Make approx_const MSRV aware

Fixes #7623.

clippy_lints/src/approx_const.rs

@@ -1,8 +1,10 @@
 use clippy_utils::diagnostics::span_lint;
+use clippy_utils::{meets_msrv, msrvs};
 use rustc_ast::ast::{FloatTy, LitFloatType, LitKind};
 use rustc_hir::{Expr, ExprKind};
-use rustc_lint::{LateContext, LateLintPass};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
-use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_semver::RustcVersion;
+use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::symbol;
 use std::f64::consts as f64;
 
@@ -36,68 +38,83 @@ declare_clippy_lint! {
     "the approximate of a known float constant (in `std::fXX::consts`)"
 }
 
-// Tuples are of the form (constant, name, min_digits)
+// Tuples are of the form (constant, name, min_digits, msrv)
-const KNOWN_CONSTS: [(f64, &str, usize); 18] = [
+const KNOWN_CONSTS: [(f64, &str, usize, Option<RustcVersion>); 18] = [
-    (f64::E, "E", 4),
+    (f64::E, "E", 4, None),
-    (f64::FRAC_1_PI, "FRAC_1_PI", 4),
+    (f64::FRAC_1_PI, "FRAC_1_PI", 4, None),
-    (f64::FRAC_1_SQRT_2, "FRAC_1_SQRT_2", 5),
+    (f64::FRAC_1_SQRT_2, "FRAC_1_SQRT_2", 5, None),
-    (f64::FRAC_2_PI, "FRAC_2_PI", 5),
+    (f64::FRAC_2_PI, "FRAC_2_PI", 5, None),
-    (f64::FRAC_2_SQRT_PI, "FRAC_2_SQRT_PI", 5),
+    (f64::FRAC_2_SQRT_PI, "FRAC_2_SQRT_PI", 5, None),
-    (f64::FRAC_PI_2, "FRAC_PI_2", 5),
+    (f64::FRAC_PI_2, "FRAC_PI_2", 5, None),
-    (f64::FRAC_PI_3, "FRAC_PI_3", 5),
+    (f64::FRAC_PI_3, "FRAC_PI_3", 5, None),
-    (f64::FRAC_PI_4, "FRAC_PI_4", 5),
+    (f64::FRAC_PI_4, "FRAC_PI_4", 5, None),
-    (f64::FRAC_PI_6, "FRAC_PI_6", 5),
+    (f64::FRAC_PI_6, "FRAC_PI_6", 5, None),
-    (f64::FRAC_PI_8, "FRAC_PI_8", 5),
+    (f64::FRAC_PI_8, "FRAC_PI_8", 5, None),
-    (f64::LN_2, "LN_2", 5),
+    (f64::LN_2, "LN_2", 5, None),
-    (f64::LN_10, "LN_10", 5),
+    (f64::LN_10, "LN_10", 5, None),
-    (f64::LOG2_10, "LOG2_10", 5),
+    (f64::LOG2_10, "LOG2_10", 5, Some(msrvs::LOG2_10)),
-    (f64::LOG2_E, "LOG2_E", 5),
+    (f64::LOG2_E, "LOG2_E", 5, None),
-    (f64::LOG10_2, "LOG10_2", 5),
+    (f64::LOG10_2, "LOG10_2", 5, Some(msrvs::LOG10_2)),
-    (f64::LOG10_E, "LOG10_E", 5),
+    (f64::LOG10_E, "LOG10_E", 5, None),
-    (f64::PI, "PI", 3),
+    (f64::PI, "PI", 3, None),
-    (f64::SQRT_2, "SQRT_2", 5),
+    (f64::SQRT_2, "SQRT_2", 5, None),
 ];
 
-declare_lint_pass!(ApproxConstant => [APPROX_CONSTANT]);
+pub struct ApproxConstant {
+    msrv: Option<RustcVersion>,
+}
+
+impl ApproxConstant {
+    #[must_use]
+    pub fn new(msrv: Option<RustcVersion>) -> Self {
+        Self { msrv }
+    }
+
+    fn check_lit(&self, cx: &LateContext<'_>, lit: &LitKind, e: &Expr<'_>) {
+        match *lit {
+            LitKind::Float(s, LitFloatType::Suffixed(fty)) => match fty {
+                FloatTy::F32 => self.check_known_consts(cx, e, s, "f32"),
+                FloatTy::F64 => self.check_known_consts(cx, e, s, "f64"),
+            },
+            LitKind::Float(s, LitFloatType::Unsuffixed) => self.check_known_consts(cx, e, s, "f{32, 64}"),
+            _ => (),
+        }
+    }
+
+    fn check_known_consts(&self, cx: &LateContext<'_>, e: &Expr<'_>, s: symbol::Symbol, module: &str) {
+        let s = s.as_str();
+        if s.parse::<f64>().is_ok() {
+            for &(constant, name, min_digits, msrv) in &KNOWN_CONSTS {
+                if is_approx_const(constant, &s, min_digits)
+                    && msrv.as_ref().map_or(true, |msrv| meets_msrv(self.msrv.as_ref(), msrv))
+                {
+                    span_lint(
+                        cx,
+                        APPROX_CONSTANT,
+                        e.span,
+                        &format!(
+                            "approximate value of `{}::consts::{}` found. \
+                             Consider using it directly",
+                            module, &name
+                        ),
+                    );
+                    return;
+                }
+            }
+        }
+    }
+}
+
+impl_lint_pass!(ApproxConstant => [APPROX_CONSTANT]);
 
 impl<'tcx> LateLintPass<'tcx> for ApproxConstant {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
         if let ExprKind::Lit(lit) = &e.kind {
-            check_lit(cx, &lit.node, e);
+            self.check_lit(cx, &lit.node, e);
         }
     }
-}
 
-fn check_lit(cx: &LateContext<'_>, lit: &LitKind, e: &Expr<'_>) {
+    extract_msrv_attr!(LateContext);
-    match *lit {
-        LitKind::Float(s, LitFloatType::Suffixed(fty)) => match fty {
-            FloatTy::F32 => check_known_consts(cx, e, s, "f32"),
-            FloatTy::F64 => check_known_consts(cx, e, s, "f64"),
-        },
-        LitKind::Float(s, LitFloatType::Unsuffixed) => check_known_consts(cx, e, s, "f{32, 64}"),
-        _ => (),
-    }
-}
-
-fn check_known_consts(cx: &LateContext<'_>, e: &Expr<'_>, s: symbol::Symbol, module: &str) {
-    let s = s.as_str();
-    if s.parse::<f64>().is_ok() {
-        for &(constant, name, min_digits) in &KNOWN_CONSTS {
-            if is_approx_const(constant, &s, min_digits) {
-                span_lint(
-                    cx,
-                    APPROX_CONSTANT,
-                    e.span,
-                    &format!(
-                        "approximate value of `{}::consts::{}` found. \
-                         Consider using it directly",
-                        module, &name
-                    ),
-                );
-                return;
-            }
-        }
-    }
 }
 
 /// Returns `false` if the number of significant figures in `value` are

clippy_lints/src/lib.rs

@@ -1865,7 +1865,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| Box::new(needless_bool::NeedlessBool));
     store.register_late_pass(|| Box::new(needless_bool::BoolComparison));
     store.register_late_pass(|| Box::new(needless_for_each::NeedlessForEach));
-    store.register_late_pass(|| Box::new(approx_const::ApproxConstant));
     store.register_late_pass(|| Box::new(misc::MiscLints));
     store.register_late_pass(|| Box::new(eta_reduction::EtaReduction));
     store.register_late_pass(|| Box::new(identity_op::IdentityOp));
@@ -1894,6 +1893,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     });
 
     let avoid_breaking_exported_api = conf.avoid_breaking_exported_api;
+    store.register_late_pass(move || Box::new(approx_const::ApproxConstant::new(msrv)));
     store.register_late_pass(move || Box::new(methods::Methods::new(avoid_breaking_exported_api, msrv)));
     store.register_late_pass(move || Box::new(matches::Matches::new(msrv)));
     store.register_early_pass(move || Box::new(manual_non_exhaustive::ManualNonExhaustive::new(msrv)));

clippy_utils/src/msrvs.rs

@@ -17,6 +17,7 @@ msrv_aliases! {
     1,50,0 { BOOL_THEN }
     1,46,0 { CONST_IF_MATCH }
     1,45,0 { STR_STRIP_PREFIX }
+    1,43,0 { LOG2_10, LOG10_2 }
     1,42,0 { MATCHES_MACRO }
     1,41,0 { RE_REBALANCING_COHERENCE, RESULT_MAP_OR_ELSE }
     1,40,0 { MEM_TAKE, NON_EXHAUSTIVE, OPTION_AS_DEREF }

tests/ui/min_rust_version_attr.rs

@@ -4,6 +4,11 @@
 
 use std::ops::{Deref, RangeFrom};
 
+fn approx_const() {
+    let log2_10 = 3.321928094887362;
+    let log10_2 = 0.301029995663981;
+}
+
 fn cloned_instead_of_copied() {
     let _ = [1].iter().cloned();
 }

tests/ui/min_rust_version_attr.stderr

@@ -1,12 +1,12 @@
 error: stripping a prefix manually
-  --> $DIR/min_rust_version_attr.rs:160:24
+  --> $DIR/min_rust_version_attr.rs:165:24
    |
 LL |             assert_eq!(s["hello, ".len()..].to_uppercase(), "WORLD!");
    |                        ^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::manual-strip` implied by `-D warnings`
 note: the prefix was tested here
-  --> $DIR/min_rust_version_attr.rs:159:9
+  --> $DIR/min_rust_version_attr.rs:164:9
    |
 LL |         if s.starts_with("hello, ") {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -17,13 +17,13 @@ LL ~             assert_eq!(<stripped>.to_uppercase(), "WORLD!");
    |
 
 error: stripping a prefix manually
-  --> $DIR/min_rust_version_attr.rs:172:24
+  --> $DIR/min_rust_version_attr.rs:177:24
    |
 LL |             assert_eq!(s["hello, ".len()..].to_uppercase(), "WORLD!");
    |                        ^^^^^^^^^^^^^^^^^^^^
    |
 note: the prefix was tested here
-  --> $DIR/min_rust_version_attr.rs:171:9
+  --> $DIR/min_rust_version_attr.rs:176:9
    |
 LL |         if s.starts_with("hello, ") {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^