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https://github.com/rust-lang/rust-clippy
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Merge pull request #132 from birkenfeld/let_and_return
New lint: let and immediately return
This commit is contained in:
commit
7c14b5b67f
5 changed files with 148 additions and 71 deletions
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@ -31,6 +31,7 @@ Lints included in this crate:
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- `zero_width_space`: Warns on encountering a unicode zero-width space
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- `string_add_assign`: Warns on `x = x + ..` where `x` is a `String` and suggests using `push_str(..)` instead.
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- `needless_return`: Warns on using `return expr;` when a simple `expr` would suffice.
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- `let_and_return`: Warns on doing `let x = expr; x` at the end of a function.
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- `option_unwrap_used`: Warns when `Option.unwrap()` is used, and suggests `.expect()`.
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- `result_unwrap_used`: Warns when `Result.unwrap()` is used (silent by default).
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- `modulo_one`: Warns on taking a number modulo 1, which always has a result of 0.
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@ -30,6 +30,7 @@ pub mod unicode;
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pub mod utils;
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pub mod strings;
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pub mod methods;
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pub mod returns;
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#[plugin_registrar]
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pub fn plugin_registrar(reg: &mut Registry) {
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@ -55,7 +56,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
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reg.register_lint_pass(box misc::ModuloOne as LintPassObject);
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reg.register_lint_pass(box unicode::Unicode as LintPassObject);
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reg.register_lint_pass(box strings::StringAdd as LintPassObject);
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reg.register_lint_pass(box misc::NeedlessReturn as LintPassObject);
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reg.register_lint_pass(box returns::ReturnPass as LintPassObject);
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reg.register_lint_pass(box methods::MethodsPass as LintPassObject);
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reg.register_lint_group("clippy", vec![types::BOX_VEC, types::LINKEDLIST,
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@ -77,7 +78,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
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collapsible_if::COLLAPSIBLE_IF,
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unicode::ZERO_WIDTH_SPACE,
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strings::STRING_ADD_ASSIGN,
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misc::NEEDLESS_RETURN,
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returns::NEEDLESS_RETURN,
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misc::MODULO_ONE,
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methods::OPTION_UNWRAP_USED,
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methods::RESULT_UNWRAP_USED,
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69
src/misc.rs
69
src/misc.rs
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@ -270,75 +270,6 @@ fn is_str_arg(cx: &Context, args: &[P<Expr>]) -> bool {
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walk_ptrs_ty(cx.tcx.expr_ty(&*args[0])).sty { true } else { false }
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}
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declare_lint!(pub NEEDLESS_RETURN, Warn,
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"Warn on using a return statement where an expression would be enough");
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#[derive(Copy,Clone)]
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pub struct NeedlessReturn;
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impl NeedlessReturn {
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// Check the final stmt or expr in a block for unnecessary return.
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fn check_block_return(&mut self, cx: &Context, block: &Block) {
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if let Some(ref expr) = block.expr {
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self.check_final_expr(cx, expr);
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} else if let Some(stmt) = block.stmts.last() {
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if let StmtSemi(ref expr, _) = stmt.node {
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if let ExprRet(Some(ref inner)) = expr.node {
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self.emit_lint(cx, (expr.span, inner.span));
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}
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}
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}
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}
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// Check a the final expression in a block if it's a return.
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fn check_final_expr(&mut self, cx: &Context, expr: &Expr) {
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match expr.node {
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// simple return is always "bad"
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ExprRet(Some(ref inner)) => {
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self.emit_lint(cx, (expr.span, inner.span));
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}
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// a whole block? check it!
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ExprBlock(ref block) => {
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self.check_block_return(cx, block);
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}
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// an if/if let expr, check both exprs
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// note, if without else is going to be a type checking error anyways
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// (except for unit type functions) so we don't match it
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ExprIf(_, ref ifblock, Some(ref elsexpr)) |
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ExprIfLet(_, _, ref ifblock, Some(ref elsexpr)) => {
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self.check_block_return(cx, ifblock);
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self.check_final_expr(cx, elsexpr);
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}
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// a match expr, check all arms
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ExprMatch(_, ref arms, _) => {
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for arm in arms {
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self.check_final_expr(cx, &*arm.body);
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}
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}
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_ => { }
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}
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}
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fn emit_lint(&mut self, cx: &Context, spans: (Span, Span)) {
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span_lint(cx, NEEDLESS_RETURN, spans.0, &format!(
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"unneeded return statement. Consider using {} \
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without the trailing semicolon",
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snippet(cx, spans.1, "..")))
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}
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}
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impl LintPass for NeedlessReturn {
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fn get_lints(&self) -> LintArray {
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lint_array!(NEEDLESS_RETURN)
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}
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fn check_fn(&mut self, cx: &Context, _: FnKind, _: &FnDecl,
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block: &Block, _: Span, _: ast::NodeId) {
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self.check_block_return(cx, block);
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}
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}
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declare_lint!(pub MODULO_ONE, Warn, "Warn on expressions that include % 1, which is always 0");
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#[derive(Copy,Clone)]
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110
src/returns.rs
Normal file
110
src/returns.rs
Normal file
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@ -0,0 +1,110 @@
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use syntax::ast;
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use syntax::ast::*;
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use syntax::codemap::{Span, Spanned};
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use syntax::visit::FnKind;
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use rustc::lint::{Context, LintPass, LintArray, Level};
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use utils::{span_lint, snippet, match_path};
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declare_lint!(pub NEEDLESS_RETURN, Warn,
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"Warn on using a return statement where an expression would be enough");
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declare_lint!(pub LET_AND_RETURN, Warn,
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"Warn on creating a let-binding and then immediately returning it");
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#[derive(Copy,Clone)]
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pub struct ReturnPass;
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impl ReturnPass {
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// Check the final stmt or expr in a block for unnecessary return.
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fn check_block_return(&mut self, cx: &Context, block: &Block) {
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if let Some(ref expr) = block.expr {
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self.check_final_expr(cx, expr);
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} else if let Some(stmt) = block.stmts.last() {
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if let StmtSemi(ref expr, _) = stmt.node {
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if let ExprRet(Some(ref inner)) = expr.node {
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self.emit_return_lint(cx, (expr.span, inner.span));
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}
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}
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}
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}
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// Check a the final expression in a block if it's a return.
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fn check_final_expr(&mut self, cx: &Context, expr: &Expr) {
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match expr.node {
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// simple return is always "bad"
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ExprRet(Some(ref inner)) => {
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self.emit_return_lint(cx, (expr.span, inner.span));
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}
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// a whole block? check it!
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ExprBlock(ref block) => {
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self.check_block_return(cx, block);
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}
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// an if/if let expr, check both exprs
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// note, if without else is going to be a type checking error anyways
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// (except for unit type functions) so we don't match it
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ExprIf(_, ref ifblock, Some(ref elsexpr)) |
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ExprIfLet(_, _, ref ifblock, Some(ref elsexpr)) => {
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self.check_block_return(cx, ifblock);
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self.check_final_expr(cx, elsexpr);
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}
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// a match expr, check all arms
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ExprMatch(_, ref arms, _) => {
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for arm in arms {
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self.check_final_expr(cx, &*arm.body);
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}
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}
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_ => { }
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}
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}
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fn emit_return_lint(&mut self, cx: &Context, spans: (Span, Span)) {
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span_lint(cx, NEEDLESS_RETURN, spans.0, &format!(
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"unneeded return statement. Consider using {} \
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without the trailing semicolon",
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snippet(cx, spans.1, "..")))
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}
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// Check for "let x = EXPR; x"
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fn check_let_return(&mut self, cx: &Context, block: &Block) {
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// we need both a let-binding stmt and an expr
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if let Some(stmt) = block.stmts.last() {
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if let StmtDecl(ref decl, _) = stmt.node {
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if let DeclLocal(ref local) = decl.node {
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if let Some(ref initexpr) = local.init {
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if let PatIdent(_, Spanned { node: id, .. }, _) = local.pat.node {
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if let Some(ref retexpr) = block.expr {
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if let ExprPath(_, ref path) = retexpr.node {
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if match_path(path, &[&*id.name.as_str()]) {
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self.emit_let_lint(cx, retexpr.span, initexpr.span);
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}
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}
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}
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}
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}
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}
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}
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}
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}
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fn emit_let_lint(&mut self, cx: &Context, lint_span: Span, note_span: Span) {
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span_lint(cx, LET_AND_RETURN, lint_span,
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"returning the result of a let binding. \
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Consider returning the expression directly.");
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if cx.current_level(LET_AND_RETURN) != Level::Allow {
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cx.sess().span_note(note_span,
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"this expression can be directly returned");
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}
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}
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}
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impl LintPass for ReturnPass {
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fn get_lints(&self) -> LintArray {
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lint_array!(NEEDLESS_RETURN, LET_AND_RETURN)
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}
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fn check_fn(&mut self, cx: &Context, _: FnKind, _: &FnDecl,
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block: &Block, _: Span, _: ast::NodeId) {
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self.check_block_return(cx, block);
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self.check_let_return(cx, block);
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}
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}
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34
tests/compile-fail/let_return.rs
Executable file
34
tests/compile-fail/let_return.rs
Executable file
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@ -0,0 +1,34 @@
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#![feature(plugin)]
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#![plugin(clippy)]
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#![deny(let_and_return)]
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fn test() -> i32 {
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let _y = 0; // no warning
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let x = 5; //~NOTE
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x //~ERROR:
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}
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fn test_nowarn_1() -> i32 {
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let mut x = 5;
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x += 1;
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x
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}
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fn test_nowarn_2() -> i32 {
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let x = 5;
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x + 1
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}
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fn test_nowarn_3() -> (i32, i32) {
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// this should technically warn, but we do not compare complex patterns
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let (x, y) = (5, 9);
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(x, y)
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}
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fn main() {
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test();
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test_nowarn_1();
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test_nowarn_2();
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test_nowarn_3();
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}
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