make output binaries deterministic

We were leaking temporary file paths, which is no longer the case.

README.md

@@ -18,7 +18,7 @@ information about the original source code as possible.
 The tool is designed to be:
 
 * Coupled with `cmd/go`, to support both `GOPATH` and modules with ease
-* Deterministic, though the output is not yet reproducible
+* Deterministic and reproducible, given the same initial source code
 * Reversible given the original source, to un-garble panic stack traces
 
 ### Mechanism

main.go

@@ -197,10 +197,24 @@ func transformCompile(args []string) ([]string, error) {
 		return nil, fmt.Errorf("typecheck error: %v", err)
 	}
 
+	tempDir, err := ioutil.TempDir("", "garble-build")
+	if err != nil {
+		return nil, err
+	}
+	deferred = append(deferred, func() error {
+		return os.RemoveAll(tempDir)
+	})
+	// Add our temporary dir to the beginning of -trimpath, so that we don't
+	// leak temporary dirs. Needs to be at the beginning, since there may be
+	// shorter prefixes later in the list, such as $PWD if TMPDIR=$PWD/tmp.
+	flags = flagSetValue(flags, "-trimpath", tempDir+"=>;"+trimpath)
+	// log.Println(flags)
 	args = flags
-	for _, file := range files {
+	// TODO: randomize the order and names of the files
+	for i, file := range files {
 		file := transformGo(file, info)
-		f, err := ioutil.TempFile("", "garble")
+		tempFile := filepath.Join(tempDir, fmt.Sprintf("z%d.go", i))
+		f, err := os.Create(tempFile)
 		if err != nil {
 			return nil, err
 		}
@@ -212,9 +226,6 @@ func transformCompile(args []string) ([]string, error) {
 		if err := f.Close(); err != nil {
 			return nil, err
 		}
-		deferred = append(deferred, func() error {
-			return os.Remove(f.Name())
-		})
 		args = append(args, f.Name())
 	}
 	return args, nil
@@ -397,3 +408,31 @@ func flagValue(flags []string, name string) string {
 	}
 	return ""
 }
+
+func flagSetValue(flags []string, name, value string) []string {
+	for i, arg := range flags {
+		if strings.HasPrefix(arg, name+"=") {
+			// -name=value
+			if value == "true" {
+				flags[i] = name
+			} else {
+				flags[i] = name + "=" + value
+			}
+			return flags
+		}
+		if arg == name {
+			if i+1 < len(flags) {
+				if val := flags[i+1]; !strings.HasPrefix(val, "-") {
+					flags[i+1] = value
+					return flags
+				}
+			}
+			// -name, equivalent to -name=true
+			if value != "true" {
+				flags[i] = name + "=" + value
+			}
+			return flags
+		}
+	}
+	return append(flags, name+"="+value)
+}

main_test.go

@@ -7,6 +7,7 @@ import (
 	"flag"
 	"fmt"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"regexp"
 	"runtime"
@@ -95,7 +96,14 @@ func bincmp(ts *testscript.TestScript, neg bool, args []string) {
 	data1 := ts.ReadFile(args[0])
 	data2 := ts.ReadFile(args[1])
 	if data1 != data2 {
+		if _, err := exec.LookPath("diffoscope"); err != nil {
+			ts.Logf("diffoscope is not installing; skipping binary diff")
+		} else {
+			// We'll error below; ignore the exec error here.
+			ts.Exec("diffoscope", ts.MkAbs(args[0]), ts.MkAbs(args[1]))
+		}
 		sizeDiff := len(data2) - len(data1)
-		ts.Fatalf("%s and %s differ; size diff: %+d", args[0], args[1], sizeDiff)
+		ts.Fatalf("%s and %s differ; diffoscope above, size diff: %+d",
+			args[0], args[1], sizeDiff)
 	}
 }

testdata/scripts/basic.txt

@@ -26,11 +26,13 @@ cmp stderr main.stderr
 
 ! bingrep main$exe ${WORK@R} 'globalVar' 'globalFunc'
 
-# Finally, check that the 'garble build' shortcut works.
-# cp main main_old
+# Finally, check that the 'garble build' shortcut works, and produces the same
+# binary.
+cp main main_old
+rm main
 garble build main.go
 ! bingrep main$exe 'globalVar'
-# bincmp main main_old
+bincmp main main_old
 
 -- main.go --
 package main

testdata/scripts/imports.txt

@@ -4,6 +4,12 @@ cmp stdout main.stdout
 
 ! bingrep main$exe 'ImportedVar' 'ImportedConst' 'ImportedFunc' 'ImportedType'
 
+# Also check that the binary is reproducible when many imports are involved.
+cp main main_old
+rm main
+garble build
+bincmp main main_old
+
 -- go.mod --
 module foo.com/main
 -- main.go --