internal/profile: actually return errors in postDecode

As spotted by staticcheck, the body did keep track of errors by sharing
a single err variable, but its last value was never used as the function
simply finished by returning nil.

To prevent postDecode from erroring on empty profiles,
which breaks TestEmptyProfile, add a check at the top of the function.

Update the runtime/pprof test accordingly,
since the default units didn't make sense for an empty profile anyway.

Change-Id: I188cd8337434adf9169651ab5c914731b8b20f39
Reviewed-on: https://go-review.googlesource.com/c/go/+/483137
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 2 insertions, 6 deletions

diff --git a/src/runtime/pprof/proto_test.go b/src/runtime/pprof/proto_test.go
index f788b167da..e1a7f2306d 100644
--- a/src/runtime/pprof/proto_test.go
+++ b/src/runtime/pprof/proto_test.go
@@ -64,13 +64,9 @@ func TestConvertCPUProfileEmpty(t *testing.T) {
 	}
 
 	// Expected PeriodType and SampleType.
-	periodType := &profile.ValueType{Type: "cpu", Unit: "nanoseconds"}
-	sampleType := []*profile.ValueType{
-		{Type: "samples", Unit: "count"},
-		{Type: "cpu", Unit: "nanoseconds"},
-	}
+	sampleType := []*profile.ValueType{{}, {}}
 
-	checkProfile(t, p, 2000*1000, periodType, sampleType, nil, "")
+	checkProfile(t, p, 2000*1000, nil, sampleType, nil, "")
 }
 
 func f1() { f1() }