reverse lone filenames as well

I've wanted this to more easily debug build failures.

To not force a build failure in a test script, as that would require
some trickery to remain stable, we use runtime.Caller without printing
the line number. Before this patch, those filenames without line numbers
would not be reversed at all.

reverse.go

@@ -110,21 +110,29 @@ func commandReverse(args []string) error {
 					}
 
 				case *ast.CallExpr:
-					// continues below
+					// Reverse position information of call sites.
-				default:
-					return true
-				}
-
-				// Reverse position information.
 					pos := fset.Position(node.Pos())
 					origPos := fmt.Sprintf("%s:%d", goFile, pos.Offset)
-				newPos := hashWith(lpkg.GarbleActionID, origPos) + ".go:1"
+					newFilename := hashWith(lpkg.GarbleActionID, origPos) + ".go"
 
+					// Do "obfuscated.go:1", corresponding to the call site's line.
+					// Most common in stack traces.
 					replaces = append(replaces,
-					newPos,
+						newFilename+":1",
 						fmt.Sprintf("%s/%s:%d", lpkg.ImportPath, goFile, pos.Line),
 					)
 
+					// Do "obfuscated.go" as a fallback.
+					// Most useful in build errors in obfuscated code,
+					// since those might land on any line.
+					// Any ":N" line number will end up being useless,
+					// but at least the filename will be correct.
+					replaces = append(replaces,
+						newFilename,
+						fmt.Sprintf("%s/%s", lpkg.ImportPath, goFile),
+					)
+				}
+
 				return true
 			})
 		}

testdata/scripts/reverse.txt

@@ -56,12 +56,17 @@ package main
 
 import (
 	"os"
+	"runtime"
 
 	"test/main/lib"
 )
 
 func main() {
 	unexportedMainFunc()
+
+	_, filename, _, _ := runtime.Caller(0)
+	println()
+	println("main filename:", filename)
 }
 
 func unexportedMainFunc() {
@@ -79,12 +84,17 @@ package lib
 import (
 	"io"
 	"regexp"
+	"runtime"
 	"runtime/debug"
 )
 
 type ExportedLibType struct{}
 
 func (*ExportedLibType) ExportedLibMethod(w io.Writer) error {
+	_, filename, _, _ := runtime.Caller(0)
+	println("lib filename:", filename)
+	println()
+
 	return printStackTrace(w)
 }
 
@@ -121,19 +131,23 @@ var _ = reflect.TypeOf(UnobfuscatedStruct{})
 
 var _ = struct{SomeField int}(UnobfuscatedStruct{})
 -- reverse.stdout --
+lib filename: test/main/lib/lib.go
+
 goroutine 1 [running]:
 runtime/debug.Stack(0x??, 0x??, 0x??)
 	runtime/debug/stack.go:24 +0x??
 test/main/lib.printStackTrace(0x??, 0x??, 0x??, 0x??)
-	test/main/lib/lib.go:23 +0x??
+	test/main/lib/lib.go:28 +0x??
-test/main/lib.(*ExportedLibType).ExportedLibMethod(...)
+test/main/lib.(*ExportedLibType).ExportedLibMethod(0x??, 0x??, 0x??, 0x??, 0x??)
-	test/main/lib/lib.go:12
+	test/main/lib/lib.go:17 +0x??
-main.unexportedMainFunc.func1()
+main.unexportedMainFunc.func1(...)
-	test/main/main.go:16 +0x??
+	test/main/main.go:21
 main.unexportedMainFunc()
-	test/main/main.go:20 +0x??
+	test/main/main.go:25 +0x??
 main.main()
-	test/main/main.go:10 +0x??
+	test/main/main.go:11 +0x??
+
+main filename: test/main/main.go
 -- build-error-reverse.stdout --
 # test/main/build-error
 test/main/build-error/error.go:18: cannot convert UnobfuscatedStruct{} (type UnobfuscatedStruct) to type struct { SomeField int }