Merge pull request 'Run the slow test packages in shards and build judges from a warm Go cache (hq issue 717)' (#334) from fix/717-the-suite-runs-in-under-two-minutes into main

internal/builder/release_branch_test.go

@@ -156,6 +156,9 @@ run)
   if [ "$1" = go ] && [ "$2" = test ] && [ -n "$REPLAYS" ]; then
     echo "HOME=$HOME GOCACHE=$GOCACHE GOMODCACHE=$GOMODCACHE GOENV=$GOENV GOFLAGS=$GOFLAGS DIR=$workdir" >> "$REPLAYS"
   fi
+  if [ "$1" = go ] && [ -n "$WARM_GO_CACHE" ] && [ -n "$GOCACHE" ] && [ -z "$(ls -A "$GOCACHE" 2>/dev/null)" ]; then
+    mkdir -p "$GOCACHE" && cp -R "$WARM_GO_CACHE/." "$GOCACHE/"
+  fi
   cd "$workdir" && exec "$@" ;;
 esac
 exit 1
@@ -165,6 +168,8 @@ exit 1
 	}
 	t.Setenv("PATH", dir+string(os.PathListSeparator)+os.Getenv("PATH"))
 	t.Setenv("GOTOOLCHAIN", "local")
+	// An empty Go cache the check names is filled from a warm one before `go` runs (warm_go_cache_test.go).
+	t.Setenv("WARM_GO_CACHE", warmGoCache(t))
 	return built
 }
 
@@ -566,6 +571,8 @@ func TestTheBuildSeatNeverReadsMeshLabAtAReleaseBranch(t *testing.T) {
 // a temporary directory of the host; and no container a check runs for the pull request mounts the judge cache.
 func TestJudgesAreBuiltWarmFromAJudgeCacheNoCheckContainerMounts(t *testing.T) {
 	built := aRuntimeThatBuildsTheJudge(t)
+	// Not filled from the test's warm cache: what the first judge's build leaves in the judge cache is what is proved.
+	t.Setenv("WARM_GO_CACHE", "")
 	runs := filepath.Join(t.TempDir(), "runs")
 	t.Setenv("RUNS", runs)
 	tmp := t.TempDir()

internal/builder/warm_go_cache_test.go

@@ -0,0 +1,80 @@
+package builder
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"sync"
+	"testing"
+)
+
+// **A judge's build in a test starts from a warm Go cache** (novox/hq issue 717). The runtime these tests put on
+// PATH (aRuntimeThatBuildsTheJudge) runs the check's `go build` and `go test` on this machine with the Go cache the
+// check names — a fresh directory in every test — so each of them compiled the standard library from nothing: some
+// ten CPU-seconds a build, under twenty tests, half of the CPU the whole suite spent. The runtime now fills an empty
+// Go cache it is given from one this process warmed once, before it runs `go`; what the check names, mounts and
+// keeps is unchanged, and so is what each test reads of it. A cache entry is keyed by everything the compile
+// depends on, flags included, so a build with a planted -toolexec hook still misses it and still runs its hook.
+//
+// The warm cache lives beside the system's temporary directory as it was when the package started, never under a
+// TMPDIR a test set and then asserts left empty, and is removed when the package's tests end.
+var (
+	warmCacheBase = os.TempDir()
+	warmCacheOnce sync.Once
+	warmCacheDir  string
+)
+
+func TestMain(m *testing.M) {
+	code := m.Run()
+	if warmCacheDir != "" {
+		_ = os.RemoveAll(warmCacheDir)
+	}
+	os.Exit(code)
+}
+
+// warmGoCache is a Go cache holding what a judge's build and the replays' `go test` compile of the standard
+// library, or "" when it cannot be warmed — a test then builds cold, as before, and is only slower.
+func warmGoCache(t *testing.T) string {
+	t.Helper()
+	warmCacheOnce.Do(func() {
+		dir, err := os.MkdirTemp(warmCacheBase, "judge-warm-go-cache-")
+		if err != nil {
+			return
+		}
+		src := filepath.Join(dir, "src")
+		files := map[string]string{
+			"go.mod":       "module example.org/warm\n\ngo 1.22\n",
+			"main.go":      "package main\n\nimport (\n\t\"fmt\"\n\t\"os\"\n)\n\nfunc main() { fmt.Fprintln(os.Stdout, len(os.Args)) }\n",
+			"main_test.go": "package main\n\nimport \"testing\"\n\nfunc TestWarm(t *testing.T) {}\n",
+		}
+		for name, body := range files {
+			if err := os.MkdirAll(src, 0o755); err != nil {
+				return
+			}
+			if err := os.WriteFile(filepath.Join(src, name), []byte(body), 0o644); err != nil {
+				return
+			}
+		}
+		cache := filepath.Join(dir, "go-cache")
+		env := append(os.Environ(), "GOCACHE="+cache, "GOENV=off", "GOTOOLCHAIN=local", "GOPROXY=off", "GOWORK=off",
+			"GOFLAGS=-buildvcs=false", "TMPDIR="+warmCacheBase)
+		// As the check builds a judge (CGO off) and runs the replays (CGO as the toolchain has it).
+		for _, run := range [][]string{
+			{"env", "CGO_ENABLED=0", "go", "build", "-o", filepath.Join(dir, "judge"), "."},
+			{"go", "test", "-count=1", "."},
+		} {
+			cmd := exec.Command(run[0], run[1:]...)
+			cmd.Dir, cmd.Env = src, env
+			if out, err := cmd.CombinedOutput(); err != nil {
+				t.Logf("the warm Go cache could not be built, so judges build cold: %v\n%s", err, out)
+				_ = os.RemoveAll(dir)
+				return
+			}
+		}
+		warmCacheDir = dir
+	})
+	if warmCacheDir == "" {
+		return ""
+	}
+	return filepath.Join(warmCacheDir, "go-cache")
+}