cmd/doc: flag usage() inconsistency

Inconsistency between cmd/doc/main.go and cmd/go/internal/doc/doc.go

Fixes #34976

Change-Id: I429200f9305d473edb4505216bb4840ba92af818
Reviewed-on: https://go-review.googlesource.com/c/go/+/201857
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/doc/main.go

@@ -65,9 +65,10 @@ func usage() {
 	fmt.Fprintf(os.Stderr, "Usage of [go] doc:\n")
 	fmt.Fprintf(os.Stderr, "\tgo doc\n")
 	fmt.Fprintf(os.Stderr, "\tgo doc <pkg>\n")
-	fmt.Fprintf(os.Stderr, "\tgo doc <sym>[.<method>]\n")
-	fmt.Fprintf(os.Stderr, "\tgo doc [<pkg>].<sym>[.<method>]\n")
-	fmt.Fprintf(os.Stderr, "\tgo doc <pkg> <sym>[.<method>]\n")
+	fmt.Fprintf(os.Stderr, "\tgo doc <sym>[.<methodOrField>]\n")
+	fmt.Fprintf(os.Stderr, "\tgo doc [<pkg>.]<sym>[.<methodOrField>]\n")
+	fmt.Fprintf(os.Stderr, "\tgo doc [<pkg>.][<sym>.]<methodOrField>\n")
+	fmt.Fprintf(os.Stderr, "\tgo doc <pkg> <sym>[.<methodOrField>]\n")
 	fmt.Fprintf(os.Stderr, "For more information run\n")
 	fmt.Fprintf(os.Stderr, "\tgo help doc\n\n")
 	fmt.Fprintf(os.Stderr, "Flags:\n")

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

+# go doc --help
+! go doc --help
+stderr 'go doc'
+stderr 'go doc <pkg>'
+stderr 'go doc <sym>\[\.<methodOrField>\]'
+stderr 'go doc \[<pkg>\.\]<sym>\[\.<methodOrField>\]'
+stderr 'go doc \[<pkg>\.\]\[<sym>\.\]<methodOrField>'
+stderr 'go doc <pkg> <sym>\[\.<methodOrField>\]'
+
+# go help doc
+go help doc
+stdout 'go doc'
+stdout 'go doc <pkg>'
+stdout 'go doc <sym>\[\.<methodOrField>\]'
+stdout 'go doc \[<pkg>\.\]<sym>\[\.<methodOrField>\]'
+stdout 'go doc \[<pkg>\.\]\[<sym>\.\]<methodOrField>'
+stdout 'go doc <pkg> <sym>\[\.<methodOrField>\]'
+
+# go doc <pkg>
+go doc p/v2
+stdout .
+
+# go doc <pkg> <sym>
+go doc p/v2 Symbol
+stdout .
+
+# go doc <pkg> <sym> <method>
+! go doc p/v2 Symbol Method
+stderr .
+
+# go doc <pkg>.<sym>
+go doc p/v2.Symbol
+stdout .
+
+# go doc <pkg>.<sym>.<method>
+go doc p/v2.Symbol.Method
+stdout .
+
+# go doc <sym>
+go doc Symbol
+stdout .
+
+# go doc <sym> <method>
+! go doc Symbol Method
+stderr .
+
+# go doc <sym>.<method>
+go doc Symbol.Method
+stdout .
+
+# go doc <pkg>.<method>
+go doc p/v2.Method
+stdout .
+
+# go doc <pkg> <method>
+go doc p/v2 Method
+stdout .
+
+# go doc <method>
+go doc Method
+stdout .
+
+-- go.mod --
+module p/v2
+
+go 1.13
+
+-- p.go --
+package p
+
+type Symbol struct{}
+
+func (Symbol) Method() error {
+	return nil
+}