Lint logbase for arbitrary base

Author: thiagoarrais

clippy_lints/src/floating_point_arithmetic.rs

@@ -573,12 +573,17 @@ fn check_custom_abs(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
     }
 }
 
-fn are_same_base_logs(expr_a: &Expr<'_>, expr_b: &Expr<'_>) -> bool {
+fn are_same_base_logs(cx: &LateContext<'_, '_>, expr_a: &Expr<'_>, expr_b: &Expr<'_>) -> bool {
     if_chain! {
-        if let ExprKind::MethodCall(PathSegment { ident: method_name_a, .. }, _, _) = expr_a.kind;
-        if let ExprKind::MethodCall(PathSegment { ident: method_name_b, .. }, _, _) = expr_b.kind;
+        if let ExprKind::MethodCall(PathSegment { ident: method_name_a, .. }, _, ref args_a) = expr_a.kind;
+        if let ExprKind::MethodCall(PathSegment { ident: method_name_b, .. }, _, ref args_b) = expr_b.kind;
         then {
-            return method_name_a.as_str() == method_name_b.as_str() && ["ln", "log2", "log10"].contains(&&*method_name_a.as_str());
+            return method_name_a.as_str() == method_name_b.as_str() &&
+                args_a.len() == args_b.len() &&
+                (
+                    ["ln", "log2", "log10"].contains(&&*method_name_a.as_str()) ||
+                    method_name_a.as_str() == "log" && args_a.len() == 2 && are_exprs_equal(cx, &args_a[1], &args_b[1])
+                );
         }
     }
 
@@ -595,7 +600,7 @@ fn check_logbase(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
             lhs,
             rhs,
         ) = &expr.kind;
-        if are_same_base_logs(lhs, rhs);
+        if are_same_base_logs(cx, lhs, rhs);
         if let ExprKind::MethodCall(_, _, ref largs) = lhs.kind;
         if let ExprKind::MethodCall(_, _, ref rargs) = rhs.kind;
         then {

tests/ui/floating_point_logbase.fixed

@@ -7,8 +7,10 @@ fn main() {
     let _ = x.log(y);
     let _ = x.log(y);
     let _ = x.log(y);
+    let _ = x.log(y);
     // Cases where the lint shouldn't be applied
     let _ = x.ln() / y.powf(3.2);
     let _ = x.powf(3.2) / y.powf(3.2);
     let _ = x.powf(3.2) / y.ln();
+    let _ = x.log(5f32) / y.log(7f32);
 }

tests/ui/floating_point_logbase.rs

@@ -7,8 +7,10 @@ fn main() {
     let _ = x.ln() / y.ln();
     let _ = x.log2() / y.log2();
     let _ = x.log10() / y.log10();
+    let _ = x.log(5f32) / y.log(5f32);
     // Cases where the lint shouldn't be applied
     let _ = x.ln() / y.powf(3.2);
     let _ = x.powf(3.2) / y.powf(3.2);
     let _ = x.powf(3.2) / y.ln();
+    let _ = x.log(5f32) / y.log(7f32);
 }

tests/ui/floating_point_logbase.stderr

@@ -18,5 +18,11 @@ error: division of logarithms can be calculated more efficiently and accurately
 LL |     let _ = x.log10() / y.log10();
    |             ^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`
 
-error: aborting due to 3 previous errors
+error: division of logarithms can be calculated more efficiently and accurately
+  --> $DIR/floating_point_logbase.rs:10:13
+   |
+LL |     let _ = x.log(5f32) / y.log(5f32);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.log(y)`
+
+error: aborting due to 4 previous errors