Fix some problems with soong metrics loading

If we didn't need to run soong_build during the current run, we still
try to load the soong metrics. But in the case of `dist`, that's in a
directory that is not guaranteed to persist between runs.

Make loading the soong metrics optional if the file does not exist. Also
fixes a variable shadowing issue that meant we never passed it into
ctx.Metrics.

Test: treehugger
Change-Id: Ic836282f4d13e91daa0e7241ad7c488de3293d8b
(cherry picked from commit de3604453f)
Merged-In: Ic836282f4d13e91daa0e7241ad7c488de3293d8b

ui/build/soong.go

@@ -15,7 +15,9 @@
 package build
 
 import (
+	"errors"
 	"fmt"
+	"io/fs"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -491,10 +493,14 @@ func runSoong(ctx Context, config Config) {
 
 	ninja("bootstrap", "bootstrap.ninja", targets...)
 
-	var soongBuildMetrics *soong_metrics_proto.SoongBuildMetrics
 	if shouldCollectBuildSoongMetrics(config) {
 		soongBuildMetrics := loadSoongBuildMetrics(ctx, config)
-		logSoongBuildMetrics(ctx, soongBuildMetrics)
+		if soongBuildMetrics != nil {
+			logSoongBuildMetrics(ctx, soongBuildMetrics)
+			if ctx.Metrics != nil {
+				ctx.Metrics.SetSoongBuildMetrics(soongBuildMetrics)
+			}
+		}
 	}
 
 	distGzipFile(ctx, config, config.SoongNinjaFile(), "soong")
@@ -504,9 +510,6 @@ func runSoong(ctx Context, config Config) {
 		distGzipFile(ctx, config, config.SoongMakeVarsMk(), "soong")
 	}
 
-	if shouldCollectBuildSoongMetrics(config) && ctx.Metrics != nil {
-		ctx.Metrics.SetSoongBuildMetrics(soongBuildMetrics)
-	}
 	if config.JsonModuleGraph() {
 		distGzipFile(ctx, config, config.ModuleGraphFile(), "soong")
 	}
@@ -538,8 +541,12 @@ func shouldCollectBuildSoongMetrics(config Config) bool {
 
 func loadSoongBuildMetrics(ctx Context, config Config) *soong_metrics_proto.SoongBuildMetrics {
 	soongBuildMetricsFile := filepath.Join(config.LogsDir(), "soong_build_metrics.pb")
-	buf, err := ioutil.ReadFile(soongBuildMetricsFile)
-	if err != nil {
+	buf, err := os.ReadFile(soongBuildMetricsFile)
+	if errors.Is(err, fs.ErrNotExist) {
+		// Soong may not have run during this invocation
+          ctx.Verbosef("Failed to read metrics file, %s: %s", soongBuildMetricsFile, err)
+		return nil
+	} else if err != nil {
 		ctx.Fatalf("Failed to load %s: %s", soongBuildMetricsFile, err)
 	}
 	soongBuildMetrics := &soong_metrics_proto.SoongBuildMetrics{}