #36876

Change-Id: Iba15e47dd1ac2c16d754679a9b501db4069fa250
Reviewed-on: https://go-review.googlesource.com/c/go/+/315409
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>

7 files changed, 154 insertions, 33 deletions

diff --git a/doc/go1.17.html b/doc/go1.17.html
index eab4e1eeeb..ef1472d90a 100644
--- a/doc/go1.17.html
+++ b/doc/go1.17.html
@@ -120,6 +120,16 @@ Do not send CLs removing the interior tags from such phrases.
   files.)
 </p>
 
+<h4 id="vendor-go-versions"><code>go</code> versions in <code>vendor/modules.txt</code></h4>
+
+<p><!-- golang.org/issue/36876 -->
+  If the main module specifies <code>go</code> <code>1.17</code> or higher,
+  <code>go</code> <code>mod</code> <code>vendor</code> now annotates
+  <code>vendor/modules.txt</code> with the <code>go</code> version indicated by
+  each vendored module in its own <code>go.mod</code> file. The annotated
+  version is used when building the module's packages from vendored source code.
+</p>
+
 <h2 id="runtime">Runtime</h2>
 
 <p>
diff --git a/src/cmd/go/internal/modcmd/vendor.go b/src/cmd/go/internal/modcmd/vendor.go
index 6ebc18dcd8..86eab89065 100644
--- a/src/cmd/go/internal/modcmd/vendor.go
+++ b/src/cmd/go/internal/modcmd/vendor.go
@@ -88,15 +88,23 @@ func runVendor(ctx context.Context, cmd *base.Command, args []string) {
 	}
 
 	includeAllReplacements := false
+	includeGoVersions := false
 	isExplicit := map[module.Version]bool{}
-	if gv := modload.ModFile().Go; gv != nil && semver.Compare("v"+gv.Version, "v1.14") >= 0 {
-		// If the Go version is at least 1.14, annotate all explicit 'require' and
-		// 'replace' targets found in the go.mod file so that we can perform a
-		// stronger consistency check when -mod=vendor is set.
-		for _, r := range modload.ModFile().Require {
-			isExplicit[r.Mod] = true
+	if gv := modload.ModFile().Go; gv != nil {
+		if semver.Compare("v"+gv.Version, "v1.14") >= 0 {
+			// If the Go version is at least 1.14, annotate all explicit 'require' and
+			// 'replace' targets found in the go.mod file so that we can perform a
+			// stronger consistency check when -mod=vendor is set.
+			for _, r := range modload.ModFile().Require {
+				isExplicit[r.Mod] = true
+			}
+			includeAllReplacements = true
+		}
+		if semver.Compare("v"+gv.Version, "v1.17") >= 0 {
+			// If the Go version is at least 1.17, annotate all modules with their
+			// 'go' version directives.
+			includeGoVersions = true
 		}
-		includeAllReplacements = true
 	}
 
 	var vendorMods []module.Version
@@ -110,26 +118,35 @@ func runVendor(ctx context.Context, cmd *base.Command, args []string) {
 	}
 	module.Sort(vendorMods)
 
-	var buf bytes.Buffer
+	var (
+		buf bytes.Buffer
+		w   io.Writer = &buf
+	)
+	if cfg.BuildV {
+		w = io.MultiWriter(&buf, os.Stderr)
+	}
+
 	for _, m := range vendorMods {
 		line := moduleLine(m, modload.Replacement(m))
-		buf.WriteString(line)
-		if cfg.BuildV {
-			os.Stderr.WriteString(line)
+		io.WriteString(w, line)
+
+		goVersion := ""
+		if includeGoVersions {
+			goVersion = modload.ModuleInfo(ctx, m.Path).GoVersion
 		}
-		if isExplicit[m] {
-			buf.WriteString("## explicit\n")
-			if cfg.BuildV {
-				os.Stderr.WriteString("## explicit\n")
-			}
+		switch {
+		case isExplicit[m] && goVersion != "":
+			fmt.Fprintf(w, "## explicit; go %s\n", goVersion)
+		case isExplicit[m]:
+			io.WriteString(w, "## explicit\n")
+		case goVersion != "":
+			fmt.Fprintf(w, "## go %s\n", goVersion)
 		}
+
 		pkgs := modpkgs[m]
 		sort.Strings(pkgs)
 		for _, pkg := range pkgs {
-			fmt.Fprintf(&buf, "%s\n", pkg)
-			if cfg.BuildV {
-				fmt.Fprintf(os.Stderr, "%s\n", pkg)
-			}
+			fmt.Fprintf(w, "%s\n", pkg)
 			vendorPkg(vdir, pkg)
 		}
 	}
diff --git a/src/cmd/go/internal/modload/vendor.go b/src/cmd/go/internal/modload/vendor.go
index d8fd91f1fe..80713b0812 100644
--- a/src/cmd/go/internal/modload/vendor.go
+++ b/src/cmd/go/internal/modload/vendor.go
@@ -31,6 +31,7 @@ var (
 type vendorMetadata struct {
 	Explicit    bool
 	Replacement module.Version
+	GoVersion   string
 }
 
 // readVendorList reads the list of vendored modules from vendor/modules.txt.
@@ -104,6 +105,10 @@ func readVendorList() {
 					if entry == "explicit" {
 						meta.Explicit = true
 					}
+					if strings.HasPrefix(entry, "go ") {
+						meta.GoVersion = strings.TrimPrefix(entry, "go ")
+						rawGoVersion.Store(mod, meta.GoVersion)
+					}
 					// All other tokens are reserved for future use.
 				}
 				vendorMeta[mod] = meta
diff --git a/src/cmd/go/testdata/script/mod_go_version_vendor.txt b/src/cmd/go/testdata/script/mod_go_version_vendor.txt
index 05be54886f..6364e17daa 100644
--- a/src/cmd/go/testdata/script/mod_go_version_vendor.txt
+++ b/src/cmd/go/testdata/script/mod_go_version_vendor.txt
@@ -4,7 +4,6 @@
 
 [short] skip
 
-go mod init example.com/foo
 go mod edit -replace=example.com/use113@v0.1.0=./use113
 
 go mod vendor
@@ -20,7 +19,10 @@ go mod vendor
 ! grep 1.13 vendor/modules.txt
 go build .
 
+-- go.mod --
+module example.com/foo
 
+go 1.16
 -- foo.go --
 package foo
 
diff --git a/src/cmd/go/testdata/script/mod_vendor_goversion.txt b/src/cmd/go/testdata/script/mod_vendor_goversion.txt
new file mode 100644
index 0000000000..7bc67ef30f
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_vendor_goversion.txt
@@ -0,0 +1,87 @@
+# https://golang.org/issue/36876: As of Go 1.17, vendor/modules.txt should
+# indicate the language version used by each dependency.
+
+[short] skip
+
+
+# Control case: without a vendor directory, need117 builds and bad114 doesn't.
+
+go build example.net/need117
+! go build example.net/bad114
+stderr '^bad114[/\\]bad114.go:15:2: duplicate method Y$'
+
+
+# With a vendor/modules.txt lacking language versions, the world is topsy-turvy.
+# Things that ought to build shouldn't, and things that shouldn't build do.
+
+go mod vendor
+go build example.net/bad114
+! go build example.net/need117
+stderr '^vendor[/\\]example\.net[/\\]need117[/\\]need117.go:5:18: .*\n\tconversion of slices to array pointers only supported as of -lang=go1\.17'
+
+
+# Upgrading the main module to 1.17 adds version annotations.
+# Then everything is once again consistent with the non-vendored world.
+
+go mod edit -go=1.17
+go mod vendor
+go build example.net/need117
+! go build example.net/bad114
+stderr '^vendor[/\\]example\.net[/\\]bad114[/\\]bad114.go:15:2: duplicate method Y$'
+
+
+-- go.mod --
+module example.net/m
+
+go 1.16
+
+require (
+	example.net/bad114 v0.1.0
+	example.net/need117 v0.1.0
+)
+
+replace (
+	example.net/bad114 v0.1.0 => ./bad114
+	example.net/need117 v0.1.0 => ./need117
+)
+-- m.go --
+package m
+
+import _ "example.net/bad114"
+import _ "example.net/need117"
+
+-- bad114/go.mod --
+// Module bad114 requires Go 1.14 or higher, but declares Go 1.13.
+module example.net/bad114
+
+go 1.13
+-- bad114/bad114.go --
+package bad114
+
+type XY interface {
+	X()
+	Y()
+}
+
+type YZ interface {
+	Y()
+	Z()
+}
+
+type XYZ interface {
+	XY
+	YZ
+}
+
+-- need117/go.mod --
+// Module need117 requires Go 1.17 or higher.
+module example.net/need117
+
+go 1.17
+-- need117/need117.go --
+package need117
+
+func init() {
+		 s := make([]byte, 4)
+		 _ = (*[4]byte)(s)
+}
diff --git a/src/cmd/vendor/modules.txt b/src/cmd/vendor/modules.txt
index 0457b374b0..69d10d074a 100644
--- a/src/cmd/vendor/modules.txt
+++ b/src/cmd/vendor/modules.txt
@@ -1,5 +1,5 @@
 # github.com/google/pprof v0.0.0-20210226084205-cbba55b83ad5
-## explicit
+## explicit; go 1.14
 github.com/google/pprof/driver
 github.com/google/pprof/internal/binutils
 github.com/google/pprof/internal/driver
@@ -19,17 +19,17 @@ github.com/google/pprof/third_party/svgpan
 ## explicit
 github.com/ianlancetaylor/demangle
 # golang.org/x/arch v0.0.0-20210308155006-05f8f0431f72
-## explicit
+## explicit; go 1.11
 golang.org/x/arch/arm/armasm
 golang.org/x/arch/arm64/arm64asm
 golang.org/x/arch/ppc64/ppc64asm
 golang.org/x/arch/x86/x86asm
 # golang.org/x/crypto v0.0.0-20210220033148-5ea612d1eb83
-## explicit
+## explicit; go 1.11
 golang.org/x/crypto/ed25519
 golang.org/x/crypto/ed25519/internal/edwards25519
 # golang.org/x/mod v0.4.3-0.20210409134425-858fdbee9c24
-## explicit
+## explicit; go 1.12
 golang.org/x/mod/internal/lazyregexp
 golang.org/x/mod/modfile
 golang.org/x/mod/module
@@ -40,16 +40,16 @@ golang.org/x/mod/sumdb/note
 golang.org/x/mod/sumdb/tlog
 golang.org/x/mod/zip
 # golang.org/x/sys v0.0.0-20210403161142-5e06dd20ab57
-## explicit
+## explicit; go 1.12
 golang.org/x/sys/internal/unsafeheader
 golang.org/x/sys/plan9
 golang.org/x/sys/unix
 golang.org/x/sys/windows
 # golang.org/x/term v0.0.0-20210220032956-6a3ed077a48d
-## explicit
+## explicit; go 1.11
 golang.org/x/term
 # golang.org/x/tools v0.1.1-0.20210422170518-f946a157eefe
-## explicit
+## explicit; go 1.12
 golang.org/x/tools/cover
 golang.org/x/tools/go/analysis
 golang.org/x/tools/go/analysis/internal/analysisflags
@@ -93,6 +93,6 @@ golang.org/x/tools/go/types/typeutil
 golang.org/x/tools/internal/analysisinternal
 golang.org/x/tools/internal/lsp/fuzzy
 # golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1
-## explicit
+## explicit; go 1.11
 golang.org/x/xerrors
 golang.org/x/xerrors/internal
diff --git a/src/vendor/modules.txt b/src/vendor/modules.txt
index 499e6fc3fa..d849d6553c 100644
--- a/src/vendor/modules.txt
+++ b/src/vendor/modules.txt
@@ -1,5 +1,5 @@
 # golang.org/x/crypto v0.0.0-20210220033148-5ea612d1eb83
-## explicit
+## explicit; go 1.11
 golang.org/x/crypto/chacha20
 golang.org/x/crypto/chacha20poly1305
 golang.org/x/crypto/cryptobyte
@@ -9,7 +9,7 @@ golang.org/x/crypto/hkdf
 golang.org/x/crypto/internal/subtle
 golang.org/x/crypto/poly1305
 # golang.org/x/net v0.0.0-20210405180319-a5a99cb37ef4
-## explicit
+## explicit; go 1.11
 golang.org/x/net/dns/dnsmessage
 golang.org/x/net/http/httpguts
 golang.org/x/net/http/httpproxy
@@ -19,10 +19,10 @@ golang.org/x/net/lif
 golang.org/x/net/nettest
 golang.org/x/net/route
 # golang.org/x/sys v0.0.0-20210403161142-5e06dd20ab57
-## explicit
+## explicit; go 1.12
 golang.org/x/sys/cpu
 # golang.org/x/text v0.3.6-0.20210227105805-e3aa4adf54f6
-## explicit
+## explicit; go 1.11
 golang.org/x/text/secure/bidirule
 golang.org/x/text/transform
 golang.org/x/text/unicode/bidi