[llvm-windres] Implement the windres flag --use-temp-file

Whether a temp file or a pipe is used for preprocessing is an
internal detail, this flag has a notable effect on the preprocessing
in GNU windres. Without this flag, GNU windres passes command
arguments as-is to popen(), which means they get evaluated by a
shell without being re-escaped for this case. To mimic this,
llvm-windres has manually tried to unescape arguments.

When GNU windres is given the --use-temp-file flag, it uses a
different API for invoking the preprocessor, and this API takes care
of preserving special characters in the command line arguments.
For users of GNU windres, this means that by using --use-temp-file,
they don't need to do the (quite terrible) double escaping of
quotes/spaces etc.

The xz project uses the --use-temp-file flag when invoking
GNU windres, see
https://github.com/tukaani-project/xz/commit/6b117d3b1fe91eb26d533ab16a2e552f84148d47.
However as llvm-windres didn't implement this flag and just
assumed the GNU windres popen() behaviour, they had to use a
different codepath for llvm-windres.

That separate codepath for llvm-windres broke later when llvm-windres
got slightly more accurate unescaping of lone quotes in
0f4c6b120f21d582ab7c5c4f2b2a475086c34938 /
https://reviews.llvm.org/D146848 (fixing a discrepancy to GNU
windres as found in https://github.com/llvm/llvm-project/issues/57334),
and this was reported in
https://github.com/mstorsjo/llvm-mingw/issues/363.

Not touching the implementation of the --preprocessor option
with respect to the --use-temp-file flag; that option is doubly
tricky as GNU windres changed its behaviour in a backwards incompatible
way recently (and llvm-windres currently matches the old behaviour).
(See
https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=21c33bcbe36377abf01614fb1b9be439a3b6de20,
https://sourceware.org/bugzilla/show_bug.cgi?id=27594 and
https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=5edb8e3f5ad8d74a83fc0df7f6e4514eed0aa77f;hp=3abbafc2aacc6706fea3e3e326e2f08d107c3672
for the behaviour change.)

Differential Revision: https://reviews.llvm.org/D159223

1 files changed, 13 insertions, 4 deletions

diff --git a/llvm/tools/llvm-rc/llvm-rc.cpp b/llvm/tools/llvm-rc/llvm-rc.cpp
index e5bf623..b955347f 100644
--- a/llvm/tools/llvm-rc/llvm-rc.cpp
+++ b/llvm/tools/llvm-rc/llvm-rc.cpp
@@ -461,7 +461,14 @@ RcOptions parseWindresOptions(ArrayRef<const char *> ArgsArr,
     // done this double escaping) probably is confined to cases like these
     // quoted string defines, and those happen to work the same across unix
     // and windows.
-    std::string Unescaped = unescape(Arg->getValue());
+    //
+    // If GNU windres is executed with --use-temp-file, it doesn't use
+    // popen() to invoke the preprocessor, but uses another function which
+    // actually preserves tricky characters better. To mimic this behaviour,
+    // don't unescape arguments here.
+    std::string Value = Arg->getValue();
+    if (!InputArgs.hasArg(WINDRES_use_temp_file))
+      Value = unescape(Value);
     switch (Arg->getOption().getID()) {
     case WINDRES_include_dir:
       // Technically, these are handled the same way as e.g. defines, but
@@ -475,17 +482,19 @@ RcOptions parseWindresOptions(ArrayRef<const char *> ArgsArr,
       break;
     case WINDRES_define:
       Opts.PreprocessArgs.push_back("-D");
-      Opts.PreprocessArgs.push_back(Unescaped);
+      Opts.PreprocessArgs.push_back(Value);
       break;
     case WINDRES_undef:
       Opts.PreprocessArgs.push_back("-U");
-      Opts.PreprocessArgs.push_back(Unescaped);
+      Opts.PreprocessArgs.push_back(Value);
       break;
     case WINDRES_preprocessor_arg:
-      Opts.PreprocessArgs.push_back(Unescaped);
+      Opts.PreprocessArgs.push_back(Value);
       break;
     }
   }
+  // TODO: If --use-temp-file is set, we shouldn't be unescaping
+  // the --preprocessor argument either, only splitting it.
   if (InputArgs.hasArg(WINDRES_preprocessor))
     Opts.PreprocessCmd =
         unescapeSplit(InputArgs.getLastArgValue(WINDRES_preprocessor));