From dc13016ac2df1ce2663660389409b15eb2cf7e40 Mon Sep 17 00:00:00 2001 From: Eduardo Broto Date: Wed, 3 Jun 2020 01:13:57 +0200 Subject: [PATCH] Make let_and_return a late lint pass --- clippy_lints/src/let_and_return.rs | 82 ++++++++++++++++++++++++++++++ clippy_lints/src/lib.rs | 8 +-- clippy_lints/src/returns.rs | 82 ++---------------------------- src/lintlist/mod.rs | 2 +- 4 files changed, 91 insertions(+), 83 deletions(-) create mode 100644 clippy_lints/src/let_and_return.rs diff --git a/clippy_lints/src/let_and_return.rs b/clippy_lints/src/let_and_return.rs new file mode 100644 index 000000000..8b877f696 --- /dev/null +++ b/clippy_lints/src/let_and_return.rs @@ -0,0 +1,82 @@ +use if_chain::if_chain; +use rustc_errors::Applicability; +use rustc_hir::{Block, ExprKind, PatKind, StmtKind}; +use rustc_lint::{LateContext, LateLintPass, LintContext}; +use rustc_middle::lint::in_external_macro; +use rustc_session::{declare_lint_pass, declare_tool_lint}; + +use crate::utils::{in_macro, match_qpath, snippet_opt, span_lint_and_then}; + +declare_clippy_lint! { + /// **What it does:** Checks for `let`-bindings, which are subsequently + /// returned. + /// + /// **Why is this bad?** It is just extraneous code. Remove it to make your code + /// more rusty. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```rust + /// fn foo() -> String { + /// let x = String::new(); + /// x + /// } + /// ``` + /// instead, use + /// ``` + /// fn foo() -> String { + /// String::new() + /// } + /// ``` + pub LET_AND_RETURN, + style, + "creating a let-binding and then immediately returning it like `let x = expr; x` at the end of a block" +} + +declare_lint_pass!(LetReturn => [LET_AND_RETURN]); + +impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetReturn { + fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx Block<'_>) { + // we need both a let-binding stmt and an expr + if_chain! { + if let Some(retexpr) = block.expr; + if let Some(stmt) = block.stmts.iter().last(); + if let StmtKind::Local(local) = &stmt.kind; + if local.ty.is_none(); + if local.attrs.is_empty(); + if let Some(initexpr) = &local.init; + if let PatKind::Binding(.., ident, _) = local.pat.kind; + if let ExprKind::Path(qpath) = &retexpr.kind; + if match_qpath(qpath, &[&*ident.name.as_str()]); + if !in_external_macro(cx.sess(), initexpr.span); + if !in_external_macro(cx.sess(), retexpr.span); + if !in_external_macro(cx.sess(), local.span); + if !in_macro(local.span); + then { + span_lint_and_then( + cx, + LET_AND_RETURN, + retexpr.span, + "returning the result of a `let` binding from a block", + |err| { + err.span_label(local.span, "unnecessary `let` binding"); + + if let Some(snippet) = snippet_opt(cx, initexpr.span) { + err.multipart_suggestion( + "return the expression directly", + vec![ + (local.span, String::new()), + (retexpr.span, snippet), + ], + Applicability::MachineApplicable, + ); + } else { + err.span_help(initexpr.span, "this expression can be directly returned"); + } + }, + ); + } + } + } +} diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs index 6f8923b26..6bc9e23ba 100644 --- a/clippy_lints/src/lib.rs +++ b/clippy_lints/src/lib.rs @@ -239,6 +239,7 @@ mod large_const_arrays; mod large_enum_variant; mod large_stack_arrays; mod len_zero; +mod let_and_return; mod let_if_seq; mod let_underscore; mod lifetimes; @@ -596,6 +597,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: &large_stack_arrays::LARGE_STACK_ARRAYS, &len_zero::LEN_WITHOUT_IS_EMPTY, &len_zero::LEN_ZERO, + &let_and_return::LET_AND_RETURN, &let_if_seq::USELESS_LET_IF_SEQ, &let_underscore::LET_UNDERSCORE_LOCK, &let_underscore::LET_UNDERSCORE_MUST_USE, @@ -772,7 +774,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: ®ex::INVALID_REGEX, ®ex::REGEX_MACRO, ®ex::TRIVIAL_REGEX, - &returns::LET_AND_RETURN, &returns::NEEDLESS_RETURN, &returns::UNUSED_UNIT, &serde_api::SERDE_API_MISUSE, @@ -1022,6 +1023,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: store.register_early_pass(|| box formatting::Formatting); store.register_early_pass(|| box misc_early::MiscEarlyLints); store.register_early_pass(|| box returns::Return); + store.register_late_pass(|| box let_and_return::LetReturn); store.register_early_pass(|| box collapsible_if::CollapsibleIf); store.register_early_pass(|| box items_after_statements::ItemsAfterStatements); store.register_early_pass(|| box precedence::Precedence); @@ -1265,6 +1267,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&large_enum_variant::LARGE_ENUM_VARIANT), LintId::of(&len_zero::LEN_WITHOUT_IS_EMPTY), LintId::of(&len_zero::LEN_ZERO), + LintId::of(&let_and_return::LET_AND_RETURN), LintId::of(&let_underscore::LET_UNDERSCORE_LOCK), LintId::of(&lifetimes::EXTRA_UNUSED_LIFETIMES), LintId::of(&lifetimes::NEEDLESS_LIFETIMES), @@ -1390,7 +1393,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(®ex::INVALID_REGEX), LintId::of(®ex::REGEX_MACRO), LintId::of(®ex::TRIVIAL_REGEX), - LintId::of(&returns::LET_AND_RETURN), LintId::of(&returns::NEEDLESS_RETURN), LintId::of(&returns::UNUSED_UNIT), LintId::of(&serde_api::SERDE_API_MISUSE), @@ -1474,6 +1476,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&inherent_to_string::INHERENT_TO_STRING), LintId::of(&len_zero::LEN_WITHOUT_IS_EMPTY), LintId::of(&len_zero::LEN_ZERO), + LintId::of(&let_and_return::LET_AND_RETURN), LintId::of(&literal_representation::INCONSISTENT_DIGIT_GROUPING), LintId::of(&loops::EMPTY_LOOP), LintId::of(&loops::FOR_KV_MAP), @@ -1526,7 +1529,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&redundant_static_lifetimes::REDUNDANT_STATIC_LIFETIMES), LintId::of(®ex::REGEX_MACRO), LintId::of(®ex::TRIVIAL_REGEX), - LintId::of(&returns::LET_AND_RETURN), LintId::of(&returns::NEEDLESS_RETURN), LintId::of(&returns::UNUSED_UNIT), LintId::of(&single_component_path_imports::SINGLE_COMPONENT_PATH_IMPORTS), diff --git a/clippy_lints/src/returns.rs b/clippy_lints/src/returns.rs index 35464f629..3c9397441 100644 --- a/clippy_lints/src/returns.rs +++ b/clippy_lints/src/returns.rs @@ -8,7 +8,7 @@ use rustc_session::{declare_lint_pass, declare_tool_lint}; use rustc_span::source_map::Span; use rustc_span::BytePos; -use crate::utils::{in_macro, match_path_ast, snippet_opt, span_lint_and_sugg, span_lint_and_then}; +use crate::utils::{snippet_opt, span_lint_and_sugg, span_lint_and_then}; declare_clippy_lint! { /// **What it does:** Checks for return statements at the end of a block. @@ -36,33 +36,6 @@ declare_clippy_lint! { "using a return statement like `return expr;` where an expression would suffice" } -declare_clippy_lint! { - /// **What it does:** Checks for `let`-bindings, which are subsequently - /// returned. - /// - /// **Why is this bad?** It is just extraneous code. Remove it to make your code - /// more rusty. - /// - /// **Known problems:** None. - /// - /// **Example:** - /// ```rust - /// fn foo() -> String { - /// let x = String::new(); - /// x - /// } - /// ``` - /// instead, use - /// ``` - /// fn foo() -> String { - /// String::new() - /// } - /// ``` - pub LET_AND_RETURN, - style, - "creating a let-binding and then immediately returning it like `let x = expr; x` at the end of a block" -} - declare_clippy_lint! { /// **What it does:** Checks for unit (`()`) expressions that can be removed. /// @@ -90,7 +63,7 @@ enum RetReplacement { Block, } -declare_lint_pass!(Return => [NEEDLESS_RETURN, LET_AND_RETURN, UNUSED_UNIT]); +declare_lint_pass!(Return => [NEEDLESS_RETURN, UNUSED_UNIT]); impl Return { // Check the final stmt or expr in a block for unnecessary return. @@ -105,7 +78,7 @@ impl Return { } } - // Check a the final expression in a block if it's a return. + // Check the final expression in a block if it's a return. fn check_final_expr( &mut self, cx: &EarlyContext<'_>, @@ -186,54 +159,6 @@ impl Return { }, } } - - // Check for "let x = EXPR; x" - fn check_let_return(cx: &EarlyContext<'_>, block: &ast::Block) { - let mut it = block.stmts.iter(); - - // we need both a let-binding stmt and an expr - if_chain! { - if let Some(retexpr) = it.next_back(); - if let ast::StmtKind::Expr(ref retexpr) = retexpr.kind; - if let Some(stmt) = it.next_back(); - if let ast::StmtKind::Local(ref local) = stmt.kind; - // don't lint in the presence of type inference - if local.ty.is_none(); - if local.attrs.is_empty(); - if let Some(ref initexpr) = local.init; - if let ast::PatKind::Ident(_, ident, _) = local.pat.kind; - if let ast::ExprKind::Path(_, ref path) = retexpr.kind; - if match_path_ast(path, &[&*ident.name.as_str()]); - if !in_external_macro(cx.sess(), initexpr.span); - if !in_external_macro(cx.sess(), retexpr.span); - if !in_external_macro(cx.sess(), local.span); - if !in_macro(local.span); - then { - span_lint_and_then( - cx, - LET_AND_RETURN, - retexpr.span, - "returning the result of a `let` binding from a block", - |err| { - err.span_label(local.span, "unnecessary `let` binding"); - - if let Some(snippet) = snippet_opt(cx, initexpr.span) { - err.multipart_suggestion( - "return the expression directly", - vec![ - (local.span, String::new()), - (retexpr.span, snippet), - ], - Applicability::MachineApplicable, - ); - } else { - err.span_help(initexpr.span, "this expression can be directly returned"); - } - }, - ); - } - } - } } impl EarlyLintPass for Return { @@ -254,7 +179,6 @@ impl EarlyLintPass for Return { } fn check_block(&mut self, cx: &EarlyContext<'_>, block: &ast::Block) { - Self::check_let_return(cx, block); if_chain! { if let Some(ref stmt) = block.stmts.last(); if let ast::StmtKind::Expr(ref expr) = stmt.kind; diff --git a/src/lintlist/mod.rs b/src/lintlist/mod.rs index d5d07ccb2..bb191f9be 100644 --- a/src/lintlist/mod.rs +++ b/src/lintlist/mod.rs @@ -1023,7 +1023,7 @@ pub static ref ALL_LINTS: Vec = vec![ group: "style", desc: "creating a let-binding and then immediately returning it like `let x = expr; x` at the end of a block", deprecation: None, - module: "returns", + module: "let_and_return", }, Lint { name: "let_underscore_lock",