Fix o3tl::string_view streaming operator <<

(The unnecessary os.setstate(std::ios_base::failbit) was due to a misreading of
C++17 [ostream.formatted.reqmts]/1.)

Change-Id: I7d8285230cb316c7af45c76029e9629517d05d56
Reviewed-on: https://gerrit.libreoffice.org/65217
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

include/o3tl/string_view.hxx

@@ -732,12 +732,13 @@ operator <<(
     std::basic_ostream<charT, traits> & os,
     basic_string_view<charT, traits> str)
 {
-    typename std::basic_ostream<charT, traits>::sentry sentry;
+    typename std::basic_ostream<charT, traits>::sentry sentry(os);
     if (sentry) {
         auto const w = os.width();
-        auto const pad
-            = std::max<std::make_unsigned<decltype(w + str.size())>::type>(
-                w < 0 ? 0 : w, str.size());
+        auto pad
+            = std::max<typename std::make_unsigned<decltype(w + str.size())>::type>(
+                  w < 0 ? 0 : w, str.size())
+              - str.size();
         auto const after = (os.flags() & std::ios_base::adjustfield)
             == std::ios_base::left;
         if (pad != 0 && !after) {
@@ -754,8 +755,6 @@ operator <<(
             }
         }
         os.width(0);
-    } else {
-        os.setstate(std::ios_base::failbit);
     }
     return os;
 }

o3tl/qa/test-string_view.cxx

@@ -9,7 +9,9 @@
 
 #include <sal/config.h>
 
+#include <sstream>
 #include <stdexcept>
+#include <string>
 
 #include <cppunit/TestAssert.h>
 #include <cppunit/TestFixture.h>
@@ -27,6 +29,7 @@ private:
     CPPUNIT_TEST(testChar32Literal);
     CPPUNIT_TEST(testWcharLiteral);
     CPPUNIT_TEST(testOperations);
+    CPPUNIT_TEST(testOutput);
     CPPUNIT_TEST_SUITE_END();
 
     void testCharLiteral() {
@@ -203,6 +206,12 @@ private:
             v.find_last_not_of("fxo", o3tl::string_view::npos, 2));
         CPPUNIT_ASSERT_EQUAL(npos, v.find_last_not_of("fxo"));
     }
+
+    void testOutput() {
+        std::ostringstream s;
+        s << o3tl::string_view("foo");
+        CPPUNIT_ASSERT_EQUAL(std::string("foo"), s.str());
+    }
 };
 
 CPPUNIT_TEST_SUITE_REGISTRATION(Test);