add a new driver-level -ferror-limit=412 option, which causes clang to stop
emitting diagnostics after it has produced that many errors.  Give this a
default value of 20 which produces plenty of errors for people to fix before
recompiling but not so many that their entire console scrolls away when the
compiler gets confused.  The experience looks like this:

$ clang foo.c
<tons of crap>
foo.c:102:3: error: unknown type name 'somethingbad'
  somethingbad x;
  ^
fatal error: too many errors emitted, stopping now
36 warnings and 20 errors generated.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@100689 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/UsersManual.html b/docs/UsersManual.html
index e7ea133..f6651b1 100644
--- a/docs/UsersManual.html
+++ b/docs/UsersManual.html
@@ -189,6 +189,10 @@
 <p><b>-pedantic-errors</b>: Error on language extensions.</p>
 <p><b>-Wsystem-headers</b>: Enable warnings from system headers.</p>
 
+<p><b>-ferror-limit=123</b>: Stop emitting diagnostics after 123 errors have
+   been produced.  The default is 20, and the error limit can be disabled with
+   -ferror-limit=0.</p>
+
 <!-- ================================================= -->
 <h4 id="cl_diag_formatting">Formatting of Diagnostics</h4>
 <!-- ================================================= -->
diff --git a/include/clang/Driver/Options.td b/include/clang/Driver/Options.td
index ed68d68..dd4586e 100644
--- a/include/clang/Driver/Options.td
+++ b/include/clang/Driver/Options.td
@@ -356,6 +356,7 @@
 def fstrict_aliasing : Flag<"-fstrict-aliasing">, Group<clang_ignored_f_Group>;
 def fsyntax_only : Flag<"-fsyntax-only">, Flags<[DriverOption]>;
 def ftabstop_EQ : Joined<"-ftabstop=">, Group<f_Group>;
+def ferror_limit_EQ : Joined<"-ferror-limit=">, Group<f_Group>;
 def ftemplate_depth_ : Joined<"-ftemplate-depth-">, Group<f_Group>;
 def fterminated_vtables : Flag<"-fterminated-vtables">, Group<f_Group>;
 def fthreadsafe_statics : Flag<"-fthreadsafe-statics">, Group<f_Group>;
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index 2a37991..cd38c4d 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -1073,6 +1073,12 @@
     CmdArgs.push_back(A->getValue(Args));
   }
 
+  CmdArgs.push_back("-ferror-limit");
+  if (Arg *A = Args.getLastArg(options::OPT_ferror_limit_EQ))
+    CmdArgs.push_back(A->getValue(Args));
+  else
+    CmdArgs.push_back("19");
+  
   // Pass -fmessage-length=.
   CmdArgs.push_back("-fmessage-length");
   if (Arg *A = Args.getLastArg(options::OPT_fmessage_length_EQ)) {