[libcxx] [test] Change ifstream constructor tests to handle read-only files.

[STL_MSFT]

Summary

[libcxx] [test] Change ifstream constructor tests to handle read-only files.

Certain source control systems like to set the read-only bit on their files,
which interferes with opening "test.dat" for both input and output.
Fortunately, we can work around this without losing test coverage.
Now, the ifstream.cons tests have comments referring to the ofstream.cons tests.
There, we're creating writable files (not checked into source control),
where the ifstream constructor tests will succeed.

[EricWF]

I really dislike this change. I'm afraid that these changes allow the tests to silently fail for reasons other than test.dat being read only. For example if test.dat ever gets deleted, or if libc++'s remote test-harness fails to copy the input file to the remote host.

I'm not sure how to work around your read-only VCS issue though... Do you have any other ideas?

[STL_MSFT]

My changes to the ofstream.cons tests preserve the test coverage (as they already contain the machinery to create writable files).

Would you like it if I removed the "if (fs) { stuff }" blocks from the ifstream.cons tests entirely, and changed the comments to say things along the lines of "for basic_ifstream(const char *, ios_base::openmode) tests, we need writable files, so see BLAH"?

[STL_MSFT]

Instead of skipping failures to open, just have comments pointing to the ofstream.cons tests where this coverage has moved.

[STL_MSFT]

As yet another alternative, I could keep the ios_base::openmode tests in ifstream.cons, but use ios_base::binary instead of ios_base::out.

[EricWF]

LGTM. Thanks for working on this.

test/std/input.output/file.streams/fstreams/ifstream.cons/pointer.pass.cpp

 int main()
 {
     {
         std::ifstream fs("test.dat");
         double x = 0;
         fs >> x;
         assert(x == 3.25);
     }
-    {
-        std::ifstream fs("test.dat", std::ios_base::out);
-        double x = 0;
-        fs >> x;
-        assert(x == 3.25);
-    }
+    // std::ifstream(const char*, std::ios_base::openmode) is tested in
+    // test/std/input.output/file.streams/fstreams/ofstream.cons/pointer.pass.cpp
+    // which creates writable files.
     {
         std::wifstream fs("test.dat");
         double x = 0;
         fs >> x;
         assert(x == 3.25);
     }
-    {
-        std::wifstream fs("test.dat", std::ios_base::out);
-        double x = 0;
-        fs >> x;
-        assert(x == 3.25);
-    }
+    // std::wifstream(const char*, std::ios_base::openmode) is tested in
+    // test/std/input.output/file.streams/fstreams/ofstream.cons/pointer.pass.cpp
+    // which creates writable files.
 }

test/std/input.output/file.streams/fstreams/ifstream.cons/string.pass.cpp

 int main()
 {
     {
         std::ifstream fs(std::string("test.dat"));
         double x = 0;
         fs >> x;
         assert(x == 3.25);
     }
-    {
-        std::ifstream fs(std::string("test.dat"), std::ios_base::out);
-        double x = 0;
-        fs >> x;
-        assert(x == 3.25);
-    }
+    // std::ifstream(const std::string&, std::ios_base::openmode) is tested in
+    // test/std/input.output/file.streams/fstreams/ofstream.cons/string.pass.cpp
+    // which creates writable files.
     {
         std::wifstream fs(std::string("test.dat"));
         double x = 0;
         fs >> x;
         assert(x == 3.25);
     }
-    {
-        std::wifstream fs(std::string("test.dat"), std::ios_base::out);
-        double x = 0;
-        fs >> x;
-        assert(x == 3.25);
-    }
+    // std::wifstream(const std::string&, std::ios_base::openmode) is tested in
+    // test/std/input.output/file.streams/fstreams/ofstream.cons/string.pass.cpp
+    // which creates writable files.
 }

test/std/input.output/file.streams/fstreams/ofstream.cons/pointer.pass.cpp

std::string temp = get_temp_file_name();
         fs << 3.25;
     }
     {
         std::ifstream fs(temp.c_str());
         double x = 0;
         fs >> x;
         assert(x == 3.25);
     }
+    {
+        std::ifstream fs(temp.c_str(), std::ios_base::out);
+        double x = 0;
+        fs >> x;
+        assert(x == 3.25);
+    }
     std::remove(temp.c_str());
     {
         std::wofstream fs(temp.c_str());
         fs << 3.25;
     }
     {
         std::wifstream fs(temp.c_str());
         double x = 0;
         fs >> x;
         assert(x == 3.25);
     }
+    {
+        std::wifstream fs(temp.c_str(), std::ios_base::out);
+        double x = 0;
+        fs >> x;
+        assert(x == 3.25);
+    }
     std::remove(temp.c_str());
 }

test/std/input.output/file.streams/fstreams/ofstream.cons/string.pass.cpp

std::string temp = get_temp_file_name();
         fs << 3.25;
     }
     {
         std::ifstream fs(temp);
         double x = 0;
         fs >> x;
         assert(x == 3.25);
     }
+    {
+        std::ifstream fs(temp, std::ios_base::out);
+        double x = 0;
+        fs >> x;
+        assert(x == 3.25);
+    }
     std::remove(temp.c_str());
     {
         std::wofstream fs(temp);
         fs << 3.25;
     }
     {
         std::wifstream fs(temp);
         double x = 0;
         fs >> x;
         assert(x == 3.25);
     }
+    {
+        std::wifstream fs(temp, std::ios_base::out);
+        double x = 0;
+        fs >> x;
+        assert(x == 3.25);
+    }
     std::remove(temp.c_str());
 }