cmd/go: drop support for binary-only packages

Fixes #28152

Change-Id: I98db923bdf8de7acf2df452313427bfea43b63c9
Reviewed-on: https://go-review.googlesource.com/c/go/+/165746
Run-TryBot: Jay Conrod <jayconrod@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/go_test.go

@@ -4206,9 +4206,9 @@ func TestBinaryOnlyPackages(t *testing.T) {
 
 		package p1
 	`)
-	tg.wantStale("p1", "missing or invalid binary-only package", "p1 is binary-only but has no binary, should be stale")
+	tg.wantStale("p1", "binary-only packages are no longer supported", "p1 is binary-only, and this message should always be printed")
 	tg.runFail("install", "p1")
-	tg.grepStderr("missing or invalid binary-only package", "did not report attempt to compile binary-only package")
+	tg.grepStderr("binary-only packages are no longer supported", "did not report attempt to compile binary-only package")
 
 	tg.tempFile("src/p1/p1.go", `
 		package p1
@@ -4234,48 +4234,13 @@ func TestBinaryOnlyPackages(t *testing.T) {
 		import _ "fmt"
 		func G()
 	`)
-	tg.wantNotStale("p1", "binary-only package", "should NOT want to rebuild p1 (first)")
-	tg.run("install", "-x", "p1") // no-op, up to date
-	tg.grepBothNot(`[\\/]compile`, "should not have run compiler")
-	tg.run("install", "p2") // does not rebuild p1 (or else p2 will fail)
-	tg.wantNotStale("p2", "", "should NOT want to rebuild p2")
-
-	// changes to the non-source-code do not matter,
-	// and only one file needs the special comment.
-	tg.tempFile("src/p1/missing2.go", `
-		package p1
-		func H()
-	`)
-	tg.wantNotStale("p1", "binary-only package", "should NOT want to rebuild p1 (second)")
-	tg.wantNotStale("p2", "", "should NOT want to rebuild p2")
-
-	tg.tempFile("src/p3/p3.go", `
-		package main
-		import (
-			"p1"
-			"p2"
-		)
-		func main() {
-			p1.F(false)
-			p2.F()
-		}
-	`)
-	tg.run("install", "p3")
-
-	tg.run("run", tg.path("src/p3/p3.go"))
-	tg.grepStdout("hello from p1", "did not see message from p1")
-
-	tg.tempFile("src/p4/p4.go", `package main`)
-	// The odd string split below avoids vet complaining about
-	// a // +build line appearing too late in this source file.
-	tg.tempFile("src/p4/p4not.go", `//go:binary-only-package
-
-		/`+`/ +build asdf
+	tg.wantStale("p1", "binary-only package", "should NOT want to rebuild p1 (first)")
+	tg.runFail("install", "p2")
+	tg.grepStderr("p1: binary-only packages are no longer supported", "did not report error for binary-only p1")
 
-		package main
-	`)
-	tg.run("list", "-f", "{{.BinaryOnly}}", "p4")
-	tg.grepStdout("false", "did not see BinaryOnly=false for p4")
+	tg.run("list", "-deps", "-f", "{{.ImportPath}}: {{.BinaryOnly}}", "p2")
+	tg.grepStdout("p1: true", "p1 not listed as BinaryOnly")
+	tg.grepStdout("p2: false", "p2 listed as BinaryOnly")
 }
 
 // Issue 16050.

src/cmd/go/internal/help/helpdoc.go

@@ -635,15 +635,6 @@ constraints, but the go command stops scanning for build constraints
 at the first item in the file that is not a blank line or //-style
 line comment. See the go/build package documentation for
 more details.
-
-Through the Go 1.12 release, non-test Go source files can also include
-a //go:binary-only-package comment, indicating that the package
-sources are included for documentation only and must not be used to
-build the package binary. This enables distribution of Go packages in
-their compiled form alone. Even binary-only packages require accurate
-import blocks listing required dependencies, so that those
-dependencies can be supplied when linking the resulting command.
-Note that this feature is scheduled to be removed after the Go 1.12 release.
 	`,
 }
 

src/cmd/go/internal/list/list.go

@@ -60,7 +60,7 @@ to -f '{{.ImportPath}}'. The struct being passed to the template is:
         StaleReason   string   // explanation for Stale==true
         Root          string   // Go root or Go path dir containing this package
         ConflictDir   string   // this directory shadows Dir in $GOPATH
-        BinaryOnly    bool     // binary-only package: cannot be recompiled from sources
+        BinaryOnly    bool     // binary-only package (no longer supported)
         ForTest       string   // package is only for use in named test
         Export        string   // file containing export data (when using -export)
         Module        *Module  // info about package's containing module, if any (can be nil)

src/cmd/go/internal/work/exec.go

@@ -422,24 +422,12 @@ func (b *Builder) build(a *Action) (err error) {
 	}
 
 	if a.Package.BinaryOnly {
-		_, err := os.Stat(a.Package.Target)
-		if err == nil {
-			a.built = a.Package.Target
-			a.Target = a.Package.Target
-			if b.NeedExport {
-				a.Package.Export = a.Package.Target
-			}
-			a.buildID = b.fileHash(a.Package.Target)
-			a.Package.Stale = false
-			a.Package.StaleReason = "binary-only package"
-			return nil
-		}
-		a.Package.Stale = true
-		a.Package.StaleReason = "missing or invalid binary-only package"
+		p.Stale = true
+		p.StaleReason = "binary-only packages are no longer supported"
 		if b.IsCmdList {
 			return nil
 		}
-		return fmt.Errorf("missing or invalid binary-only package; expected file %q", a.Package.Target)
+		return errors.New("binary-only packages are no longer supported")
 	}
 
 	if err := b.Mkdir(a.Objdir); err != nil {

src/go/build/doc.go

@@ -149,24 +149,28 @@
 //
 // Binary-Only Packages
 //
-// It is possible to distribute packages in binary form without including the
-// source code used for compiling the package. To do this, the package must
-// be distributed with a source file not excluded by build constraints and
-// containing a "//go:binary-only-package" comment.
-// Like a build constraint, this comment must appear near the top of the file,
-// preceded only by blank lines and other line comments and with a blank line
+// In Go 1.12 and earlier, it was possible to distribute packages in binary
+// form without including the source code used for compiling the package.
+// The package was distributed with a source file not excluded by build
+// constraints and containing a "//go:binary-only-package" comment. Like a
+// build constraint, this comment appeared at the top of a file, preceded
+// only by blank lines and other line comments and with a blank line
 // following the comment, to separate it from the package documentation.
 // Unlike build constraints, this comment is only recognized in non-test
 // Go source files.
 //
-// The minimal source code for a binary-only package is therefore:
+// The minimal source code for a binary-only package was therefore:
 //
 //	//go:binary-only-package
 //
 //	package mypkg
 //
-// The source code may include additional Go code. That code is never compiled
-// but will be processed by tools like godoc and might be useful as end-user
-// documentation.
+// The source code could include additional Go code. That code was never
+// compiled but would be processed by tools like godoc and might be useful
+// as end-user documentation.
+//
+// "go build" and other commands no longer support binary-only-packages.
+// Import and ImportDir will still set the BinaryOnly flag in packages
+// containing these comments for use in tools and error messages.
 //
 package build