go: build/install godoc & vet

Bottles and installs `godoc` and `go vet` unless requested otherwise.

Closes #37133

Past references:

1) #23281
2) #25210

Closes #37159.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Formula/go.rb

@@ -18,10 +18,17 @@ class Go < Formula
   option "with-cc-all", "Build with cross-compilers and runtime support for all supported platforms"
   option "with-cc-common", "Build with cross-compilers and runtime support for darwin, linux and windows"
   option "without-cgo", "Build without cgo"
+  option "without-godoc", "godoc will not be installed for you"
+  option "without-vet", "vet will not be installed for you"
 
   deprecated_option "cross-compile-all" => "with-cc-all"
   deprecated_option "cross-compile-common" => "with-cc-common"
 
+  resource "gotools" do
+    url "https://go.googlesource.com/tools.git",
+    :revision => "69db398fe0e69396984e3967724820c1f631e971"
+  end
+
   def install
     # host platform (darwin) must come last in the targets list
     if build.with? "cc-all"
@@ -64,21 +71,35 @@ def install
     end
 
     (buildpath/"pkg/obj").rmtree
-
     libexec.install Dir["*"]
     bin.install_symlink Dir["#{libexec}/bin/go*"]
+
+    if build.with?("godoc") || build.with?("vet")
+      ENV.prepend_path "PATH", bin
+      ENV["GOPATH"] = buildpath
+      (buildpath/"src/golang.org/x/tools").install resource("gotools")
+
+      if build.with? "godoc"
+        cd "src/golang.org/x/tools/cmd/godoc/" do
+          system "go", "build"
+          (libexec/"bin").install "godoc"
+        end
+        bin.install_symlink libexec/"bin/godoc"
+      end
+
+      if build.with? "vet"
+        cd "src/golang.org/x/tools/cmd/vet/" do
+          system "go", "build"
+          # This is where Go puts vet natively; not in the bin.
+          (libexec/"pkg/tool/darwin_amd64/").install "vet"
+        end
+      end
+    end
   end
 
   def caveats; <<-EOS.undent
     As of go 1.2, a valid GOPATH is required to use the `go get` command:
-      http://golang.org/doc/code.html#GOPATH
-
-    `go vet` and `go doc` are now part of the go.tools sub repo:
-      http://golang.org/doc/go1.2#go_tools_godoc
-
-    To get `go vet` and `go doc` run:
-      go get golang.org/x/tools/cmd/vet
-      go get golang.org/x/tools/cmd/godoc
+      https://golang.org/doc/code.html#GOPATH
 
     You may wish to add the GOROOT-based install location to your PATH:
       export PATH=$PATH:#{opt_libexec}/bin
@@ -99,5 +120,14 @@ def caveats; <<-EOS.undent
     # This is a a bare minimum of go working as it uses fmt, build, and run.
     system "#{bin}/go", "fmt", "hello.go"
     assert_equal "Hello World\n", `#{bin}/go run hello.go`
+
+    if build.with? "godoc"
+      assert File.exist?(libexec/"bin/godoc")
+      assert File.executable?(libexec/"bin/godoc")
+    end
+    if build.with? "vet"
+      assert File.exist?(libexec/"pkg/tool/darwin_amd64/vet")
+      assert File.executable?(libexec/"pkg/tool/darwin_amd64/vet")
+    end
   end
 end