tracing/gotrace: Fix tests for Go1.10 where CGo is now supported

Go1.10 now modifies CGo sources as text, not AST, and this way comments
are not removed and gotrace can see its '//trace:event ' comments in a
CGo *.go files: https://github.com/golang/go/commit/85c3ebf4.

This way with Go1.10 tests were failing because `//trace:event
traceHello()` in a/pkg1/pkg1c.go was now noticed by gotrace and more
then expected trace events produces.

I have not noticed this in 65c399f0 (tracing/runtime: Add support for
Go1.10 (preliminary)) probably because at that time above Go commit was
not in my local Go1.10 tree.

For the reference: tracing/runtime support regenerated for Go1.10.2
stays exactly the same as in 65c399f0 and so does not need updating.

tracing/cmd/gotrace/gotrace.go

-// Copyright (C) 2017  Nexedi SA and Contributors.
+// Copyright (C) 2018  Nexedi SA and Contributors.
 //                     Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -281,10 +281,9 @@ func packageTrace(prog *loader.Program, pkgi *loader.PackageInfo) (*Package, err
 
 	// go through files of the original package and process //trace: directives
 	//
-	// FIXME we currently don't process cgo files as go/loader passes to us
+	// NOTE before go1.10 we don't process cgo files as there go/loader passes to us
 	// already preprocessed results with comments stripped, not original source.
-	// Maybe in some time it will be possible to have AST of original source:
-	// https://golang.org/issues/16623
+	// This problem was fixed for go1.10 in https://github.com/golang/go/commit/85c3ebf4.
 	for _, file := range pkgi.Files {                        // ast.File
 		for _, commgroup := range file.Comments {        // ast.CommentGroup
 			for _, comment := range commgroup.List { // ast.Comment

tracing/cmd/gotrace/gotrace_test.go

@@ -134,6 +134,16 @@ func diffR(patha, pathb string) (diff string, err error) {
 	return string(out), err
 }
 
+// haveReleaseTag returns whether current compiler has specified tag in its default build environment.
+func haveReleaseTag(tag string) bool {
+	for _, rtag := range build.Default.ReleaseTags {
+		if tag == rtag {
+			return true
+		}
+	}
+	return false
+}
+
 func TestGoTrace(t *testing.T) {
 	tmp, err := ioutil.TempDir("", "t-gotrace")
 	if err != nil {
@@ -159,6 +169,10 @@ func TestGoTrace(t *testing.T) {
 
 	// XXX autodetect (go list ?)
 	testv := []string{"a/pkg1", "b/pkg2", "c/pkg3", "d/pkg4"}
+	// cgo parsing works starting with Go 1.10
+	if haveReleaseTag("go1.10") {
+		testv = append(testv, "a/pkg1_cgo")
+	}
 
 	for _, tpkg := range testv {
 		// verify `gotrace gen`

tracing/cmd/gotrace/testdata/src/a/pkg1/pkg1c.go → tracing/cmd/gotrace/testdata/src/a/pkg1_cgo/pkg1c.go

@@ -9,13 +9,10 @@ void hello() {
 */
 import "C"
 
-// FIXME vvv does not currently work because go/loader gives us already
-// preprocessed result without original comments.
-//
 // trace event defined in a cgo file
-//trace:event traceHello()
+//trace:event traceCHello()
 
 func Hello() {
-	//traceHello()
+	traceCHello()
 	C.hello()
 }

tracing/cmd/gotrace/testdata/src/a/pkg1_cgo/tracelist.txt

+a/pkg1_cgo:traceCHello

tracing/cmd/gotrace/testdata/src/a/pkg1_cgo/ztrace.go.ok

+// Code generated by lab.nexedi.com/kirr/go123/tracing/cmd/gotrace; DO NOT EDIT.
+
+package pkg1
+// code generated for tracepoints
+
+import (
+	"lab.nexedi.com/kirr/go123/tracing"
+	"unsafe"
+)
+
+// traceevent: traceCHello()
+
+type _t_traceCHello struct {
+	tracing.Probe
+	probefunc     func()
+}
+
+var _traceCHello *_t_traceCHello
+
+func traceCHello() {
+	if _traceCHello != nil {
+		_traceCHello_run()
+	}
+}
+
+func _traceCHello_run() {
+	for p := _traceCHello; p != nil; p = (*_t_traceCHello)(unsafe.Pointer(p.Next())) {
+		p.probefunc()
+	}
+}
+
+func traceCHello_Attach(pg *tracing.ProbeGroup, probe func()) *tracing.Probe {
+	p := _t_traceCHello{probefunc: probe}
+	tracing.AttachProbe(pg, (**tracing.Probe)(unsafe.Pointer(&_traceCHello)), &p.Probe)
+	return &p.Probe
+}
+
+// trace export signature
+func _trace_exporthash_6c1e623c8877bd3e4d9efc72e73ac2bdbf56462b() {}