Introduce a limit on the depth of the template instantiation backtrace

we will print with each error that occurs during template
instantiation. When the backtrace is longer than that, we will print
N/2 of the innermost backtrace entries and N/2 of the outermost
backtrace entries, then skip the middle entries with a note such as:

  note: suppressed 2 template instantiation contexts; use
  -ftemplate-backtrace-limit=N to change the number of template
  instantiation entries shown

This should eliminate some excessively long backtraces that aren't
providing any value.

llvm-svn: 101882

1 files changed, 6 insertions, 4 deletions

diff --git a/clang/test/SemaTemplate/instantiation-depth.cpp b/clang/test/SemaTemplate/instantiation-depth.cpp
index f48ede9c44c..20a5c2431b6 100644
--- a/clang/test/SemaTemplate/instantiation-depth.cpp
+++ b/clang/test/SemaTemplate/instantiation-depth.cpp
@@ -1,8 +1,10 @@
-// RUN: %clang_cc1 -fsyntax-only -ftemplate-depth 5 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -verify -ftemplate-depth 5 -ftemplate-backtrace-limit 4 %s
 
-template<typename T> struct X : X<T*> { }; // expected-error{{recursive template instantiation exceeded maximum depth of 5}} \
-// expected-note{{use -ftemplate-depth-N to increase recursive template instantiation depth}} \
-// expected-note 5 {{instantiation of template class}}
+template<typename T> struct X : X<T*> { }; \
+// expected-error{{recursive template instantiation exceeded maximum depth of 5}} \
+// expected-note 3 {{instantiation of template class}} \
+// expected-note {{suppressed 2 template instantiation contexts}} \
+// expected-note {{use -ftemplate-depth-N to increase recursive template instantiation depth}}
 
 void test() { 
   (void)sizeof(X<int>); // expected-note {{instantiation of template class}}