From cb27fed361a2effcc438ccf218b110d6a5489245 Mon Sep 17 00:00:00 2001
From: Ivan Trubach <mr.trubach@icloud.com>
Date: Sun, 24 May 2020 14:15:26 +0300
Subject: [PATCH] Do not rebuild gotip if the HEAD does not change
On successful build a sentinel zero-byte file is written,
similar to .unpacked-success in internal/version. If such
file exists on next gotip download, compare HEADs before
and after FETCH_HEAD checkout, and trigger the build iff
they differ. In that case, sentinel file is removed to
make git clean happy and indicate that rebuild is needed.
---
gotip/main.go | 40 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 39 insertions(+), 1 deletion(-)
diff --git a/gotip/main.go b/gotip/main.go
index d1c69cc7..81bf2407 100644
--- a/gotip/main.go
+++ b/gotip/main.go
@@ -16,8 +16,10 @@
package main
import (
+ "bytes"
"errors"
"fmt"
+ "io/ioutil"
"log"
"os"
"os/exec"
@@ -95,6 +97,9 @@ func installTip(root, clNumber string) error {
cmd.Dir = root
return cmd.Output()
}
+ chomp := func(s []byte) []byte {
+ return bytes.TrimRight(s, " \t\r\n")
+ }
if _, err := os.Stat(filepath.Join(root, ".git")); err != nil {
if err := os.MkdirAll(root, 0755); err != nil {
@@ -105,6 +110,16 @@ func installTip(root, clNumber string) error {
}
}
+ // Get current HEAD if there is an existing build.
+ var oldHead []byte
+ if _, err := os.Stat(filepath.Join(root, builtOkay)); err == nil {
+ head, err := gitOutput("rev-parse", "--short", "HEAD")
+ if err != nil {
+ return fmt.Errorf("failed to parse old HEAD revision: %v", err)
+ }
+ oldHead = head
+ }
+
if clNumber != "" {
fmt.Fprintf(os.Stderr, "This will download and execute code from golang.org/cl/%s, continue? [y/n] ", clNumber)
var answer string
@@ -152,6 +167,23 @@ func installTip(root, clNumber string) error {
if err := git("-c", "advice.detachedHead=false", "checkout", "FETCH_HEAD"); err != nil {
return fmt.Errorf("failed to checkout git repository: %v", err)
}
+
+ // Compare old and new HEADs to avoid unnecessary rebuilds if there are no changes.
+ // Notice that oldHead is not nil iff the last build was successful.
+ if oldHead != nil {
+ newHead, err := gitOutput("rev-parse", "--short", "HEAD")
+ if err != nil {
+ return fmt.Errorf("failed to parse new HEAD revision: %v", err)
+ }
+ if bytes.Equal(oldHead, newHead) {
+ log.Printf("Already built %s in %v", chomp(newHead), root)
+ return nil
+ }
+ if err := os.Remove(filepath.Join(root, builtOkay)); err != nil {
+ return err
+ }
+ }
+
// It shouldn't be the case, but in practice sometimes binary artifacts
// generated by earlier Go versions interfere with the build.
//
@@ -181,7 +213,9 @@ func installTip(root, clNumber string) error {
if err := cmd.Run(); err != nil {
return fmt.Errorf("failed to build go: %v", err)
}
-
+ if err := ioutil.WriteFile(filepath.Join(root, builtOkay), nil, 0644); err != nil {
+ return err
+ }
return nil
}
@@ -198,6 +232,10 @@ func makeScript() string {
const caseInsensitiveEnv = runtime.GOOS == "windows"
+// builtOkay is a sentinel zero-byte file to indicate that Go
+// repository was cloned and built successfully.
+const builtOkay = ".built-success"
+
func exe() string {
if runtime.GOOS == "windows" {
return ".exe"