cmd/cgo: add -trimpath flag allowing paths to be rewritten in outputs

cmd/cgo now has a -trimpath flag that behaves the same as the
-trimpath flag to cmd/compile. This will be used to correct paths
to cgo files that are overlaid.

The code that processes trimpath in internal/objapi has been slightly
refactored because it's currently only accessible via AbsFile, which
does some additional processing to the path names. Now an
ApplyRewrites function is exported that just applies the trimpath
rewrites.

Also remove unused srcfile argument to cmd/cgo.(*Package).godefs.

For #39958

Change-Id: I497d48d0bc2fe1f6ab2b5835cbe79f15b839ee59
Reviewed-on: https://go-review.googlesource.com/c/go/+/266358
Trust: Michael Matloob <matloob@golang.org>
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/src/cmd/cgo/main.go b/src/cmd/cgo/main.go
index 7d02ac3c54..c1116e28ec 100644
--- a/src/cmd/cgo/main.go
+++ b/src/cmd/cgo/main.go
@@ -243,6 +243,8 @@ var gccgopkgpath = flag.String("gccgopkgpath", "", "-fgo-pkgpath option used wit
 var gccgoMangler func(string) string
 var importRuntimeCgo = flag.Bool("import_runtime_cgo", true, "import runtime/cgo in generated code")
 var importSyscall = flag.Bool("import_syscall", true, "import syscall in generated code")
+var trimpath = flag.String("trimpath", "", "applies supplied rewrites or trims prefixes to recorded source file paths")
+
 var goarch, goos string
 
 func main() {
@@ -322,6 +324,13 @@ func main() {
 			input = filepath.Join(*srcDir, input)
 		}
 
+		// Create absolute path for file, so that it will be used in error
+		// messages and recorded in debug line number information.
+		// This matches the rest of the toolchain. See golang.org/issue/5122.
+		if aname, err := filepath.Abs(input); err == nil {
+			input = aname
+		}
+
 		b, err := ioutil.ReadFile(input)
 		if err != nil {
 			fatalf("%s", err)
@@ -330,6 +339,10 @@ func main() {
 			fatalf("%s", err)
 		}
 
+		// Apply trimpath to the file path. The path won't be read from after this point.
+		input, _ = objabi.ApplyRewrites(input, *trimpath)
+		goFiles[i] = input
+
 		f := new(File)
 		f.Edit = edit.NewBuffer(b)
 		f.ParseGo(input, b)
@@ -367,7 +380,7 @@ func main() {
 		p.PackagePath = f.Package
 		p.Record(f)
 		if *godefs {
-			os.Stdout.WriteString(p.godefs(f, input))
+			os.Stdout.WriteString(p.godefs(f))
 		} else {
 			p.writeOutput(f, input)
 		}