Don't fail the shared_ptr test if libc++ has insufficient debug info.

[saugustine]

Summary

Don't fail the shared_ptr test if libc++ has insufficient debug info.

This addresses https://bugs.llvm.org/show_bug.cgi?id=48937

[dblaikie]

Generally makes sense to me - I'd probably lean on this being a bit too narrow (but if it handles the current cases, we can generalize if/when needed), in that it'll be a bit brittle to changes to libc++. Well, I guess if anything's renamed, or moved into the libc++ library it'll require touching the pretty printer anyway.

Ah, I see - so you're looking for the field which is a member of shared_count - might be good for the comment to have a few more words about what the purpose is there. Connecting the dots between "determine if libc++ itself has debug info" and why this test achieves that result (something like... because shared_count has virtual functions and has its key function defined in the libc++ library, so the type definition will only be emitted there (if libc++ itself is built with debug info) and without the definition the __shared_owners_ field won't be available)

Any sense of the difference between UNSUPPORTED and IGNORED for things like this?

[saugustine]

Dramatically rework the last attempt.

[saugustine]

Thanks for the review. I reworked to take a somewhat different approach--this improves the printer itself to tolerate the situation quite a bit better. But I have included your improved comment at the decision point.

[dblaikie]

Oh, nice improvement! Yeah, the number of bugs we get due to the arbitrary/inscrutible nature of the failure when pretty printing std::string due to this optimization... - hopefully the more scrutible error message will hopefully reduce that and/ror make triage easier when folks do reach out for help.

[ldionne]

LGTM for libc++ if you folks agree this is OK.

[ldionne]

@saugustine Please watch out for your commit messages, they are messed up:

commit 0e8378032597bcaccb948de88e965ad75bfaeb7b
Author: Sterling Augustine <[e-mail]>
Date:   Thu Apr 15 18:03:01 2021 -0700

    Don't fail the shared_ptr test if libc++ has insufficient debug info.

    Don't fail the shared_ptr test if libc++ has insufficient debug info.

    This addresses https://bugs.llvm.org/show_bug.cgi?id=48937

    Differential Revision: https://reviews.llvm.org/D100610

libcxx/test/libcxx/gdb/gdb_pretty_printer_test.py

def invoke(self, arg, from_tty):
             # Use interactive commands in the correct context to get the pretty
             # printed version
 
             value_str = self._get_value_string(compare_frame, testcase_frame)
 
             # Ignore the convenience variable name and newline
             value = value_str[value_str.find("= ") + 2:-1]
             gdb.newest_frame().select()
-
             expectation_val = compare_frame.read_var("expectation")
             check_literal = expectation_val.string(encoding="utf-8")
             if "PrettyPrintToRegex" in compare_frame.name():
                 test_fails = not re.search(check_literal, value)
             else:
                 test_fails = value != check_literal
 
             if test_fails:

libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp

void pointer_negative_test() {
   ComparePrettyPrintToRegex(int_ptr, R"(\(int \*\) 0x[a-f0-9]+)");
 }
 
 void shared_ptr_test() {
   // Shared ptr tests while using test framework call another function
   // due to which there is one more count for the pointer. Hence, all the
   // following tests are testing with expected count plus 1.
   std::shared_ptr<const int> test0 = std::make_shared<const int>(5);
+  // The python regular expression matcher treats newlines as significant, so
+  // these regular expressions should be on one line.
   ComparePrettyPrintToRegex(
       test0,
-      R"(std::shared_ptr<int> count 2, weak 0 containing = {__ptr_ = 0x[a-f0-9]+})");
+      R"(std::shared_ptr<int> count [2\?], weak [0\?]( \(libc\+\+ missing debug info\))? containing = {__ptr_ = 0x[a-f0-9]+})");
 
   std::shared_ptr<const int> test1(test0);
   ComparePrettyPrintToRegex(
       test1,
-      R"(std::shared_ptr<int> count 3, weak 0 containing = {__ptr_ = 0x[a-f0-9]+})");
+      R"(std::shared_ptr<int> count [3\?], weak [0\?]( \(libc\+\+ missing debug info\))? containing = {__ptr_ = 0x[a-f0-9]+})");
 
   {
     std::weak_ptr<const int> test2 = test1;
     ComparePrettyPrintToRegex(
         test0,
-        R"(std::shared_ptr<int> count 3, weak 1 containing = {__ptr_ = 0x[a-f0-9]+})");
+        R"(std::shared_ptr<int> count [3\?], weak [1\?]( \(libc\+\+ missing debug info\))? containing = {__ptr_ = 0x[a-f0-9]+})");
   }
 
   ComparePrettyPrintToRegex(
       test0,
-      R"(std::shared_ptr<int> count 3, weak 0 containing = {__ptr_ = 0x[a-f0-9]+})");
+      R"(std::shared_ptr<int> count [3\?], weak [0\?]( \(libc\+\+ missing debug info\))? containing = {__ptr_ = 0x[a-f0-9]+})");
 
   std::shared_ptr<const int> test3;
   ComparePrettyPrintToChars(test3, "std::shared_ptr is nullptr");
 }
 
 void streampos_test() {
   std::streampos test0 = 67;
   ComparePrettyPrintToChars(

libcxx/utils/gdb/libcxx/printers.py

def to_string(self):
         """Returns self as a string."""
         typename = _remove_generics(_prettify_typename(self.val.type))
         pointee_type = _remove_generics(
             _prettify_typename(self.val.type.template_argument(0)))
         if not self.addr:
             return "%s is nullptr" % typename
         refcount = self.val["__cntrl_"]
         if refcount != 0:
+            try:
                 usecount = refcount["__shared_owners_"] + 1
                 weakcount = refcount["__shared_weak_owners_"]
                 if usecount == 0:
                     state = "expired, weak %d" % weakcount
                 else:
                     state = "count %d, weak %d" % (usecount, weakcount)
+            except:
+                # Debug info for a class with virtual functions is emitted
+                # in the same place as its key function. That means that
+                # for std::shared_ptr, __shared_owners_ is emitted into
+                # into libcxx.[so|a] itself, rather than into the shared_ptr
+                # instantiation point. So if libcxx.so was built without
+                # debug info, these fields will be missing.
+                state = "count ?, weak ? (libc++ missing debug info)"
         return "%s<%s> %s containing" % (typename, pointee_type, state)
 
     def __iter__(self):
         if self.addr:
             yield "__ptr_", self.addr
 
     def children(self):
         return self