Improve heuristics for determining whether eager of lazy evaluation is preferred

[rust.git] / clippy_lints / src / methods / unnecessary_lazy_eval.rs

diff --git a/clippy_lints/src/methods/unnecessary_lazy_eval.rs b/clippy_lints/src/methods/unnecessary_lazy_eval.rs
index 08b3eab9b7cdfe3f631b2471c91968a4219184b6..1e2765263c87ddb0ed920c8da8a71b74394ee0b3 100644 (file)
--- a/clippy_lints/src/methods/unnecessary_lazy_eval.rs
+++ b/clippy_lints/src/methods/unnecessary_lazy_eval.rs
@@ -1,24 +1,28 @@
-use crate::utils::{eager_or_lazy, usage};
-use crate::utils::{is_type_diagnostic_item, snippet, span_lint_and_sugg};
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet;
+use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::{eager_or_lazy, usage};
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_lint::LateContext;
+use rustc_span::sym;
 
 use super::UNNECESSARY_LAZY_EVALUATIONS;
 
 /// lint use of `<fn>_else(simple closure)` for `Option`s and `Result`s that can be
 /// replaced with `<fn>(return value of simple closure)`
-pub(super) fn lint<'tcx>(
+pub(super) fn check<'tcx>(
     cx: &LateContext<'tcx>,
     expr: &'tcx hir::Expr<'_>,
-    args: &'tcx [hir::Expr<'_>],
+    recv: &'tcx hir::Expr<'_>,
+    arg: &'tcx hir::Expr<'_>,
     simplify_using: &str,
 ) {
-    let is_option = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&args[0]), sym!(option_type));
-    let is_result = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&args[0]), sym!(result_type));
+    let is_option = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Option);
+    let is_result = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Result);
 
     if is_option || is_result {
-        if let hir::ExprKind::Closure(_, _, eid, _, _) = args[1].kind {
+        if let hir::ExprKind::Closure(_, _, eid, _, _) = arg.kind {
             let body = cx.tcx.hir().body(eid);
             let body_expr = &body.value;
 
@@ -26,26 +30,37 @@ pub(super) fn lint<'tcx>(
                 return;
             }
 
-            if eager_or_lazy::is_eagerness_candidate(cx, body_expr) {
+            if eager_or_lazy::switch_to_eager_eval(cx, body_expr) {
                 let msg = if is_option {
                     "unnecessary closure used to substitute value for `Option::None`"
                 } else {
                     "unnecessary closure used to substitute value for `Result::Err`"
                 };
+                let applicability = if body
+                    .params
+                    .iter()
+                    // bindings are checked to be unused above
+                    .all(|param| matches!(param.pat.kind, hir::PatKind::Binding(..) | hir::PatKind::Wild))
+                {
+                    Applicability::MachineApplicable
+                } else {
+                    // replacing the lambda may break type inference
+                    Applicability::MaybeIncorrect
+                };
 
                 span_lint_and_sugg(
                     cx,
                     UNNECESSARY_LAZY_EVALUATIONS,
                     expr.span,
                     msg,
-                    &format!("Use `{}` instead", simplify_using),
+                    &format!("use `{}` instead", simplify_using),
                     format!(
                         "{0}.{1}({2})",
-                        snippet(cx, args[0].span, ".."),
+                        snippet(cx, recv.span, ".."),
                         simplify_using,
                         snippet(cx, body_expr.span, ".."),
                     ),
-                    Applicability::MachineApplicable,
+                    applicability,
                 );
             }
         }