build: Make fewer copies of NewBuildContext.

dmitshur · dmitshur · commit f681903bc8cc · 2018-04-20T17:05:10.000-04:00
Call NewBuildContext at the top of Import, ImportDir, and inside
NewSession.

Previously, it was called more often than necessary (instead of being
preserved for entire build session).

Pass build context by value to importWithSrcDir so it can be safely
modified there, without the changes persisisting from one package
to the next.

The build context will need to be available in more places in an
upcoming commit. Storing it in Session helps with that.
diff --git a/build/build.go b/build/build.go
@@ -33,6 +33,8 @@ func (e *ImportCError) Error() string {
 	return e.pkgPath + `: importing "C" is not supported by GopherJS`
 }
 
+// NewBuildContext creates a build context for building Go packages
+// with GopherJS compiler.
 func NewBuildContext(installSuffix string, buildTags []string) *build.Context {
 	return &build.Context{
 		GOROOT:        build.Default.GOROOT,
@@ -72,11 +74,12 @@ func Import(path string, mode build.ImportMode, installSuffix string, buildTags
 		// Import will not be able to resolve relative import paths.
 		wd = ""
 	}
-	return importWithSrcDir(path, wd, mode, installSuffix, buildTags)
+	bctx := NewBuildContext(installSuffix, buildTags)
+	return importWithSrcDir(*bctx, path, wd, mode, installSuffix)
 }
 
-func importWithSrcDir(path string, srcDir string, mode build.ImportMode, installSuffix string, buildTags []string) (*PackageData, error) {
-	bctx := NewBuildContext(installSuffix, buildTags)
+func importWithSrcDir(bctx build.Context, path string, srcDir string, mode build.ImportMode, installSuffix string) (*PackageData, error) {
+	// bctx is passed by value, so it can be modified here.
 	switch path {
 	case "syscall":
 		// syscall needs to use a typical GOARCH like amd64 to pick up definitions for _Socklen, BpfInsn, IFNAMSIZ, Timeval, BpfStat, SYS_FCNTL, Flock_t, etc.
@@ -410,6 +413,7 @@ type PackageData struct {
 
 type Session struct {
 	options  *Options
+	bctx     *build.Context
 	Archives map[string]*compiler.Archive
 	Types    map[string]*types.Package
 	Watcher  *fsnotify.Watcher
@@ -428,6 +432,7 @@ func NewSession(options *Options) *Session {
 		options:  options,
 		Archives: make(map[string]*compiler.Archive),
 	}
+	s.bctx = NewBuildContext(s.InstallSuffix(), s.options.BuildTags)
 	s.Types = make(map[string]*types.Package)
 	if options.Watch {
 		if out, err := exec.Command("ulimit", "-n").Output(); err == nil {
@@ -456,7 +461,7 @@ func (s *Session) BuildDir(packagePath string, importPath string, pkgObj string)
 	if s.Watcher != nil {
 		s.Watcher.Add(packagePath)
 	}
-	buildPkg, err := NewBuildContext(s.InstallSuffix(), s.options.BuildTags).ImportDir(packagePath, 0)
+	buildPkg, err := s.bctx.ImportDir(packagePath, 0)
 	if err != nil {
 		return err
 	}
@@ -514,7 +519,7 @@ func (s *Session) BuildImportPath(path string) (*compiler.Archive, error) {
 }
 
 func (s *Session) buildImportPathWithSrcDir(path string, srcDir string) (*PackageData, *compiler.Archive, error) {
-	pkg, err := importWithSrcDir(path, srcDir, 0, s.InstallSuffix(), s.options.BuildTags)
+	pkg, err := importWithSrcDir(*s.bctx, path, srcDir, 0, s.InstallSuffix())
 	if s.Watcher != nil && pkg != nil { // add watch even on error
 		s.Watcher.Add(pkg.Dir)
 	}
