Support both -arg and /arg with msvc/clang-cl without altering paths

[glandium]

34c6f9a added support for /arg flags by replacing the initial slash with
a -, and falling back to normal argument parsing. Unfortunately, when
running clang-cl on a non-Windows system, that means absolute paths get
garbled, and that can lead to bad argument parsing with separate
arguments (e.g. -I /absolute/path).

We change the arguments definition for MSVC to include both styles, by
hacking up a macro that generates two lists, one with - arguments, and
one with / arguments. Merging the two lists at build time doesn't seem
possible without going full procedural macro.

Fixes #669

[emilio]

Merging the two lists at build time doesn't seem
possible without going full procedural macro.

Doesn't this achieve what you want?

diff --git a/src/compiler/msvc.rs b/src/compiler/msvc.rs
index 3302856..7197b8c 100644
--- a/src/compiler/msvc.rs
+++ b/src/compiler/msvc.rs
@@ -229,8 +229,10 @@ use self::ArgData::*;
 
 macro_rules! msvc_args {
     (static ARGS: [$t:ty; _] = [$($macro:ident ! ($($v:tt)*),)*]) => {
-        counted_array!(static ARGS: [$t; _] = [$(msvc_args!(@one "-", $macro!($($v)*)),)*]);
-        counted_array!(static SLASH_ARGS: [$t; _] = [$(msvc_args!(@one "/", $macro!($($v)*)),)*]);
+        counted_array!(static ARGS: [$t; _] = [
+            $(msvc_args!(@one "-", $macro!($($v)*)),)*
+            $(msvc_args!(@one "/", $macro!($($v)*)),)*
+        ]);
     };
     (@one $prefix:expr, msvc_take_arg!($s:expr, $($t:tt)*)) => {
         take_arg!(concat!($prefix, $s), $($t)+)
@@ -284,7 +286,7 @@ pub fn parse_arguments(
     let mut show_includes = false;
     let mut xclangs: Vec<OsString> = vec![];
 
-    for arg in ArgsIter::new(arguments.iter().cloned(), (&ARGS[..], &SLASH_ARGS[..])) {
+    for arg in ArgsIter::new(arguments.iter().cloned(), &ARGS[..]) {
         let arg = try_or_cannot_cache!(arg, "argument parse");
         match arg.get_data() {
             Some(TooHardFlag) | Some(TooHard(_)) | Some(TooHardPath(_)) => {

[froydnj]

This doesn't work because of the requirement of ARGS to be sorted. (I'm having trouble figuring out where we actually use this fact, but glandium pointed out the same thing to me when I made this argument last night and we do have tests for non-sorted arg arrays panic'ing, so I assume it must make a difference somewhere...)

[glandium]

We're using a binary search in args.rs, which requires the list to be sorted. @emilio's diff would work if there wasn't the "@" argument. I tried something similar to that diff with a scheme to eliminate non-msvc_* arguments in prefixed passes and a final non-prefixed pass without the msvc_* arguments, but all I ended up with was this tweet: https://twitter.com/MikeHommey/status/1232932709409771522

[peterjc123]

Caching is broken for commands like cl /c /EHsc a.cpp after this PR.
Related log:

DEBUG 2020-04-16T08:04:08Z: sccache::server: handle_client: compile
DEBUG 2020-04-16T08:04:08Z: sccache::server: check_compiler: Supported compiler
DEBUG 2020-04-16T08:04:08Z: sccache::server: parse_arguments: CannotCache(multiple input files): ["/c", "/EHsc", "a.cpp"]

But if I change to cl /c -EHsc a.cpp, it is working.

DEBUG 2020-04-16T08:02:45Z: sccache::server: handle_client: compile
DEBUG 2020-04-16T08:02:45Z: sccache::server: check_compiler: Supported compiler
DEBUG 2020-04-16T08:02:45Z: sccache::server: parse_arguments: Ok: ["/c", "-EHsc", "a.cpp"]
DEBUG 2020-04-16T08:02:45Z: sccache::compiler::compiler: [a.obj]: get_cached_or_compile: ["/c", "-EHsc", "a.cpp"]
DEBUG 2020-04-16T08:02:45Z: sccache::compiler::msvc: preprocess: Some("C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Enterprise\\VC\\Tools\\MSVC\\14.16.27023\\bin\\HostX64\\x64\\cl.EXE" "-E" "a.cpp" "-nologo" "-EHsc")
DEBUG 2020-04-16T08:02:45Z: sccache::compiler::compiler: [a.obj]: generate_hash_key took 0.232 s

[glandium]

Please open a new issue.

[peterjc123]

@glandium No problem.