Treating the unused equality comparisons as something other than part of

-Wunused was a mistake. It resulted in duplicate warnings and lots of
other hacks. Instead, this should be a special sub-category to
-Wunused-value, much like -Wunused-result is.

Moved to -Wunused-comparison, moved the implementation to piggy back on
the -Wunused-value implementation instead of rolling its own, different
mechanism for catching all of the "interesting" statements.

I like the unused-value mechanism for this better, but its currently
missing several top-level statements. For now, I've FIXME-ed out those
test cases. I'll enhance the generic infrastructure to catch these
statements in a subsequent patch.

This patch also removes the cast-to-void fixit hint. This hint isn't
available on any of the other -Wunused-value diagnostics, and if we want
it to be, we should add it generically rather than in one specific case.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@137822 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 72 insertions, 0 deletions

diff --git a/test/SemaCXX/warn-unused-comparison.cpp b/test/SemaCXX/warn-unused-comparison.cpp
new file mode 100644
index 0000000000..79a644cefc
--- /dev/null
+++ b/test/SemaCXX/warn-unused-comparison.cpp
@@ -0,0 +1,72 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wno-unused -Wunused-comparison %s
+
+struct A {
+  bool operator==(const A&);
+  bool operator!=(const A&);
+  A operator|=(const A&);
+  operator bool();
+};
+
+void test() {
+  int x, *p;
+  A a, b;
+
+  x == 7; // expected-warning {{equality comparison result unused}} \
+          // expected-note {{use '=' to turn this equality comparison into an assignment}}
+  x != 7; // expected-warning {{inequality comparison result unused}} \
+          // expected-note {{use '|=' to turn this inequality comparison into an or-assignment}}
+  7 == x; // expected-warning {{equality comparison result unused}}
+  p == p; // expected-warning {{equality comparison result unused}} \
+          // expected-note {{use '=' to turn this equality comparison into an assignment}} \
+          // expected-warning {{self-comparison always evaluates to true}}
+  a == a; // FIXME: missing-warning {{equality comparison result unused}} \
+          // FIXME: missing-note {{use '=' to turn this equality comparison into an assignment}}
+  a == b; // FIXME: missing-warning {{equality comparison result unused}} \
+          // FIXME: missing-note {{use '=' to turn this equality comparison into an assignment}}
+  a != b; // FIXME: missing-warning {{inequality comparison result unused}} \
+          // FIXME: missing-note {{use '|=' to turn this inequality comparison into an or-assignment}}
+  A() == b; // FIXME: missing-warning {{equality comparison result unused}}
+  if (42) x == 7; // expected-warning {{equality comparison result unused}} \
+                  // expected-note {{use '=' to turn this equality comparison into an assignment}}
+  else if (42) x == 7; // expected-warning {{equality comparison result unused}} \
+                       // expected-note {{use '=' to turn this equality comparison into an assignment}}
+  else x == 7; // expected-warning {{equality comparison result unused}} \
+               // expected-note {{use '=' to turn this equality comparison into an assignment}}
+  do x == 7; // expected-warning {{equality comparison result unused}} \
+             // expected-note {{use '=' to turn this equality comparison into an assignment}}
+  while (false);
+  while (false) x == 7; // expected-warning {{equality comparison result unused}} \
+                        // expected-note {{use '=' to turn this equality comparison into an assignment}}
+  for (x == 7; // expected-warning {{equality comparison result unused}} \
+               // expected-note {{use '=' to turn this equality comparison into an assignment}}
+       x == 7; // No warning -- result is used
+       x == 7) // expected-warning {{equality comparison result unused}} \
+               // expected-note {{use '=' to turn this equality comparison into an assignment}}
+    x == 7; // expected-warning {{equality comparison result unused}} \
+            // expected-note {{use '=' to turn this equality comparison into an assignment}}
+  switch (42) default: x == 7; // FIXME: missing-warning {{equality comparison result unused}} \
+                               // FIXME: missing-note {{use '=' to turn this equality comparison into an assignment}}
+  switch (42) case 42: x == 7; // FIXME: missing-warning {{equality comparison result unused}} \
+                               // FIXME: missing-note {{use '=' to turn this equality comparison into an assignment}}
+  switch (42) {
+    case 1:
+    case 2:
+    default:
+    case 3:
+    case 4:
+      x == 7; // FIXME: missing-warning {{equality comparison result unused}} \
+              // FIXME: missing-note {{use '=' to turn this equality comparison into an assignment}}
+  }
+
+  (void)(x == 7);
+  (void)(p == p); // expected-warning {{self-comparison always evaluates to true}}
+  { bool b = x == 7; }
+
+  { bool b = ({ x == 7; // expected-warning {{equality comparison result unused}} \
+                        // expected-note {{use '=' to turn this equality comparison into an assignment}}
+                x == 7; }); } // no warning on the second, its result is used!
+
+#define EQ(x,y) (x) == (y)
+  EQ(x, 5);
+#undef EQ
+}