Check for comparisons to NaN in patterns

For every pattern that refers to a static value, evaluate it and emit a warning
if it is a NaN.

Fixes #6804

1 files changed, 16 insertions, 0 deletions

diff --git a/src/test/compile-fail/issue-6804.rs b/src/test/compile-fail/issue-6804.rs
new file mode 100644
index 00000000000..85e09a777d1
--- /dev/null
+++ b/src/test/compile-fail/issue-6804.rs
@@ -0,0 +1,16 @@
+// Matching against NaN should result in a warning
+
+use std::float::NaN;
+
+fn main() {
+    let x = NaN;
+    match x {
+        NaN => {},
+        _ => {},
+    };
+    //~^^^ WARNING unmatchable NaN in pattern, use is_NaN() in a guard instead
+}
+
+// At least one error is needed so that compilation fails
+#[static_assert]
+static b: bool = false; //~ ERROR static assertion failed