Convert soong_javac_filter to a wrapper

Piping the output of javac through a filter makes it hard to capture
the exit status.  Convert it to a wrapper that executes javac and
propagates the exit status.

Bug: 36666657
Test: javac_wrapper_test
Change-Id: I9b56cc3794023aabc9328138a68830e26e980f97
diff --git a/cmd/javac_wrapper/javac_wrapper.go b/cmd/javac_wrapper/javac_wrapper.go
new file mode 100644
index 0000000..a323473
--- /dev/null
+++ b/cmd/javac_wrapper/javac_wrapper.go
@@ -0,0 +1,173 @@
+// Copyright 2017 Google Inc. 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.
+
+// soong_javac_wrapper expects a javac command line and argments, executes
+// it, and produces an ANSI colorized version of the output on stdout.
+//
+// It also hides the unhelpful and unhideable "warning there is a warning"
+// messages.
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"regexp"
+	"syscall"
+)
+
+// Regular expressions are based on
+// https://chromium.googlesource.com/chromium/src/+/master/build/android/gyp/javac.py
+// Colors are based on clang's output
+var (
+	filelinePrefix = `^([-.\w/\\]+.java:[0-9]+: )`
+	warningRe      = regexp.MustCompile(filelinePrefix + `?(warning:) .*$`)
+	errorRe        = regexp.MustCompile(filelinePrefix + `(.*?:) .*$`)
+	markerRe       = regexp.MustCompile(`()\s*(\^)\s*$`)
+
+	escape  = "\x1b"
+	reset   = escape + "[0m"
+	bold    = escape + "[1m"
+	red     = escape + "[31m"
+	green   = escape + "[32m"
+	magenta = escape + "[35m"
+)
+
+func main() {
+	exitCode, err := Main(os.Args[0], os.Args[1:])
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err.Error())
+	}
+	os.Exit(exitCode)
+}
+
+func Main(name string, args []string) (int, error) {
+	if len(args) < 1 {
+		return 1, fmt.Errorf("usage: %s javac ...", name)
+	}
+
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return 1, fmt.Errorf("creating output pipe: %s", err)
+	}
+
+	cmd := exec.Command(args[0], args[1:]...)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = pw
+	cmd.Stderr = pw
+	err = cmd.Start()
+	if err != nil {
+		return 1, fmt.Errorf("starting subprocess: %s", err)
+	}
+
+	pw.Close()
+
+	// Process subprocess stdout asynchronously
+	errCh := make(chan error)
+	go func() {
+		errCh <- process(pr, os.Stdout)
+	}()
+
+	// Wait for subprocess to finish
+	cmdErr := cmd.Wait()
+
+	// Wait for asynchronous stdout processing to finish
+	err = <-errCh
+
+	// Check for subprocess exit code
+	if cmdErr != nil {
+		if exitErr, ok := cmdErr.(*exec.ExitError); ok {
+			if status, ok := exitErr.Sys().(syscall.WaitStatus); ok {
+				if status.Exited() {
+					return status.ExitStatus(), nil
+				} else if status.Signaled() {
+					exitCode := 128 + int(status.Signal())
+					return exitCode, nil
+				} else {
+					return 1, exitErr
+				}
+			} else {
+				return 1, nil
+			}
+		}
+	}
+
+	if err != nil {
+		return 1, err
+	}
+
+	return 0, nil
+}
+
+func process(r io.Reader, w io.Writer) error {
+	scanner := bufio.NewScanner(r)
+	// Some javac wrappers output the entire list of java files being
+	// compiled on a single line, which can be very large, set the maximum
+	// buffer size to 2MB.
+	scanner.Buffer(nil, 2*1024*1024)
+	for scanner.Scan() {
+		processLine(w, scanner.Text())
+	}
+	err := scanner.Err()
+	if err != nil {
+		return fmt.Errorf("scanning input: %s", err)
+	}
+	return nil
+}
+
+func processLine(w io.Writer, line string) {
+	for _, f := range filters {
+		if f.MatchString(line) {
+			return
+		}
+	}
+	for _, p := range colorPatterns {
+		var matched bool
+		if line, matched = applyColor(line, p.color, p.re); matched {
+			break
+		}
+	}
+	fmt.Fprintln(w, line)
+}
+
+// If line matches re, make it bold and apply color to the first submatch
+// Returns line, modified if it matched, and true if it matched.
+func applyColor(line, color string, re *regexp.Regexp) (string, bool) {
+	if m := re.FindStringSubmatchIndex(line); m != nil {
+		tagStart, tagEnd := m[4], m[5]
+		line = bold + line[:tagStart] +
+			color + line[tagStart:tagEnd] + reset + bold +
+			line[tagEnd:] + reset
+		return line, true
+	}
+	return line, false
+}
+
+var colorPatterns = []struct {
+	re    *regexp.Regexp
+	color string
+}{
+	{warningRe, magenta},
+	{errorRe, red},
+	{markerRe, green},
+}
+
+var filters = []*regexp.Regexp{
+	regexp.MustCompile(`Note: (Some input files|.*\.java) uses? or overrides? a deprecated API.`),
+	regexp.MustCompile(`Note: Recompile with -Xlint:deprecation for details.`),
+	regexp.MustCompile(`Note: (Some input files|.*\.java) uses? unchecked or unsafe operations.`),
+	regexp.MustCompile(`Note: Recompile with -Xlint:unchecked for details.`),
+}