[lld-macho] Add option --error-limit=N

[gkm]

Summary

Add option to limit (or remove limits) on the number of errors printed before exiting. This option exists in the other lld ports: COFF & ELF.

[int3]

lgtm

lld/MachO/Driver.cpp

bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
 
   errorHandler().logName = args::getFilenameWithoutExe(argsArr[0]);
   stderrOS.enable_colors(stderrOS.has_colors());
   // TODO: Set up error handler properly, e.g. the errorLimitExceededMsg
 
   MachOOptTable parser;
   InputArgList args = parser.parse(argsArr.slice(1));
 
+  errorHandler().errorLimitExceededMsg =
+      "too many errors emitted, stopping now "
+      "(use --error-limit=0 to see all errors)";
+  errorHandler().errorLimit = args::getInteger(args, OPT_error_limit_eq, 20);
+
   if (args.hasArg(OPT_help_hidden)) {
     parser.printHelp(argsArr[0], /*showHidden=*/true);
     return true;
   }
   if (args.hasArg(OPT_help)) {
     parser.printHelp(argsArr[0], /*showHidden=*/false);
     return true;
   }

lld/MachO/Options.td

 include "llvm/Option/OptParser.td"
 
 // Flags that lld/MachO understands but ld64 doesn't. These take
 // '--' instead of '-' and use dashes instead of underscores, so
 // they don't collide with the ld64 compat options.
 def grp_lld : OptionGroup<"kind">, HelpText<"LLD-SPECIFIC">;
 
 def help : Flag<["-", "--"], "help">,
     Group<grp_lld>;
 def help_hidden : Flag<["--"], "help-hidden">,
     HelpText<"Display help for hidden options">,
     Group<grp_lld>;
+def error_limit_eq : Joined<["--"], "error-limit=">,
+    HelpText<"Maximum number of errors to print before exiting (default: 20)">,
+    Group<grp_lld>;
 def color_diagnostics: Flag<["--"], "color-diagnostics">,
     HelpText<"Alias for --color-diagnostics=always">,
     Group<grp_lld>;
 def no_color_diagnostics: Flag<["--"], "no-color-diagnostics">,
     HelpText<"Alias for --color-diagnostics=never">,
     Group<grp_lld>;
 def color_diagnostics_eq: Joined<["--"], "color-diagnostics=">,
     HelpText<"Use colors in diagnostics (default: auto)">,

lld/test/MachO/error-limit.test

+## Check that we only see 20 (the default error-limit) "cannot open" errors
+RUN: not %lld A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 2>&1 | \
+RUN:     FileCheck -check-prefix=DEFAULT %s
+
+DEFAULT:      cannot open A:
+DEFAULT:      cannot open T:
+DEFAULT-NOT:  cannot open U:
+DEFAULT-NEXT: too many errors emitted, stopping now (use --error-limit=0 to see all errors)
+
+## Check that we only see 5 "cannot open" errors when --error-limit=5
+RUN: not %lld --error-limit=5 A B C D E F G H I J 2>&1 \
+RUN:   | FileCheck -check-prefix=LIMIT5 %s
+
+LIMIT5:      cannot open A:
+LIMIT5:      cannot open E:
+LIMIT5-NOT:  cannot open F:
+LIMIT5-NEXT: too many errors emitted, stopping now (use --error-limit=0 to see all errors)
+
+## Check that we see all "cannot open" errors when --error-limit=0 (unimited)
+RUN: not %lld --error-limit=0 A B C D E F G H I J K L M N O P Q R S T U V W 2>&1 | \
+RUN:     FileCheck -check-prefix=UNLIMITED %s
+
+UNLIMITED:     cannot open A:
+UNLIMITED:     cannot open T:
+UNLIMITED:     cannot open U:
+UNLIMITED:     cannot open V:
+UNLIMITED:     cannot open W:
+UNLIMITED-NOT: too many errors emitted, stopping now (use --error-limit=0 to see all errors)