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+#### Note: this error code is no longer emitted by the compiler.
+
+A `while let` pattern attempts to match the pattern, and enters the body if the
+match was successful. If the match is irrefutable (when it cannot fail to
+match), use a regular `let`-binding inside a `loop` instead. For instance:
+
+```no_run
+struct Irrefutable(i32);
+let irr = Irrefutable(0);
+
+// This fails to compile because the match is irrefutable.
+while let Irrefutable(x) = irr {
+    // ...
+}
+```
+
+Try this instead:
+
+```no_run
+struct Irrefutable(i32);
+let irr = Irrefutable(0);
+
+loop {
+    let Irrefutable(x) = irr;
+    // ...
+}
+```