Auto merge of rust-lang#5937 - montrivo:option_if_let_else, r=flip1995

option_if_let_else - distinguish pure from impure else expressions

Addresses partially rust-lang#5821.

changelog: improve the lint `option_if_let_else`. Suggest `map_or` or `map_or_else` based on the else expression purity.

clippy_lints/src/methods/bind_instead_of_map.rs

@@ -12,6 +12,7 @@ use rustc_middle::hir::map::Map;
 use rustc_span::Span;
 
 pub(crate) struct OptionAndThenSome;
+
 impl BindInsteadOfMap for OptionAndThenSome {
     const TYPE_NAME: &'static str = "Option";
     const TYPE_QPATH: &'static [&'static str] = &paths::OPTION;
@@ -24,6 +25,7 @@ impl BindInsteadOfMap for OptionAndThenSome {
 }
 
 pub(crate) struct ResultAndThenOk;
+
 impl BindInsteadOfMap for ResultAndThenOk {
     const TYPE_NAME: &'static str = "Result";
     const TYPE_QPATH: &'static [&'static str] = &paths::RESULT;
@@ -36,6 +38,7 @@ impl BindInsteadOfMap for ResultAndThenOk {
 }
 
 pub(crate) struct ResultOrElseErrInfo;
+
 impl BindInsteadOfMap for ResultOrElseErrInfo {
     const TYPE_NAME: &'static str = "Result";
     const TYPE_QPATH: &'static [&'static str] = &paths::RESULT;
@@ -120,9 +123,9 @@ pub(crate) trait BindInsteadOfMap {
         }
     }
 
-    fn lint_closure(cx: &LateContext<'_>, expr: &hir::Expr<'_>, closure_expr: &hir::Expr<'_>) {
+    fn lint_closure(cx: &LateContext<'_>, expr: &hir::Expr<'_>, closure_expr: &hir::Expr<'_>) -> bool {
         let mut suggs = Vec::new();
-        let can_sugg = find_all_ret_expressions(cx, closure_expr, |ret_expr| {
+        let can_sugg: bool = find_all_ret_expressions(cx, closure_expr, |ret_expr| {
             if_chain! {
                 if !in_macro(ret_expr.span);
                 if let hir::ExprKind::Call(ref func_path, ref args) = ret_expr.kind;
@@ -153,21 +156,24 @@ pub(crate) trait BindInsteadOfMap {
                 )
             });
         }
+        can_sugg
     }
 
     /// Lint use of `_.and_then(|x| Some(y))` for `Option`s
-    fn lint(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
+    fn lint(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) -> bool {
         if !match_type(cx, cx.typeck_results().expr_ty(&args[0]), Self::TYPE_QPATH) {
-            return;
+            return false;
         }
 
         match args[1].kind {
             hir::ExprKind::Closure(_, _, body_id, closure_args_span, _) => {
                 let closure_body = cx.tcx.hir().body(body_id);
                 let closure_expr = remove_blocks(&closure_body.value);
 
-                if !Self::lint_closure_autofixable(cx, expr, args, closure_expr, closure_args_span) {
-                    Self::lint_closure(cx, expr, closure_expr);
+                if Self::lint_closure_autofixable(cx, expr, args, closure_expr, closure_args_span) {
+                    true
+                } else {
+                    Self::lint_closure(cx, expr, closure_expr)
                 }
             },
             // `_.and_then(Some)` case, which is no-op.
@@ -181,8 +187,9 @@ pub(crate) trait BindInsteadOfMap {
                     snippet(cx, args[0].span, "..").into(),
                     Applicability::MachineApplicable,
                 );
+                true
             },
-            _ => {},
+            _ => false,
         }
     }
 }

clippy_lints/src/methods/mod.rs

@@ -25,14 +25,15 @@ use rustc_span::source_map::Span;
 use rustc_span::symbol::{sym, SymbolStr};
 
 use crate::consts::{constant, Constant};
+use crate::utils::eager_or_lazy::is_lazyness_candidate;
 use crate::utils::usage::mutated_variables;
 use crate::utils::{
     contains_ty, get_arg_name, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait, in_macro,
-    is_copy, is_ctor_or_promotable_const_function, is_expn_of, is_type_diagnostic_item, iter_input_pats,
-    last_path_segment, match_def_path, match_qpath, match_trait_method, match_type, match_var, method_calls,
-    method_chain_args, paths, remove_blocks, return_ty, single_segment_path, snippet, snippet_with_applicability,
-    snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_note, span_lint_and_sugg,
-    span_lint_and_then, sugg, walk_ptrs_ty, walk_ptrs_ty_depth, SpanlessEq,
+    is_copy, is_expn_of, is_type_diagnostic_item, iter_input_pats, last_path_segment, match_def_path, match_qpath,
+    match_trait_method, match_type, match_var, method_calls, method_chain_args, paths, remove_blocks, return_ty,
+    single_segment_path, snippet, snippet_with_applicability, snippet_with_macro_callsite, span_lint,
+    span_lint_and_help, span_lint_and_note, span_lint_and_sugg, span_lint_and_then, sugg, walk_ptrs_ty,
+    walk_ptrs_ty_depth, SpanlessEq,
 };
 
 declare_clippy_lint! {
@@ -1454,18 +1455,21 @@ impl<'tcx> LateLintPass<'tcx> for Methods {
             ["unwrap_or", "map"] => option_map_unwrap_or::lint(cx, expr, arg_lists[1], arg_lists[0], method_spans[1]),
             ["unwrap_or_else", "map"] => {
                 if !lint_map_unwrap_or_else(cx, expr, arg_lists[1], arg_lists[0]) {
-                    unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], true, "unwrap_or");
+                    unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "unwrap_or");
                 }
             },
             ["map_or", ..] => lint_map_or_none(cx, expr, arg_lists[0]),
             ["and_then", ..] => {
-                unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], false, "and");
-                bind_instead_of_map::OptionAndThenSome::lint(cx, expr, arg_lists[0]);
-                bind_instead_of_map::ResultAndThenOk::lint(cx, expr, arg_lists[0]);
+                let biom_option_linted = bind_instead_of_map::OptionAndThenSome::lint(cx, expr, arg_lists[0]);
+                let biom_result_linted = bind_instead_of_map::ResultAndThenOk::lint(cx, expr, arg_lists[0]);
+                if !biom_option_linted && !biom_result_linted {
+                    unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "and");
+                }
             },
             ["or_else", ..] => {
-                unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], false, "or");
-                bind_instead_of_map::ResultOrElseErrInfo::lint(cx, expr, arg_lists[0]);
+                if !bind_instead_of_map::ResultOrElseErrInfo::lint(cx, expr, arg_lists[0]) {
+                    unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "or");
+                }
             },
             ["next", "filter"] => lint_filter_next(cx, expr, arg_lists[1]),
             ["next", "skip_while"] => lint_skip_while_next(cx, expr, arg_lists[1]),
@@ -1508,9 +1512,9 @@ impl<'tcx> LateLintPass<'tcx> for Methods {
             ["is_file", ..] => lint_filetype_is_file(cx, expr, arg_lists[0]),
             ["map", "as_ref"] => lint_option_as_ref_deref(cx, expr, arg_lists[1], arg_lists[0], false),
             ["map", "as_mut"] => lint_option_as_ref_deref(cx, expr, arg_lists[1], arg_lists[0], true),
-            ["unwrap_or_else", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], true, "unwrap_or"),
-            ["get_or_insert_with", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], true, "get_or_insert"),
-            ["ok_or_else", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], true, "ok_or"),
+            ["unwrap_or_else", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "unwrap_or"),
+            ["get_or_insert_with", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "get_or_insert"),
+            ["ok_or_else", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "ok_or"),
             _ => {},
         }
 
@@ -1714,37 +1718,6 @@ fn lint_or_fun_call<'tcx>(
     name: &str,
     args: &'tcx [hir::Expr<'_>],
 ) {
-    // Searches an expression for method calls or function calls that aren't ctors
-    struct FunCallFinder<'a, 'tcx> {
-        cx: &'a LateContext<'tcx>,
-        found: bool,
-    }
-
-    impl<'a, 'tcx> intravisit::Visitor<'tcx> for FunCallFinder<'a, 'tcx> {
-        type Map = Map<'tcx>;
-
-        fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
-            let call_found = match &expr.kind {
-                // ignore enum and struct constructors
-                hir::ExprKind::Call(..) => !is_ctor_or_promotable_const_function(self.cx, expr),
-                hir::ExprKind::MethodCall(..) => true,
-                _ => false,
-            };
-
-            if call_found {
-                self.found |= true;
-            }
-
-            if !self.found {
-                intravisit::walk_expr(self, expr);
-            }
-        }
-
-        fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
-            intravisit::NestedVisitorMap::None
-        }
-    }
-
     /// Checks for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
     fn check_unwrap_or_default(
         cx: &LateContext<'_>,
@@ -1825,8 +1798,7 @@ fn lint_or_fun_call<'tcx>(
         if_chain! {
             if know_types.iter().any(|k| k.2.contains(&name));
 
-            let mut finder = FunCallFinder { cx: &cx, found: false };
-            if { finder.visit_expr(&arg); finder.found };
+            if is_lazyness_candidate(cx, arg);
             if !contains_return(&arg);
 
             let self_ty = cx.typeck_results().expr_ty(self_expr);

clippy_lints/src/methods/unnecessary_lazy_eval.rs

@@ -1,78 +1,17 @@
-use crate::utils::{is_type_diagnostic_item, match_qpath, snippet, span_lint_and_sugg};
-use if_chain::if_chain;
+use crate::utils::{eager_or_lazy, usage};
+use crate::utils::{is_type_diagnostic_item, snippet, span_lint_and_sugg};
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_lint::LateContext;
 
 use super::UNNECESSARY_LAZY_EVALUATIONS;
 
-// Return true if the expression is an accessor of any of the arguments
-fn expr_uses_argument(expr: &hir::Expr<'_>, params: &[hir::Param<'_>]) -> bool {
-    params.iter().any(|arg| {
-        if_chain! {
-            if let hir::PatKind::Binding(_, _, ident, _) = arg.pat.kind;
-            if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.kind;
-            if let [p, ..] = path.segments;
-            then {
-                ident.name == p.ident.name
-            } else {
-                false
-            }
-        }
-    })
-}
-
-fn match_any_qpath(path: &hir::QPath<'_>, paths: &[&[&str]]) -> bool {
-    paths.iter().any(|candidate| match_qpath(path, candidate))
-}
-
-fn can_simplify(expr: &hir::Expr<'_>, params: &[hir::Param<'_>], variant_calls: bool) -> bool {
-    match expr.kind {
-        // Closures returning literals can be unconditionally simplified
-        hir::ExprKind::Lit(_) => true,
-
-        hir::ExprKind::Index(ref object, ref index) => {
-            // arguments are not being indexed into
-            if expr_uses_argument(object, params) {
-                false
-            } else {
-                // arguments are not used as index
-                !expr_uses_argument(index, params)
-            }
-        },
-
-        // Reading fields can be simplified if the object is not an argument of the closure
-        hir::ExprKind::Field(ref object, _) => !expr_uses_argument(object, params),
-
-        // Paths can be simplified if the root is not the argument, this also covers None
-        hir::ExprKind::Path(_) => !expr_uses_argument(expr, params),
-
-        // Calls to Some, Ok, Err can be considered literals if they don't derive an argument
-        hir::ExprKind::Call(ref func, ref args) => if_chain! {
-            if variant_calls; // Disable lint when rules conflict with bind_instead_of_map
-            if let hir::ExprKind::Path(ref path) = func.kind;
-            if match_any_qpath(path, &[&["Some"], &["Ok"], &["Err"]]);
-            then {
-                // Recursively check all arguments
-                args.iter().all(|arg| can_simplify(arg, params, variant_calls))
-            } else {
-                false
-            }
-        },
-
-        // For anything more complex than the above, a closure is probably the right solution,
-        // or the case is handled by an other lint
-        _ => false,
-    }
-}
-
 /// 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>(
     cx: &LateContext<'tcx>,
     expr: &'tcx hir::Expr<'_>,
     args: &'tcx [hir::Expr<'_>],
-    allow_variant_calls: bool,
     simplify_using: &str,
 ) {
     let is_option = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&args[0]), sym!(option_type));
@@ -81,10 +20,13 @@ pub(super) fn lint<'tcx>(
     if is_option || is_result {
         if let hir::ExprKind::Closure(_, _, eid, _, _) = args[1].kind {
             let body = cx.tcx.hir().body(eid);
-            let ex = &body.value;
-            let params = &body.params;
+            let body_expr = &body.value;
+
+            if usage::BindingUsageFinder::are_params_used(cx, body) {
+                return;
+            }
 
-            if can_simplify(ex, params, allow_variant_calls) {
+            if eager_or_lazy::is_eagerness_candidate(cx, body_expr) {
                 let msg = if is_option {
                     "unnecessary closure used to substitute value for `Option::None`"
                 } else {
@@ -101,7 +43,7 @@ pub(super) fn lint<'tcx>(
                         "{0}.{1}({2})",
                         snippet(cx, args[0].span, ".."),
                         simplify_using,
-                        snippet(cx, ex.span, ".."),
+                        snippet(cx, body_expr.span, ".."),
                     ),
                     Applicability::MachineApplicable,
                 );

clippy_lints/src/option_if_let_else.rs

@@ -1,4 +1,5 @@
 use crate::utils;
+use crate::utils::eager_or_lazy;
 use crate::utils::sugg::Sugg;
 use crate::utils::{is_type_diagnostic_item, paths, span_lint_and_sugg};
 use if_chain::if_chain;
@@ -13,22 +14,16 @@ use rustc_session::{declare_lint_pass, declare_tool_lint};
 declare_clippy_lint! {
     /// **What it does:**
     /// Lints usage of  `if let Some(v) = ... { y } else { x }` which is more
-    /// idiomatically done with `Option::map_or` (if the else bit is a simple
-    /// expression) or `Option::map_or_else` (if the else bit is a longer
-    /// block).
+    /// idiomatically done with `Option::map_or` (if the else bit is a pure
+    /// expression) or `Option::map_or_else` (if the else bit is an impure
+    /// expresion).
     ///
     /// **Why is this bad?**
     /// Using the dedicated functions of the Option type is clearer and
     /// more concise than an if let expression.
     ///
     /// **Known problems:**
-    /// This lint uses whether the block is just an expression or if it has
-    /// more statements to decide whether to use `Option::map_or` or
-    /// `Option::map_or_else`. If you have a single expression which calls
-    /// an expensive function, then it would be more efficient to use
-    /// `Option::map_or_else`, but this lint would suggest `Option::map_or`.
-    ///
-    /// Also, this lint uses a deliberately conservative metric for checking
+    /// This lint uses a deliberately conservative metric for checking
     /// if the inside of either body contains breaks or continues which will
     /// cause it to not suggest a fix if either block contains a loop with
     /// continues or breaks contained within the loop.
@@ -92,13 +87,15 @@ struct OptionIfLetElseOccurence {
 struct ReturnBreakContinueMacroVisitor {
     seen_return_break_continue: bool,
 }
+
 impl ReturnBreakContinueMacroVisitor {
     fn new() -> ReturnBreakContinueMacroVisitor {
         ReturnBreakContinueMacroVisitor {
             seen_return_break_continue: false,
         }
     }
 }
+
 impl<'tcx> Visitor<'tcx> for ReturnBreakContinueMacroVisitor {
     type Map = Map<'tcx>;
     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
@@ -157,7 +154,7 @@ fn extract_body_from_arm<'a>(arm: &'a Arm<'a>) -> Option<&'a Expr<'a>> {
 }
 
 /// If this is the else body of an if/else expression, then we need to wrap
-/// it in curcly braces. Otherwise, we don't.
+/// it in curly braces. Otherwise, we don't.
 fn should_wrap_in_braces(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     utils::get_enclosing_block(cx, expr.hir_id).map_or(false, |parent| {
         if let Some(Expr {
@@ -199,7 +196,10 @@ fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: boo
 /// If this expression is the option if let/else construct we're detecting, then
 /// this function returns an `OptionIfLetElseOccurence` struct with details if
 /// this construct is found, or None if this construct is not found.
-fn detect_option_if_let_else(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<OptionIfLetElseOccurence> {
+fn detect_option_if_let_else<'tcx>(
+    cx: &'_ LateContext<'tcx>,
+    expr: &'_ Expr<'tcx>,
+) -> Option<OptionIfLetElseOccurence> {
     if_chain! {
         if !utils::in_macro(expr.span); // Don't lint macros, because it behaves weirdly
         if let ExprKind::Match(cond_expr, arms, MatchSource::IfLetDesugar{contains_else_clause: true}) = &expr.kind;
@@ -214,10 +214,7 @@ fn detect_option_if_let_else(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<Op
             let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
             let some_body = extract_body_from_arm(&arms[0])?;
             let none_body = extract_body_from_arm(&arms[1])?;
-            let method_sugg = match &none_body.kind {
-                ExprKind::Block(..) => "map_or_else",
-                _ => "map_or",
-            };
+            let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) { "map_or" } else { "map_or_else" };
             let capture_name = id.name.to_ident_string();
             let wrap_braces = should_wrap_in_braces(cx, expr);
             let (as_ref, as_mut) = match &cond_expr.kind {
@@ -243,8 +240,8 @@ fn detect_option_if_let_else(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<Op
     }
 }
 
-impl<'a> LateLintPass<'a> for OptionIfLetElse {
-    fn check_expr(&mut self, cx: &LateContext<'a>, expr: &Expr<'_>) {
+impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
         if let Some(detection) = detect_option_if_let_else(cx, expr) {
             span_lint_and_sugg(
                 cx,