Enhance bootstrap stage selection

This simplifies the bootstrap process while making it more flexible by
moving the stage selection into a go binary(choosestage). It will now be
possible to have more than two build stages.

Now each stage has a ninja template(main.ninja.in) and a timestamp
file(main.ninja.in.timestamp). The timestamp file may be updated by any
build stage that wishes to regenerate the ninja template. If the
choosestage binaries sees that the timestamp is newer than the template,
it will choose the prior stage.

The main stage no longer writes to the source tree to update the
build.ninja.in file. This was a problem for read-only source trees.
Instead, the choosestage binary first checks to see if that file is
newer than the last bootstrap.ninja.in, copies it in place, and starts
the boostrap stage.

The bootstrap stage regenerates it's own ninja template, but that
required a loop through the main stage to actually run it. The
choosestage binary now detects if the template has changed for the
current stage, and will restart the stage.

One change is that if dependencies do get messed up, instead of silently
failing, there's a higher chance that the bootstrap step will just
continue looping, doing nothing. This can happen if the main stage
has a dependency that triggers the bootstrap stage, but the bootstrap
stage doesn't see anything required to rebuild the main ninja file. A
side effect of this requirement is that changes to test code will now
rebuild the main ninja file.

Change-Id: I9965cfba79dc0dbbd3af05f5944f7653054455a2

1 files changed, 30 insertions, 40 deletions

diff --git a/bootstrap/command.go b/bootstrap/command.go
index 932cfd7..4fb9c51 100644
--- a/bootstrap/command.go
+++ b/bootstrap/command.go
@@ -29,19 +29,21 @@ import (
 )
 
 var (
-	outFile      string
-	depFile      string
-	checkFile    string
-	manifestFile string
-	docFile      string
-	cpuprofile   string
-	runGoTests   bool
+	outFile          string
+	depFile          string
+	timestampFile    string
+	timestampDepFile string
+	manifestFile     string
+	docFile          string
+	cpuprofile       string
+	runGoTests       bool
 )
 
 func init() {
 	flag.StringVar(&outFile, "o", "build.ninja.in", "the Ninja file to output")
 	flag.StringVar(&depFile, "d", "", "the dependency file to output")
-	flag.StringVar(&checkFile, "c", "", "the existing file to check against")
+	flag.StringVar(&timestampFile, "timestamp", "", "file to write before the output file")
+	flag.StringVar(&timestampDepFile, "timestampdep", "", "the dependency file for the timestamp file")
 	flag.StringVar(&manifestFile, "m", "", "the bootstrap manifest file")
 	flag.StringVar(&docFile, "docs", "", "build documentation file to output")
 	flag.StringVar(&cpuprofile, "cpuprofile", "", "write cpu profile to file")
@@ -69,13 +71,15 @@ func Main(ctx *blueprint.Context, config interface{}, extraNinjaFileDeps ...stri
 		fatalf("no Blueprints file specified")
 	}
 
-	generatingBootstrapper := false
+	stage := StageMain
 	if c, ok := config.(ConfigInterface); ok {
-		generatingBootstrapper = c.GeneratingBootstrapper()
+		if c.GeneratingBootstrapper() {
+			stage = StageBootstrap
+		}
 	}
 
 	bootstrapConfig := &Config{
-		generatingBootstrapper: generatingBootstrapper,
+		stage: stage,
 		topLevelBlueprintsFile: flag.Arg(0),
 		runGoTests:             runGoTests,
 	}
@@ -118,48 +122,34 @@ func Main(ctx *blueprint.Context, config interface{}, extraNinjaFileDeps ...stri
 	}
 
 	const outFilePermissions = 0666
-	err = ioutil.WriteFile(outFile, buf.Bytes(), outFilePermissions)
-	if err != nil {
-		fatalf("error writing %s: %s", outFile, err)
-	}
-
-	if checkFile != "" {
-		checkData, err := ioutil.ReadFile(checkFile)
+	if timestampFile != "" {
+		err := ioutil.WriteFile(timestampFile, []byte{}, outFilePermissions)
 		if err != nil {
-			fatalf("error reading %s: %s", checkFile, err)
+			fatalf("error writing %s: %s", timestampFile, err)
 		}
 
-		matches := buf.Len() == len(checkData)
-		if matches {
-			for i, value := range buf.Bytes() {
-				if value != checkData[i] {
-					matches = false
-					break
-				}
-			}
-		}
-
-		if matches {
-			// The new file content matches the check-file content, so we set
-			// the new file's mtime and atime to match that of the check-file.
-			checkFileInfo, err := os.Stat(checkFile)
-			if err != nil {
-				fatalf("error stat'ing %s: %s", checkFile, err)
-			}
-
-			time := checkFileInfo.ModTime()
-			err = os.Chtimes(outFile, time, time)
+		if timestampDepFile != "" {
+			err := deptools.WriteDepFile(timestampDepFile, timestampFile, deps)
 			if err != nil {
-				fatalf("error setting timestamps for %s: %s", outFile, err)
+				fatalf("error writing depfile: %s", err)
 			}
 		}
 	}
 
+	err = ioutil.WriteFile(outFile, buf.Bytes(), outFilePermissions)
+	if err != nil {
+		fatalf("error writing %s: %s", outFile, err)
+	}
+
 	if depFile != "" {
 		err := deptools.WriteDepFile(depFile, outFile, deps)
 		if err != nil {
 			fatalf("error writing depfile: %s", err)
 		}
+		err = deptools.WriteDepFile(depFile+".timestamp", outFile+".timestamp", deps)
+		if err != nil {
+			fatalf("error writing depfile: %s", err)
+		}
 	}
 
 	srcDir := filepath.Dir(bootstrapConfig.topLevelBlueprintsFile)