restrict manual_clamp to const case, bring it out of nursery

clippy_lints/src/manual_clamp.rs

@@ -1,4 +1,5 @@
 use clippy_config::msrvs::{self, Msrv};
+use clippy_utils::consts::{constant, Constant};
 use clippy_utils::diagnostics::{span_lint_and_then, span_lint_hir_and_then};
 use clippy_utils::higher::If;
 use clippy_utils::sugg::Sugg;
@@ -17,6 +18,7 @@ use rustc_middle::ty::Ty;
 use rustc_session::impl_lint_pass;
 use rustc_span::symbol::sym;
 use rustc_span::Span;
+use std::cmp::Ordering;
 use std::ops::Deref;
 
 declare_clippy_lint! {
@@ -26,6 +28,11 @@ declare_clippy_lint! {
     /// ### Why is this bad?
     /// clamp is much shorter, easier to read, and doesn't use any control flow.
     ///
+    /// ### Limitations
+    ///
+    /// This lint will only trigger if max and min are known at compile time, and max is
+    /// greater than min.
+    ///
     /// ### Known issue(s)
     /// If the clamped variable is NaN this suggestion will cause the code to propagate NaN
     /// rather than returning either `max` or `min`.
@@ -80,7 +87,7 @@ declare_clippy_lint! {
     /// ```
     #[clippy::version = "1.66.0"]
     pub MANUAL_CLAMP,
-    nursery,
+    complexity,
     "using a clamp pattern instead of the clamp function"
 }
 impl_lint_pass!(ManualClamp => [MANUAL_CLAMP]);
@@ -103,6 +110,26 @@ struct ClampSuggestion<'tcx> {
     hir_with_ignore_attr: Option<HirId>,
 }
 
+impl<'tcx> ClampSuggestion<'tcx> {
+    /// This function will return true if and only if you can demonstrate at compile time that min
+    /// is less than max.
+    fn min_less_than_max(&self, cx: &LateContext<'tcx>) -> bool {
+        let max_type = cx.typeck_results().expr_ty(self.params.max);
+        let min_type = cx.typeck_results().expr_ty(self.params.min);
+        if max_type != min_type {
+            return false;
+        }
+        if let Some(max) = constant(cx, cx.typeck_results(), self.params.max)
+            && let Some(min) = constant(cx, cx.typeck_results(), self.params.min)
+            && let Some(ord) = Constant::partial_cmp(cx.tcx, max_type, &min, &max)
+        {
+            ord != Ordering::Greater
+        } else {
+            false
+        }
+    }
+}
+
 #[derive(Debug)]
 struct InputMinMax<'tcx> {
     input: &'tcx Expr<'tcx>,
@@ -123,7 +150,7 @@ impl<'tcx> LateLintPass<'tcx> for ManualClamp {
                 .or_else(|| is_match_pattern(cx, expr))
                 .or_else(|| is_if_elseif_pattern(cx, expr));
             if let Some(suggestion) = suggestion {
-                emit_suggestion(cx, &suggestion);
+                maybe_emit_suggestion(cx, &suggestion);
             }
         }
     }
@@ -133,13 +160,16 @@ impl<'tcx> LateLintPass<'tcx> for ManualClamp {
             return;
         }
         for suggestion in is_two_if_pattern(cx, block) {
-            emit_suggestion(cx, &suggestion);
+            maybe_emit_suggestion(cx, &suggestion);
         }
     }
     extract_msrv_attr!(LateContext);
 }
 
-fn emit_suggestion<'tcx>(cx: &LateContext<'tcx>, suggestion: &ClampSuggestion<'tcx>) {
+fn maybe_emit_suggestion<'tcx>(cx: &LateContext<'tcx>, suggestion: &ClampSuggestion<'tcx>) {
+    if !suggestion.min_less_than_max(cx) {
+        return;
+    }
     let ClampSuggestion {
         params: InputMinMax {
             input,