[lld][ELF] Only convert dependency filename to native form on Windows

Currently, llvm::sys::path::native is used unconditionally when
generating dependency filenames. This is correct on Windows, where
backslashes are valid path separators, but can be incorrect on
non-Windows platforms, because in that case backslashes in the
filenames are converted to forward slashes, while they should be treated
as ordinary characters.

This fixes the following inconsistency between ld.lld and ld.bfd:

    $ cat test.s
    .globl _start
    _start:
    $ cc -c test.s -o "back\\slash.o"
    $ ld.lld -o test "back\\slash.o" --dependency-file=/dev/stdout
    test: \
     back/slash.o

    back/slash.o:
    $ ld.bfd -o test "back\\slash.o" --dependency-file=/dev/stdout
    test: \
      back\slash.o

    back\slash.o:

In addition, while we're here, use 2-space indentation when printing out
dependency filenames (consistent with Clang and ld.bfd), and escape the
filename of the target (output file) too.

Signed-off-by: Ruoyu Zhong <[email protected]>

Author: ZhongRuoyu

lld/ELF/Driver.cpp

@@ -2482,10 +2482,14 @@ static void writeDependencyFile(Ctx &ctx) {
   // We use the same escape rules as Clang/GCC which are accepted by Make/Ninja:
   // * A space is escaped by a backslash which itself must be escaped.
   // * A hash sign is escaped by a single backslash.
-  // * $ is escapes as $$.
+  // * $ is escaped as $$.
   auto printFilename = [](raw_fd_ostream &os, StringRef filename) {
     llvm::SmallString<256> nativePath;
+#ifdef _WIN32
     llvm::sys::path::native(filename.str(), nativePath);
+#else
+    nativePath = filename;
+#endif
     llvm::sys::path::remove_dots(nativePath, /*remove_dot_dot=*/true);
     for (unsigned i = 0, e = nativePath.size(); i != e; ++i) {
       if (nativePath[i] == '#') {
@@ -2502,9 +2506,10 @@ static void writeDependencyFile(Ctx &ctx) {
     }
   };
 
-  os << ctx.arg.outputFile << ":";
+  printFilename(os, ctx.arg.outputFile);
+  os << ":";
   for (StringRef path : ctx.arg.dependencyFiles) {
-    os << " \\\n ";
+    os << " \\\n  ";
     printFilename(os, path);
   }
   os << "\n";

lld/test/ELF/dependency-file-backslash-as-normal-char.s

@@ -0,0 +1,13 @@
+# REQUIRES: x86, !system-windows
+# RUN: mkdir -p %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o "%t/back\\slash.o"
+# RUN: ld.lld -o %t/foo.exe "%t/back\\slash.o" --dependency-file=%t/foo.d
+# RUN: FileCheck --match-full-lines -DFILE=%t %s < %t/foo.d
+
+# CHECK:      [[FILE]]/foo.exe: \
+# CHECK-NEXT:   [[FILE]]/back\slash.o
+# CHECK-EMPTY:
+# CHECK-NEXT: [[FILE]]/back\slash.o:
+
+.global _start
+_start:

lld/test/ELF/dependency-file-backslash-as-path-separator.s

@@ -0,0 +1,13 @@
+# REQUIRES: x86, system-windows
+# RUN: mkdir -p %t/back
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o "%t/back\\slash.o"
+# RUN: ld.lld -o %t/foo.exe "%t/back\\slash.o" --dependency-file=%t/foo.d
+# RUN: FileCheck --match-full-lines -DFILE=%t %s < %t/foo.d
+
+# CHECK:      [[FILE]]\foo.exe: \
+# CHECK-NEXT:   [[FILE]]\back\slash.o
+# CHECK-EMPTY:
+# CHECK-NEXT: [[FILE]]\back\slash.o:
+
+.global _start
+_start: