Clarify ERR_print_errors_* clear the error queue.

Change-Id: Ifaa0129cbacb2346a8d206436eca783060181a85
Reviewed-on: https://boringssl-review.googlesource.com/20004
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

crypto/test/gtest_main.h

@@ -38,13 +38,14 @@ class ErrorTestEventListener : public testing::EmptyTestEventListener {
   ~ErrorTestEventListener() override {}
 
   void OnTestEnd(const testing::TestInfo &test_info) override {
-    // If the test failed, print any errors left in the error queue.
     if (test_info.result()->Failed()) {
+      // The test failed. Print any errors left in the error queue.
       ERR_print_errors_fp(stdout);
+    } else {
+      // The test succeeded, so any failed operations are expected. Clear the
+      // error queue without printing.
+      ERR_clear_error();
     }
-
-    // Clean up the error queue for the next run.
-    ERR_clear_error();
   }
 };
 

include/openssl/err.h

@@ -224,17 +224,14 @@ OPENSSL_EXPORT const char *ERR_reason_error_string(uint32_t packed_error);
 typedef int (*ERR_print_errors_callback_t)(const char *str, size_t len,
                                            void *ctx);
 
-// ERR_print_errors_cb calls |callback| with a string representation of each
-// error in the current thread's error queue, from the least recent to the most
-// recent error.
+// ERR_print_errors_cb clears the current thread's error queue, calling
+// |callback| with a string representation of each error, from the least recent
+// to the most recent error.
 //
 // The string will have the following format (which differs from
 // |ERR_error_string|):
 //
-//   [thread id]:error:[error code]:[library name]:OPENSSL_internal:
-//   [reason string]:[file]:[line number]:[optional string data]
-//
-// (All in one line.)
+//   [thread id]:error:[error code]:[library name]:OPENSSL_internal:[reason string]:[file]:[line number]:[optional string data]
 //
 // The callback can return one to continue the iteration or zero to stop it.
 // The |ctx| argument is an opaque value that is passed through to the
@@ -242,8 +239,8 @@ typedef int (*ERR_print_errors_callback_t)(const char *str, size_t len,
 OPENSSL_EXPORT void ERR_print_errors_cb(ERR_print_errors_callback_t callback,
                                         void *ctx);
 
-// ERR_print_errors_fp prints the current contents of the error stack to |file|
-// using human readable strings where possible.
+// ERR_print_errors_fp clears the current thread's error queue, printing each
+// error to |file|. See |ERR_print_errors_cb| for the format.
 OPENSSL_EXPORT void ERR_print_errors_fp(FILE *file);