Merge commit '6ed6f1e6a1' into clippyup

clippy_lints/src/methods/unnecessary_fold.rs

@@ -0,0 +1,101 @@
+use crate::utils::{
+    match_trait_method, path_to_local_id, paths, remove_blocks, snippet_with_applicability, span_lint_and_sugg,
+    strip_pat_refs,
+};
+use if_chain::if_chain;
+use rustc_ast::ast;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_hir::PatKind;
+use rustc_lint::LateContext;
+use rustc_span::source_map::Span;
+
+use super::UNNECESSARY_FOLD;
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, fold_args: &[hir::Expr<'_>], fold_span: Span) {
+    fn check_fold_with_op(
+        cx: &LateContext<'_>,
+        expr: &hir::Expr<'_>,
+        fold_args: &[hir::Expr<'_>],
+        fold_span: Span,
+        op: hir::BinOpKind,
+        replacement_method_name: &str,
+        replacement_has_args: bool,
+    ) {
+        if_chain! {
+            // Extract the body of the closure passed to fold
+            if let hir::ExprKind::Closure(_, _, body_id, _, _) = fold_args[2].kind;
+            let closure_body = cx.tcx.hir().body(body_id);
+            let closure_expr = remove_blocks(&closure_body.value);
+
+            // Check if the closure body is of the form `acc <op> some_expr(x)`
+            if let hir::ExprKind::Binary(ref bin_op, ref left_expr, ref right_expr) = closure_expr.kind;
+            if bin_op.node == op;
+
+            // Extract the names of the two arguments to the closure
+            if let [param_a, param_b] = closure_body.params;
+            if let PatKind::Binding(_, first_arg_id, ..) = strip_pat_refs(&param_a.pat).kind;
+            if let PatKind::Binding(_, second_arg_id, second_arg_ident, _) = strip_pat_refs(&param_b.pat).kind;
+
+            if path_to_local_id(left_expr, first_arg_id);
+            if replacement_has_args || path_to_local_id(right_expr, second_arg_id);
+
+            then {
+                let mut applicability = Applicability::MachineApplicable;
+                let sugg = if replacement_has_args {
+                    format!(
+                        "{replacement}(|{s}| {r})",
+                        replacement = replacement_method_name,
+                        s = second_arg_ident,
+                        r = snippet_with_applicability(cx, right_expr.span, "EXPR", &mut applicability),
+                    )
+                } else {
+                    format!(
+                        "{replacement}()",
+                        replacement = replacement_method_name,
+                    )
+                };
+
+                span_lint_and_sugg(
+                    cx,
+                    UNNECESSARY_FOLD,
+                    fold_span.with_hi(expr.span.hi()),
+                    // TODO #2371 don't suggest e.g., .any(|x| f(x)) if we can suggest .any(f)
+                    "this `.fold` can be written more succinctly using another method",
+                    "try",
+                    sugg,
+                    applicability,
+                );
+            }
+        }
+    }
+
+    // Check that this is a call to Iterator::fold rather than just some function called fold
+    if !match_trait_method(cx, expr, &paths::ITERATOR) {
+        return;
+    }
+
+    assert!(
+        fold_args.len() == 3,
+        "Expected fold_args to have three entries - the receiver, the initial value and the closure"
+    );
+
+    // Check if the first argument to .fold is a suitable literal
+    if let hir::ExprKind::Lit(ref lit) = fold_args[1].kind {
+        match lit.node {
+            ast::LitKind::Bool(false) => {
+                check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Or, "any", true)
+            },
+            ast::LitKind::Bool(true) => {
+                check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::And, "all", true)
+            },
+            ast::LitKind::Int(0, _) => {
+                check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Add, "sum", false)
+            },
+            ast::LitKind::Int(1, _) => {
+                check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Mul, "product", false)
+            },
+            _ => (),
+        }
+    }
+}