Add a dependency fixer for proto deps

protoc dependency files, at least for C++ outputs, uses the form of:

  a/b.c \
  a/b.h: <dep1> <dep2>...

Ninja will fail the command when it parses a dep file and there's more
than one output file (even though it doesn't care what the output file
name is). So this tool will parse the original file, and output a
version with only a single output file.

Bug: 67329638
Test: NINJA_ARGS="-t deps ...pb.c" m
Test: NINJA_ARGS="-t deps ...srcjar" m
Test: NINJA_ARGS="-t deps ...srcszip" m
Test: Run dep_fixer across all of taimen's dep files, no failures.
Test: Run dep_fixer against the processed files, no changes.
Test: Run androidmk across all of our Android.mk files, inspect the diffs
Change-Id: I4263b7d5faea37285afa6b24dedf5964aa7d19dc

4 files changed, 574 insertions, 0 deletions

diff --git a/cmd/dep_fixer/Android.bp b/cmd/dep_fixer/Android.bp
new file mode 100644
index 00000000..d2d1113d
--- /dev/null
+++ b/cmd/dep_fixer/Android.bp
@@ -0,0 +1,23 @@
+// Copyright 2018 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.
+
+blueprint_go_binary {
+    name: "dep_fixer",
+    deps: ["androidmk-parser"],
+    srcs: [
+        "main.go",
+        "deps.go",
+    ],
+    testSrcs: ["deps_test.go"],
+}
diff --git a/cmd/dep_fixer/deps.go b/cmd/dep_fixer/deps.go
new file mode 100644
index 00000000..64c97f52
--- /dev/null
+++ b/cmd/dep_fixer/deps.go
@@ -0,0 +1,95 @@
+// Copyright 2018 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.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"strings"
+
+	"android/soong/androidmk/parser"
+)
+
+type Deps struct {
+	Output string
+	Inputs []string
+}
+
+func Parse(filename string, r io.Reader) (*Deps, error) {
+	p := parser.NewParser(filename, r)
+	nodes, errs := p.Parse()
+
+	if len(errs) == 1 {
+		return nil, errs[0]
+	} else if len(errs) > 1 {
+		return nil, fmt.Errorf("many errors: %v", errs)
+	}
+
+	pos := func(node parser.Node) string {
+		return p.Unpack(node.Pos()).String() + ": "
+	}
+
+	ret := &Deps{}
+
+	for _, node := range nodes {
+		switch x := node.(type) {
+		case *parser.Comment:
+			// Do nothing
+		case *parser.Rule:
+			if x.Recipe != "" {
+				return nil, fmt.Errorf("%sunexpected recipe in rule: %v", pos(node), x)
+			}
+
+			if !x.Target.Const() {
+				return nil, fmt.Errorf("%sunsupported variable expansion: %v", pos(node), x.Target.Dump())
+			}
+			outputs := x.Target.Words()
+			if len(outputs) == 0 {
+				return nil, fmt.Errorf("%smissing output: %v", pos(node), x)
+			}
+			ret.Output = outputs[0].Value(nil)
+
+			if !x.Prerequisites.Const() {
+				return nil, fmt.Errorf("%sunsupported variable expansion: %v", pos(node), x.Prerequisites.Dump())
+			}
+			for _, input := range x.Prerequisites.Words() {
+				ret.Inputs = append(ret.Inputs, input.Value(nil))
+			}
+		default:
+			return nil, fmt.Errorf("%sunexpected line: %#v", pos(node), node)
+		}
+	}
+
+	return ret, nil
+}
+
+func (d *Deps) Print() []byte {
+	// We don't really have to escape every \, but it's simpler,
+	// and ninja will handle it.
+	replacer := strings.NewReplacer(" ", "\\ ",
+		":", "\\:",
+		"#", "\\#",
+		"$", "$$",
+		"\\", "\\\\")
+
+	b := &bytes.Buffer{}
+	fmt.Fprintf(b, "%s:", replacer.Replace(d.Output))
+	for _, input := range d.Inputs {
+		fmt.Fprintf(b, " %s", replacer.Replace(input))
+	}
+	fmt.Fprintln(b)
+	return b.Bytes()
+}
diff --git a/cmd/dep_fixer/deps_test.go b/cmd/dep_fixer/deps_test.go
new file mode 100644
index 00000000..0a779b76
--- /dev/null
+++ b/cmd/dep_fixer/deps_test.go
@@ -0,0 +1,389 @@
+// Copyright 2018 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.
+
+package main
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestParse(t *testing.T) {
+	testCases := []struct {
+		name   string
+		input  string
+		output Deps
+		err    error
+	}{
+		// These come from the ninja test suite
+		{
+			name:  "Basic",
+			input: "build/ninja.o: ninja.cc ninja.h eval_env.h manifest_parser.h",
+			output: Deps{
+				Output: "build/ninja.o",
+				Inputs: []string{
+					"ninja.cc",
+					"ninja.h",
+					"eval_env.h",
+					"manifest_parser.h",
+				},
+			},
+		},
+		{
+			name: "EarlyNewlineAndWhitespace",
+			input: ` \
+  out: in`,
+			output: Deps{
+				Output: "out",
+				Inputs: []string{"in"},
+			},
+		},
+		{
+			name: "Continuation",
+			input: `foo.o: \
+  bar.h baz.h
+`,
+			output: Deps{
+				Output: "foo.o",
+				Inputs: []string{"bar.h", "baz.h"},
+			},
+		},
+		{
+			name:  "CarriageReturnContinuation",
+			input: "foo.o: \\\r\n  bar.h baz.h\r\n",
+			output: Deps{
+				Output: "foo.o",
+				Inputs: []string{"bar.h", "baz.h"},
+			},
+		},
+		{
+			name: "BackSlashes",
+			input: `Project\Dir\Build\Release8\Foo\Foo.res : \
+  Dir\Library\Foo.rc \
+  Dir\Library\Version\Bar.h \
+  Dir\Library\Foo.ico \
+  Project\Thing\Bar.tlb \
+`,
+			output: Deps{
+				Output: `Project\Dir\Build\Release8\Foo\Foo.res`,
+				Inputs: []string{
+					`Dir\Library\Foo.rc`,
+					`Dir\Library\Version\Bar.h`,
+					`Dir\Library\Foo.ico`,
+					`Project\Thing\Bar.tlb`,
+				},
+			},
+		},
+		{
+			name:  "Spaces",
+			input: `a\ bc\ def:   a\ b c d`,
+			output: Deps{
+				Output: `a bc def`,
+				Inputs: []string{"a b", "c", "d"},
+			},
+		},
+		{
+			name:  "Escapes",
+			input: `\!\@\#$$\%\^\&\\:`,
+			output: Deps{
+				Output: `\!\@#$\%\^\&\`,
+			},
+		},
+		{
+			name: "SpecialChars",
+			// Ninja includes a number of '=', but our parser can't handle that,
+			// since it sees the equals and switches over to assuming it's an
+			// assignment.
+			//
+			// We don't have any files in our tree that contain an '=' character,
+			// and Kati can't handle parsing this either, so for now I'm just
+			// going to remove all the '=' characters below.
+			//
+			// It looks like make will only do this for the first
+			// dependency, but not later dependencies.
+			input: `C\:/Program\ Files\ (x86)/Microsoft\ crtdefs.h: \
+ en@quot.header~ t+t-x!1 \
+ openldap/slapd.d/cnconfig/cnschema/cn{0}core.ldif \
+ Fu` + "\303\244ball",
+			output: Deps{
+				Output: "C:/Program Files (x86)/Microsoft crtdefs.h",
+				Inputs: []string{
+					"en@quot.header~",
+					"t+t-x!1",
+					"openldap/slapd.d/cnconfig/cnschema/cn{0}core.ldif",
+					"Fu\303\244ball",
+				},
+			},
+		},
+		// Ninja's UnifyMultipleOutputs and RejectMultipleDifferentOutputs tests have been omitted,
+		// since we don't want the same behavior.
+
+		// Our own tests
+		{
+			name: "Multiple outputs",
+			input: `a b: c
+a: d
+b: e`,
+			output: Deps{
+				Output: "b",
+				Inputs: []string{
+					"c",
+					"d",
+					"e",
+				},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			out, err := Parse("test.d", bytes.NewBufferString(tc.input))
+			if err != tc.err {
+				t.Fatalf("Unexpected error: %v (expected %v)", err, tc.err)
+			}
+
+			if out.Output != tc.output.Output {
+				t.Errorf("output file doesn't match:\n"+
+					" str: %#v\n"+
+					"want: %#v\n"+
+					" got: %#v", tc.input, tc.output.Output, out.Output)
+			}
+
+			matches := true
+			if len(out.Inputs) != len(tc.output.Inputs) {
+				matches = false
+			} else {
+				for i := range out.Inputs {
+					if out.Inputs[i] != tc.output.Inputs[i] {
+						matches = false
+					}
+				}
+			}
+			if !matches {
+				t.Errorf("input files don't match:\n"+
+					" str: %#v\n"+
+					"want: %#v\n"+
+					" got: %#v", tc.input, tc.output.Inputs, out.Inputs)
+			}
+		})
+	}
+}
+
+func BenchmarkParsing(b *testing.B) {
+	// Write it out to a file to most closely match ninja's perftest
+	tmpfile, err := ioutil.TempFile("", "depfile")
+	if err != nil {
+		b.Fatal("Failed to create temp file:", err)
+	}
+	defer os.Remove(tmpfile.Name())
+	_, err = io.WriteString(tmpfile, `out/soong/.intermediates/external/ninja/ninja/linux_glibc_x86_64/obj/external/ninja/src/ninja.o: \
+  external/ninja/src/ninja.cc external/libcxx/include/errno.h \
+  external/libcxx/include/__config \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/features.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/predefs.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/sys/cdefs.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/wordsize.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/gnu/stubs.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/gnu/stubs-64.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/errno.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/errno.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/linux/errno.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/asm/errno.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/asm-generic/errno.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/asm-generic/errno-base.h \
+  external/libcxx/include/limits.h \
+  prebuilts/clang/host/linux-x86/clang-4639204/lib64/clang/6.0.1/include/limits.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/limits.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/posix1_lim.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/local_lim.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/linux/limits.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/posix2_lim.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/xopen_lim.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/stdio_lim.h \
+  external/libcxx/include/stdio.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/stdio.h \
+  external/libcxx/include/stddef.h \
+  prebuilts/clang/host/linux-x86/clang-4639204/lib64/clang/6.0.1/include/stddef.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/types.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/typesizes.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/libio.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/_G_config.h \
+  external/libcxx/include/wchar.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/wchar.h \
+  prebuilts/clang/host/linux-x86/clang-4639204/lib64/clang/6.0.1/include/stdarg.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/sys_errlist.h \
+  external/libcxx/include/stdlib.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/stdlib.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/waitflags.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/waitstatus.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/endian.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/endian.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/byteswap.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/xlocale.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/sys/types.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/time.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/sys/select.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/select.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/sigset.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/time.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/select2.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/sys/sysmacros.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/pthreadtypes.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/alloca.h \
+  external/libcxx/include/string.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/string.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/getopt.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/unistd.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/posix_opt.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/environments.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/confname.h \
+  external/ninja/src/browse.h external/ninja/src/build.h \
+  external/libcxx/include/cstdio external/libcxx/include/map \
+  external/libcxx/include/__tree external/libcxx/include/iterator \
+  external/libcxx/include/iosfwd \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/wchar.h \
+  external/libcxx/include/__functional_base \
+  external/libcxx/include/type_traits external/libcxx/include/cstddef \
+  prebuilts/clang/host/linux-x86/clang-4639204/lib64/clang/6.0.1/include/__stddef_max_align_t.h \
+  external/libcxx/include/__nullptr external/libcxx/include/typeinfo \
+  external/libcxx/include/exception external/libcxx/include/cstdlib \
+  external/libcxx/include/cstdint external/libcxx/include/stdint.h \
+  prebuilts/clang/host/linux-x86/clang-4639204/lib64/clang/6.0.1/include/stdint.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/stdint.h \
+  external/libcxx/include/new external/libcxx/include/utility \
+  external/libcxx/include/__tuple \
+  external/libcxx/include/initializer_list \
+  external/libcxx/include/cstring external/libcxx/include/__debug \
+  external/libcxx/include/memory external/libcxx/include/limits \
+  external/libcxx/include/__undef_macros external/libcxx/include/tuple \
+  external/libcxx/include/stdexcept external/libcxx/include/cassert \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/assert.h \
+  external/libcxx/include/atomic external/libcxx/include/algorithm \
+  external/libcxx/include/functional external/libcxx/include/queue \
+  external/libcxx/include/deque external/libcxx/include/__split_buffer \
+  external/libcxx/include/vector external/libcxx/include/__bit_reference \
+  external/libcxx/include/climits external/libcxx/include/set \
+  external/libcxx/include/string external/libcxx/include/string_view \
+  external/libcxx/include/__string external/libcxx/include/cwchar \
+  external/libcxx/include/cwctype external/libcxx/include/cctype \
+  external/libcxx/include/ctype.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/ctype.h \
+  external/libcxx/include/wctype.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/wctype.h \
+  external/ninja/src/graph.h external/ninja/src/eval_env.h \
+  external/ninja/src/string_piece.h external/ninja/src/timestamp.h \
+  external/ninja/src/util.h external/ninja/src/exit_status.h \
+  external/ninja/src/line_printer.h external/ninja/src/metrics.h \
+  external/ninja/src/build_log.h external/ninja/src/hash_map.h \
+  external/libcxx/include/unordered_map \
+  external/libcxx/include/__hash_table external/libcxx/include/cmath \
+  external/libcxx/include/math.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/math.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/huge_val.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/huge_valf.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/huge_vall.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/inf.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/nan.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/mathdef.h \
+  prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/include/x86_64-linux-gnu/bits/mathcalls.h \
+  external/ninja/src/deps_log.h external/ninja/src/clean.h \
+  external/ninja/src/debug_flags.h external/ninja/src/disk_interface.h \
+  external/ninja/src/graphviz.h external/ninja/src/manifest_parser.h \
+  external/ninja/src/lexer.h external/ninja/src/state.h \
+  external/ninja/src/version.h`)
+	tmpfile.Close()
+	if err != nil {
+		b.Fatal("Failed to write dep file:", err)
+	}
+	b.ResetTimer()
+
+	for n := 0; n < b.N; n++ {
+		depfile, err := ioutil.ReadFile(tmpfile.Name())
+		if err != nil {
+			b.Fatal("Failed to read dep file:", err)
+		}
+
+		_, err = Parse(tmpfile.Name(), bytes.NewBuffer(depfile))
+		if err != nil {
+			b.Fatal("Failed to parse:", err)
+		}
+	}
+}
+
+func TestDepPrint(t *testing.T) {
+	testCases := []struct {
+		name   string
+		input  Deps
+		output string
+	}{
+		{
+			name: "Empty",
+			input: Deps{
+				Output: "a",
+			},
+			output: "a:",
+		},
+		{
+			name: "Basic",
+			input: Deps{
+				Output: "a",
+				Inputs: []string{"b", "c"},
+			},
+			output: "a: b c",
+		},
+		{
+			name: "Escapes",
+			input: Deps{
+				Output: `\!\@#$\%\^\&\`,
+			},
+			output: `\\!\\@\#$$\\%\\^\\&\\:`,
+		},
+		{
+			name: "Spaces",
+			input: Deps{
+				Output: "a b",
+				Inputs: []string{"c d", "e f "},
+			},
+			output: `a\ b: c\ d e\ f\ `,
+		},
+		{
+			name: "SpecialChars",
+			input: Deps{
+				Output: "C:/Program Files (x86)/Microsoft crtdefs.h",
+				Inputs: []string{
+					"en@quot.header~",
+					"t+t-x!1",
+					"openldap/slapd.d/cnconfig/cnschema/cn{0}core.ldif",
+					"Fu\303\244ball",
+				},
+			},
+			output: `C\:/Program\ Files\ (x86)/Microsoft\ crtdefs.h: en@quot.header~ t+t-x!1 openldap/slapd.d/cnconfig/cnschema/cn{0}core.ldif Fu` + "\303\244ball",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			out := tc.input.Print()
+			outStr := string(out)
+			want := tc.output + "\n"
+
+			if outStr != want {
+				t.Errorf("output doesn't match:\nwant:%q\n got:%q", want, outStr)
+			}
+		})
+	}
+}
diff --git a/cmd/dep_fixer/main.go b/cmd/dep_fixer/main.go
new file mode 100644
index 00000000..bac3772b
--- /dev/null
+++ b/cmd/dep_fixer/main.go
@@ -0,0 +1,67 @@
+// Copyright 2018 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.
+
+// This tool reads "make"-like dependency files, and outputs a canonical version
+// that can be used by ninja. Ninja doesn't support multiple output files (even
+// though it doesn't care what the output file is, or whether it matches what is
+// expected).
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+)
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "Usage: %s <depfile.d>")
+		flag.PrintDefaults()
+	}
+	output := flag.String("o", "", "Optional output file (defaults to rewriting source if necessary)")
+	flag.Parse()
+
+	if flag.NArg() != 1 {
+		log.Fatal("Expected a single file as an argument")
+	}
+
+	old, err := ioutil.ReadFile(flag.Arg(0))
+	if err != nil {
+		log.Fatalf("Error opening %q: %v", flag.Arg(0), err)
+	}
+
+	deps, err := Parse(flag.Arg(0), bytes.NewBuffer(append([]byte(nil), old...)))
+	if err != nil {
+		log.Fatalf("Failed to parse: %v", err)
+	}
+
+	new := deps.Print()
+
+	if *output == "" || *output == flag.Arg(0) {
+		if !bytes.Equal(old, new) {
+			err := ioutil.WriteFile(flag.Arg(0), new, 0666)
+			if err != nil {
+				log.Fatalf("Failed to write: %v", err)
+			}
+		}
+	} else {
+		err := ioutil.WriteFile(*output, new, 0666)
+		if err != nil {
+			log.Fatalf("Failed to write to %q: %v", *output, err)
+		}
+	}
+}