1 files changed, 168 insertions, 0 deletions
diff --git a/go/tools/builders/filter.go b/go/tools/builders/filter.go
new file mode 100644
index 00000000..fbb0f2ac
--- /dev/null
+++ b/go/tools/builders/filter.go
@@ -0,0 +1,168 @@
+// Copyright 2017 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"fmt"
+	"go/ast"
+	"go/build"
+	"go/token"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+type fileInfo struct {
+	filename string
+	ext      ext
+	header   []byte
+	fset     *token.FileSet
+	parsed   *ast.File
+	parseErr error
+	matched  bool
+	isCgo    bool
+	pkg      string
+	imports  []fileImport
+	embeds   []fileEmbed
+}
+
+type ext int
+
+const (
+	goExt ext = iota
+	cExt
+	cxxExt
+	objcExt
+	objcxxExt
+	sExt
+	hExt
+)
+
+type fileImport struct {
+	path string
+	pos  token.Pos
+	doc  *ast.CommentGroup
+}
+
+type fileEmbed struct {
+	pattern string
+	pos     token.Position
+}
+
+type archiveSrcs struct {
+	goSrcs, cSrcs, cxxSrcs, objcSrcs, objcxxSrcs, sSrcs, hSrcs []fileInfo
+}
+
+// filterAndSplitFiles filters files using build constraints and collates
+// them by extension.
+func filterAndSplitFiles(fileNames []string) (archiveSrcs, error) {
+	var res archiveSrcs
+	for _, s := range fileNames {
+		src, err := readFileInfo(build.Default, s)
+		if err != nil {
+			return archiveSrcs{}, err
+		}
+		if !src.matched {
+			continue
+		}
+		var srcs *[]fileInfo
+		switch src.ext {
+		case goExt:
+			srcs = &res.goSrcs
+		case cExt:
+			srcs = &res.cSrcs
+		case cxxExt:
+			srcs = &res.cxxSrcs
+		case objcExt:
+			srcs = &res.objcSrcs
+		case objcxxExt:
+			srcs = &res.objcxxSrcs
+		case sExt:
+			srcs = &res.sSrcs
+		case hExt:
+			srcs = &res.hSrcs
+		}
+		*srcs = append(*srcs, src)
+	}
+	return res, nil
+}
+
+// readFileInfo applies build constraints to an input file and returns whether
+// it should be compiled.
+func readFileInfo(bctx build.Context, input string) (fileInfo, error) {
+	fi := fileInfo{filename: input}
+	if ext := filepath.Ext(input); ext == ".C" {
+		fi.ext = cxxExt
+	} else {
+		switch strings.ToLower(ext) {
+		case ".go":
+			fi.ext = goExt
+		case ".c":
+			fi.ext = cExt
+		case ".cc", ".cxx", ".cpp":
+			fi.ext = cxxExt
+		case ".m":
+			fi.ext = objcExt
+		case ".mm":
+			fi.ext = objcxxExt
+		case ".s":
+			fi.ext = sExt
+		case ".h", ".hh", ".hpp", ".hxx":
+			fi.ext = hExt
+		default:
+			return fileInfo{}, fmt.Errorf("unrecognized file extension: %s", ext)
+		}
+	}
+
+	dir, base := filepath.Split(input)
+	// Check build constraints on non-cgo files.
+	// Skip cgo files, since they get rejected (due to leading '_') and won't
+	// have any build constraints anyway.
+	if strings.HasPrefix(base, "_cgo") {
+		fi.matched = true
+	} else {
+		match, err := bctx.MatchFile(dir, base)
+		if err != nil {
+			return fi, err
+		}
+		fi.matched = match
+	}
+	// If it's not a go file, there's nothing more to read.
+	if fi.ext != goExt {
+		return fi, nil
+	}
+
+	// Scan the file for imports and embeds.
+	f, err := os.Open(input)
+	if err != nil {
+		return fileInfo{}, err
+	}
+	defer f.Close()
+	fi.fset = token.NewFileSet()
+	if err := readGoInfo(f, &fi); err != nil {
+		return fileInfo{}, err
+	}
+
+	// Exclude cgo files if cgo is not enabled.
+	for _, imp := range fi.imports {
+		if imp.path == "C" {
+			fi.isCgo = true
+			break
+		}
+	}
+	fi.matched = fi.matched && (bctx.CgoEnabled || !fi.isCgo)
+
+	return fi, nil
+}