cmd/go/internal/doc: reject meta packages in go doc

Meta-package names such as std, cmd, tool, work, and all are package
patterns that expand to multiple packages, not single documentable
packages. Today go doc std can fall through package resolution and print
documentation for an unrelated first match such as archive/tar.

Reject these names when they are the first argument to go doc, including
the two-argument form such as go doc std Foo. Keep go doc -http std
routing to the standard library page.

Fixes #53446

Change-Id: Iaf76b2be6fec0efa6f601b7959f4bcaac7ab776d

Author: raffr85

src/cmd/go/internal/doc/doc.go

@@ -233,12 +233,18 @@ func do(ctx context.Context, writer io.Writer, flagSet *flag.FlagSet, args []str
 			// Outside a module or workspace, go to the documentation for the standard library.
 			return doPkgsite(ctx, "std", "")
 		}
+		if args := flagSet.Args(); len(args) == 1 && args[0] == "std" {
+			return doPkgsite(ctx, "std", "")
+		}
 
 		// If args are provided, we need to figure out which page to open on the pkgsite
 		// instance. Run the logic below to determine a match for a symbol, method,
 		// or field, but don't actually print the documentation to the output.
 		writer = io.Discard
 	}
+	if a := flagSet.Args(); len(a) > 0 && search.IsMetaPackage(a[0]) {
+		return fmt.Errorf("no such package: %s", a[0])
+	}
 	var paths []string
 	var symbol, method string
 	// Loop until something is printed.

src/cmd/go/internal/doc/doc_test.go

@@ -1239,6 +1239,31 @@ func TestNoPackageClauseWhenNoMatch(t *testing.T) {
 	}
 }
 
+func TestMetaPackage(t *testing.T) {
+	maybeSkip(t)
+	for _, args := range [][]string{
+		{"std"},
+		{"cmd"},
+		{"all"},
+		{"tool"},
+		{"work"},
+		{"std", "Foo"},
+	} {
+		var b strings.Builder
+		var flagSet flag.FlagSet
+		err := do(t.Context(), &b, &flagSet, args)
+		if err == nil {
+			t.Fatalf("expected error for go doc %s; got output:\n%s", strings.Join(args, " "), b.String())
+		}
+		if want := "no such package: " + args[0]; !strings.Contains(err.Error(), want) {
+			t.Fatalf("unexpected error for go doc %s: %v", strings.Join(args, " "), err)
+		}
+		if strings.Contains(b.String(), `package tar // import "archive/tar"`) {
+			t.Fatalf("go doc %s resolved to archive/tar:\n%s", strings.Join(args, " "), b.String())
+		}
+	}
+}
+
 type trimTest struct {
 	path   string
 	prefix string

src/cmd/go/testdata/script/doc.txt

@@ -60,6 +60,22 @@ stdout .
 go doc Method
 stdout .
 
+# Meta packages are package patterns, not documentable packages.
+# Regression test for golang.org/issue/53446.
+! go doc std
+stderr '^doc: no such package: std$'
+! stdout 'package tar // import "archive/tar"'
+
+! go doc all
+stderr '^doc: no such package: all$'
+
+! go doc std Foo
+stderr '^doc: no such package: std$'
+
+env TEST_GODOC_URL_FILE=$WORK/url.txt
+go doc -http std
+grep '/std' $TEST_GODOC_URL_FILE
+
 -- go.mod --
 module p/v2