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Auto merge of rust-lang#5694 - wangtheo:issue-5626, r=matthiaskrgr
rust-lang#5626: lint iterator.map(|x| x) changelog: adds a new lint for iterator.map(|x| x) (see rust-lang/rust-clippy#5626) The code also lints for result.map(|x| x) and option.map(|x| x). Also, I'm not sure if I'm checking for type adjustments correctly and I can't think of an example where .map(|x| x) would apply type adjustments.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,126 @@ | ||
| use crate::utils::{ | ||
| is_adjusted, is_type_diagnostic_item, match_path, match_trait_method, match_var, paths, remove_blocks, | ||
| span_lint_and_sugg, | ||
| }; | ||
| use if_chain::if_chain; | ||
| use rustc_errors::Applicability; | ||
| use rustc_hir::{Body, Expr, ExprKind, Pat, PatKind, QPath, StmtKind}; | ||
| use rustc_lint::{LateContext, LateLintPass}; | ||
| use rustc_session::{declare_lint_pass, declare_tool_lint}; | ||
|
|
||
| declare_clippy_lint! { | ||
| /// **What it does:** Checks for instances of `map(f)` where `f` is the identity function. | ||
| /// | ||
| /// **Why is this bad?** It can be written more concisely without the call to `map`. | ||
| /// | ||
| /// **Known problems:** None. | ||
| /// | ||
| /// **Example:** | ||
| /// | ||
| /// ```rust | ||
| /// let x = [1, 2, 3]; | ||
| /// let y: Vec<_> = x.iter().map(|x| x).map(|x| 2*x).collect(); | ||
| /// ``` | ||
| /// Use instead: | ||
| /// ```rust | ||
| /// let x = [1, 2, 3]; | ||
| /// let y: Vec<_> = x.iter().map(|x| 2*x).collect(); | ||
| /// ``` | ||
| pub MAP_IDENTITY, | ||
| complexity, | ||
| "using iterator.map(|x| x)" | ||
| } | ||
|
|
||
| declare_lint_pass!(MapIdentity => [MAP_IDENTITY]); | ||
|
|
||
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MapIdentity { | ||
| fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &Expr<'_>) { | ||
| if expr.span.from_expansion() { | ||
| return; | ||
| } | ||
|
|
||
| if_chain! { | ||
| if let Some([caller, func]) = get_map_argument(cx, expr); | ||
| if is_expr_identity_function(cx, func); | ||
| then { | ||
| span_lint_and_sugg( | ||
| cx, | ||
| MAP_IDENTITY, | ||
| expr.span.trim_start(caller.span).unwrap(), | ||
| "unnecessary map of the identity function", | ||
| "remove the call to `map`", | ||
| String::new(), | ||
| Applicability::MachineApplicable | ||
| ) | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// Returns the arguments passed into map() if the expression is a method call to | ||
| /// map(). Otherwise, returns None. | ||
| fn get_map_argument<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr<'a>) -> Option<&'a [Expr<'a>]> { | ||
| if_chain! { | ||
| if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind; | ||
| if args.len() == 2 && method.ident.as_str() == "map"; | ||
| let caller_ty = cx.tables.expr_ty(&args[0]); | ||
| if match_trait_method(cx, expr, &paths::ITERATOR) | ||
| || is_type_diagnostic_item(cx, caller_ty, sym!(result_type)) | ||
| || is_type_diagnostic_item(cx, caller_ty, sym!(option_type)); | ||
| then { | ||
| Some(args) | ||
| } else { | ||
| None | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// Checks if an expression represents the identity function | ||
| /// Only examines closures and `std::convert::identity` | ||
| fn is_expr_identity_function(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool { | ||
| match expr.kind { | ||
| ExprKind::Closure(_, _, body_id, _, _) => is_body_identity_function(cx, cx.tcx.hir().body(body_id)), | ||
| ExprKind::Path(QPath::Resolved(_, ref path)) => match_path(path, &paths::STD_CONVERT_IDENTITY), | ||
| _ => false, | ||
| } | ||
| } | ||
|
|
||
| /// Checks if a function's body represents the identity function | ||
| /// Looks for bodies of the form `|x| x`, `|x| return x`, `|x| { return x }` or `|x| { | ||
| /// return x; }` | ||
| fn is_body_identity_function(cx: &LateContext<'_, '_>, func: &Body<'_>) -> bool { | ||
| let params = func.params; | ||
| let body = remove_blocks(&func.value); | ||
|
|
||
| // if there's less/more than one parameter, then it is not the identity function | ||
| if params.len() != 1 { | ||
| return false; | ||
| } | ||
|
|
||
| match body.kind { | ||
| ExprKind::Path(QPath::Resolved(None, _)) => match_expr_param(cx, body, params[0].pat), | ||
| ExprKind::Ret(Some(ref ret_val)) => match_expr_param(cx, ret_val, params[0].pat), | ||
| ExprKind::Block(ref block, _) => { | ||
| if_chain! { | ||
| if block.stmts.len() == 1; | ||
| if let StmtKind::Semi(ref expr) | StmtKind::Expr(ref expr) = block.stmts[0].kind; | ||
| if let ExprKind::Ret(Some(ref ret_val)) = expr.kind; | ||
| then { | ||
| match_expr_param(cx, ret_val, params[0].pat) | ||
| } else { | ||
| false | ||
| } | ||
| } | ||
| }, | ||
| _ => false, | ||
| } | ||
| } | ||
|
|
||
| /// Returns true iff an expression returns the same thing as a parameter's pattern | ||
| fn match_expr_param(cx: &LateContext<'_, '_>, expr: &Expr<'_>, pat: &Pat<'_>) -> bool { | ||
| if let PatKind::Binding(_, _, ident, _) = pat.kind { | ||
| match_var(expr, ident.name) && !(cx.tables.hir_owner == Some(expr.hir_id.owner) && is_adjusted(cx, expr)) | ||
| } else { | ||
| false | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,23 @@ | ||
| // run-rustfix | ||
| #![warn(clippy::map_identity)] | ||
| #![allow(clippy::needless_return)] | ||
|
|
||
| fn main() { | ||
| let x: [u16; 3] = [1, 2, 3]; | ||
| // should lint | ||
| let _: Vec<_> = x.iter().map(not_identity).collect(); | ||
| let _: Vec<_> = x.iter().collect(); | ||
| let _: Option<u8> = Some(3); | ||
| let _: Result<i8, f32> = Ok(-3); | ||
| // should not lint | ||
| let _: Vec<_> = x.iter().map(|x| 2 * x).collect(); | ||
| let _: Vec<_> = x.iter().map(not_identity).map(|x| return x - 4).collect(); | ||
| let _: Option<u8> = None.map(|x: u8| x - 1); | ||
| let _: Result<i8, f32> = Err(2.3).map(|x: i8| { | ||
| return x + 3; | ||
| }); | ||
| } | ||
|
|
||
| fn not_identity(x: &u16) -> u16 { | ||
| *x | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,25 @@ | ||
| // run-rustfix | ||
| #![warn(clippy::map_identity)] | ||
| #![allow(clippy::needless_return)] | ||
|
|
||
| fn main() { | ||
| let x: [u16; 3] = [1, 2, 3]; | ||
| // should lint | ||
| let _: Vec<_> = x.iter().map(not_identity).map(|x| return x).collect(); | ||
| let _: Vec<_> = x.iter().map(std::convert::identity).map(|y| y).collect(); | ||
| let _: Option<u8> = Some(3).map(|x| x); | ||
| let _: Result<i8, f32> = Ok(-3).map(|x| { | ||
| return x; | ||
| }); | ||
| // should not lint | ||
| let _: Vec<_> = x.iter().map(|x| 2 * x).collect(); | ||
| let _: Vec<_> = x.iter().map(not_identity).map(|x| return x - 4).collect(); | ||
| let _: Option<u8> = None.map(|x: u8| x - 1); | ||
| let _: Result<i8, f32> = Err(2.3).map(|x: i8| { | ||
| return x + 3; | ||
| }); | ||
| } | ||
|
|
||
| fn not_identity(x: &u16) -> u16 { | ||
| *x | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,37 @@ | ||
| error: unnecessary map of the identity function | ||
| --> $DIR/map_identity.rs:8:47 | ||
| | | ||
| LL | let _: Vec<_> = x.iter().map(not_identity).map(|x| return x).collect(); | ||
| | ^^^^^^^^^^^^^^^^^^ help: remove the call to `map` | ||
| | | ||
| = note: `-D clippy::map-identity` implied by `-D warnings` | ||
|
|
||
| error: unnecessary map of the identity function | ||
| --> $DIR/map_identity.rs:9:57 | ||
| | | ||
| LL | let _: Vec<_> = x.iter().map(std::convert::identity).map(|y| y).collect(); | ||
| | ^^^^^^^^^^^ help: remove the call to `map` | ||
|
|
||
| error: unnecessary map of the identity function | ||
| --> $DIR/map_identity.rs:9:29 | ||
| | | ||
| LL | let _: Vec<_> = x.iter().map(std::convert::identity).map(|y| y).collect(); | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove the call to `map` | ||
|
|
||
| error: unnecessary map of the identity function | ||
| --> $DIR/map_identity.rs:10:32 | ||
| | | ||
| LL | let _: Option<u8> = Some(3).map(|x| x); | ||
| | ^^^^^^^^^^^ help: remove the call to `map` | ||
|
|
||
| error: unnecessary map of the identity function | ||
| --> $DIR/map_identity.rs:11:36 | ||
| | | ||
| LL | let _: Result<i8, f32> = Ok(-3).map(|x| { | ||
| | ____________________________________^ | ||
| LL | | return x; | ||
| LL | | }); | ||
| | |______^ help: remove the call to `map` | ||
|
|
||
| error: aborting due to 5 previous errors | ||
|
|