[LLD][MinGW] Add --error-limit=<N> option

[alvinhochun]

Summary

This maps to -errorlimit:<N> in the COFF linker and is functionally
identical to the same option in the ELF and MachO linker.

[mstorsjo]

Looks fine to me overall, one minor nit to address, and a little discussion on some details.

lld/MinGW/Driver.cpp

397

It's somewhat unusual to interpret the argument values that much in the mingw driver (except in the cases where they need to be rewritten), but I see the intent of making the error message mention the right name - so it's probably fine.

(Technically I guess we have that issue for any other argument too, where we just pass values on blindly, and the COFF linker may complain about their values later on.)

lld/test/MinGW/error-limit.test

12

I think it'd be nice with a : after the option name here; in the case of the COFF driver, the option name itself contains it so there's no need, but e.g. the ELF linker seems to manually add it in some similar cases.

14

I think we don't have any lld mingw driver tests that actually invoke the coff linker, all of them just use -### to see what it outputs. Strictly speaking, we tend to avoid such tests, although this one seems harmless (although kinda redundant, as this gets covered in total by the other testcases too)?

[alvinhochun]

Added : in the error message and removed a redundant test in MinGW/error-limit.test

lld/COFF/Driver.cpp

void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   if (args.hasArg(OPT_dash_dash_version)) {
     message(getLLDVersion());
     return;
   }
 
   // Handle /lldmingw early, since it can potentially affect how other
   // options are handled.
   config->mingw = args.hasArg(OPT_lldmingw);
+  if (config->mingw)
+    ctx.e.errorLimitExceededMsg = "too many errors emitted, stopping now"
+                                  " (use --error-limit=0 to see all errors)";
 
   // Handle /linkrepro and /reproduce.
   if (Optional<std::string> path = getReproduceFile(args)) {
     Expected<std::unique_ptr<TarWriter>> errOrWriter =
         TarWriter::create(*path, sys::path::stem(*path));
 
     if (errOrWriter) {
       tar = std::move(*errOrWriter);

lld/MinGW/Driver.cpp

if (args.hasFlag(OPT_guard_cf, OPT_no_guard_cf, false)) {
     else
       add("-guard:cf,nolongjmp");
   } else if (args.hasFlag(OPT_guard_longjmp, OPT_no_guard_longjmp, false)) {
     auto *a = args.getLastArg(OPT_guard_longjmp);
     warn("parameter " + a->getSpelling() +
          " only takes effect when used with --guard-cf");
   }
 
+  if (auto *a = args.getLastArg(OPT_error_limit)) {
+    int n;
+    StringRef s = a->getValue();
+    if (s.getAsInteger(10, n))
+      error(a->getSpelling() + " number expected, but got " + s);
+    else
+      add("-errorlimit:" + s);
+  }
+
   for (auto *a : args.filtered(OPT_mllvm))
     add("-mllvm:" + StringRef(a->getValue()));
 
   for (auto *a : args.filtered(OPT_Xlink))
     add(a->getValue());
 
   if (args.getLastArgValue(OPT_m) == "i386pe")
     add("-alternatename:__image_base__=___ImageBase");

lld/MinGW/Options.td

 defm thinlto_cache_dir: EqLong<"thinlto-cache-dir",
   "Path to ThinLTO cached object file directory">;
 defm Xlink : Eq<"Xlink", "Pass <arg> to the COFF linker">, MetaVarName<"<arg>">;
 defm guard_cf : B<"guard-cf", "Enable Control Flow Guard" ,
   "Do not enable Control Flow Guard (default)">;
 defm guard_longjmp : B<"guard-longjmp",
   "Enable Control Flow Guard long jump hardening (default for --guard-cf)" ,
   "Do not enable Control Flow Guard long jump hardening">;
+defm error_limit:
+  EqLong<"error-limit", "Maximum number of errors to emit before stopping (0 = no limit)">;
 
 // Alias
 def alias_Bdynamic_call_shared: Flag<["-"], "call_shared">, Alias<Bdynamic>;
 def alias_Bdynamic_dy: Flag<["-"], "dy">, Alias<Bdynamic>;
 def alias_Bstatic_dn: Flag<["-"], "dn">, Alias<Bstatic>;
 def alias_Bstatic_non_shared: Flag<["-"], "non_shared">, Alias<Bstatic>;
 def alias_Bstatic_static: Flag<["-"], "static">, Alias<Bstatic>;
 def alias_entry_e: JoinedOrSeparate<["-"], "e">, Alias<entry>;

lld/test/COFF/error-limit.test

 UNLIMITED:     could not open '21'
 UNLIMITED:     could not open '22'
 UNLIMITED-NOT: too many errors emitted, stopping now (use /errorlimit:0 to see all errors)
 
 RUN: not lld-link /errorlimit:XYZ 01 02 03 04 05 06 07 08 09 10 11 12 13 14 \
 RUN:   15 16 17 18 19 20 21 22 2>&1 | FileCheck -check-prefix=WRONG %s
 
 WRONG:      /errorlimit: number expected, but got XYZ
+
+RUN: not lld-link -lldmingw 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 \
+RUN:   21 22 2>&1 | FileCheck -check-prefix=MINGW-DEFAULT %s
+
+MINGW-DEFAULT:      could not open '01'
+MINGW-DEFAULT:      could not open '20'
+MINGW-DEFAULT-NEXT: too many errors emitted, stopping now (use --error-limit=0 to see all errors)
+MINGW-DEFAULT-NOT:  could not open '21'

lld/test/MinGW/error-limit.test

+RUN: ld.lld -### foo.o -m i386pep 2>&1 | FileCheck -check-prefix=DEFAULT %s
+DEFAULT-NOT: -errorlimit:
+DEFAULT-NOT: /errorlimit:
+
+RUN: ld.lld -### foo.o -m i386pep --error-limit=5 2>&1 | FileCheck -check-prefix=NUMERIC %s
+NUMERIC: -errorlimit:5
+
+RUN: ld.lld -### foo.o -m i386pep --error-limit=0 2>&1 | FileCheck -check-prefix=UNLIMITED %s
+UNLIMITED: -errorlimit:0
+
+RUN: not ld.lld -### foo.o -m i386pep --error-limit=XYZ 2>&1 | FileCheck -check-prefix=WRONG %s
+WRONG:      --error-limit number expected, but got XYZ
+
+RUN: not ld.lld -m i386pep --error-limit=5 01 02 03 04 05 06 07 08 09 10 2>&1 \
+RUN:   | FileCheck -check-prefix=LIMIT5 %s
+LIMIT5:      could not open '01'
+LIMIT5:      could not open '05'
+LIMIT5-NEXT: too many errors emitted, stopping now (use --error-limit=0 to see all errors)
+LIMIT5-NOT:  could not open '06'