Auto merge of #7639 - Jarcho:whitelist_cheap_functions, r=camsteffen

Improve heuristic for eagerness suggestion

Still to be done:

* a more complete list of cheap functions
* a way to limit the complexity of cheap expressions

changelog: Improve heuristics for `or_fun_call` and `unnecessary_lazy_evaluations`

Author: bors

clippy_lints/src/functions/too_many_lines.rs

@@ -56,8 +56,8 @@ pub(super) fn check_fn(
                     continue;
                 }
             } else {
-                let multi_idx = line.find("/*").unwrap_or_else(|| line.len());
-                let single_idx = line.find("//").unwrap_or_else(|| line.len());
+                let multi_idx = line.find("/*").unwrap_or(line.len());
+                let single_idx = line.find("//").unwrap_or(line.len());
                 code_in_line |= multi_idx > 0 && single_idx > 0;
                 // Implies multi_idx is below line.len()
                 if multi_idx < single_idx {

clippy_lints/src/methods/from_iter_instead_of_collect.rs

@@ -69,7 +69,7 @@ fn extract_turbofish(cx: &LateContext<'_>, expr: &hir::Expr<'_>, ty: Ty<'tcx>) -
                         // i.e.: 2 wildcards in `std::collections::BTreeMap<&i32, &char>`
                         let ty_str = ty.to_string();
                         let start = ty_str.find('<').unwrap_or(0);
-                        let end = ty_str.find('>').unwrap_or_else(|| ty_str.len());
+                        let end = ty_str.find('>').unwrap_or(ty_str.len());
                         let nb_wildcard = ty_str[start..end].split(',').count();
                         let wildcards = format!("_{}", ", _".repeat(nb_wildcard - 1));
                         format!("{}<{}>", elements.join("::"), wildcards)

clippy_lints/src/methods/or_fun_call.rs

@@ -1,16 +1,12 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::eager_or_lazy::is_lazyness_candidate;
-use clippy_utils::is_trait_item;
+use clippy_utils::eager_or_lazy::switch_to_lazy_eval;
 use clippy_utils::source::{snippet, snippet_with_applicability, snippet_with_macro_callsite};
-use clippy_utils::ty::implements_trait;
-use clippy_utils::ty::{is_type_diagnostic_item, match_type};
-use clippy_utils::{contains_return, last_path_segment, paths};
+use clippy_utils::ty::{implements_trait, match_type};
+use clippy_utils::{contains_return, is_trait_item, last_path_segment, paths};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
-use rustc_hir::{BlockCheckMode, UnsafeSource};
 use rustc_lint::LateContext;
-use rustc_middle::ty;
 use rustc_span::source_map::Span;
 use rustc_span::symbol::{kw, sym};
 use std::borrow::Cow;
@@ -96,25 +92,10 @@ pub(super) fn check<'tcx>(
             (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
         ];
 
-        if let hir::ExprKind::MethodCall(path, _, [self_arg, ..], _) = &arg.kind {
-            if path.ident.name == sym::len {
-                let ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
-
-                match ty.kind() {
-                    ty::Slice(_) | ty::Array(_, _) | ty::Str => return,
-                    _ => (),
-                }
-
-                if is_type_diagnostic_item(cx, ty, sym::Vec) {
-                    return;
-                }
-            }
-        }
-
         if_chain! {
             if KNOW_TYPES.iter().any(|k| k.2.contains(&name));
 
-            if is_lazyness_candidate(cx, arg);
+            if switch_to_lazy_eval(cx, arg);
             if !contains_return(arg);
 
             let self_ty = cx.typeck_results().expr_ty(self_expr);
@@ -166,26 +147,30 @@ pub(super) fn check<'tcx>(
         }
     }
 
-    if args.len() == 2 {
-        match args[1].kind {
+    if let [self_arg, arg] = args {
+        let inner_arg = if let hir::ExprKind::Block(
+            hir::Block {
+                stmts: [],
+                expr: Some(expr),
+                ..
+            },
+            _,
+        ) = arg.kind
+        {
+            expr
+        } else {
+            arg
+        };
+        match inner_arg.kind {
             hir::ExprKind::Call(fun, or_args) => {
                 let or_has_args = !or_args.is_empty();
-                if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
+                if !check_unwrap_or_default(cx, name, fun, self_arg, arg, or_has_args, expr.span) {
                     let fun_span = if or_has_args { None } else { Some(fun.span) };
-                    check_general_case(cx, name, method_span, &args[0], &args[1], expr.span, fun_span);
+                    check_general_case(cx, name, method_span, self_arg, arg, expr.span, fun_span);
                 }
             },
             hir::ExprKind::Index(..) | hir::ExprKind::MethodCall(..) => {
-                check_general_case(cx, name, method_span, &args[0], &args[1], expr.span, None);
-            },
-            hir::ExprKind::Block(block, _)
-                if block.rules == BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided) =>
-            {
-                if let Some(block_expr) = block.expr {
-                    if let hir::ExprKind::MethodCall(..) = block_expr.kind {
-                        check_general_case(cx, name, method_span, &args[0], &args[1], expr.span, None);
-                    }
-                }
+                check_general_case(cx, name, method_span, self_arg, arg, expr.span, None);
             },
             _ => (),
         }

clippy_lints/src/methods/unnecessary_lazy_eval.rs

@@ -30,7 +30,7 @@ pub(super) fn check<'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 {

clippy_lints/src/option_if_let_else.rs

@@ -147,11 +147,7 @@ fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) ->
             let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
             let some_body = extract_body_from_expr(if_then)?;
             let none_body = extract_body_from_expr(if_else)?;
-            let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) {
-                "map_or"
-            } else {
-                "map_or_else"
-            };
+            let method_sugg = if eager_or_lazy::switch_to_eager_eval(cx, none_body) { "map_or" } else { "map_or_else" };
             let capture_name = id.name.to_ident_string();
             let (as_ref, as_mut) = match &let_expr.kind {
                 ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),