use rustc::lint::*;
-use syntax::ast::*;
-use syntax::codemap::{Span, Spanned};
+use rustc::{declare_lint, lint_array};
+use if_chain::if_chain;
+use syntax::ast;
+use syntax::codemap::Span;
use syntax::visit::FnKind;
-use utils::{span_note_and_lint, span_lint_and_then, snippet_opt, match_path_ast, in_external_macro};
+use crate::utils::{in_external_macro, in_macro, match_path_ast, snippet_opt, span_lint_and_then, span_note_and_lint};
-/// **What it does:** This lint checks for return statements at the end of a block.
+/// **What it does:** Checks for return statements at the end of a block.
///
-/// **Why is this bad?** Removing the `return` and semicolon will make the code more rusty.
+/// **Why is this bad?** Removing the `return` and semicolon will make the code
+/// more rusty.
///
-/// **Known problems:** Following this lint's advice may currently run afoul of Rust issue [#31439](https://github.com/rust-lang/rust/issues/31439), so if you get lifetime errors, please roll back the change until that issue is fixed.
+/// **Known problems:** If the computation returning the value borrows a local
+/// variable, removing the `return` may run afoul of the borrow checker.
///
-/// **Example:** `fn foo(x: usize) { return x; }`
-declare_lint! {
- pub NEEDLESS_RETURN, Warn,
+/// **Example:**
+/// ```rust
+/// fn foo(x: usize) { return x; }
+/// ```
+declare_clippy_lint! {
+ pub NEEDLESS_RETURN,
+ style,
"using a return statement like `return expr;` where an expression would suffice"
}
-/// **What it does:** This lint checks for `let`-bindings, which are subsequently returned.
+/// **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.
+/// **Why is this bad?** It is just extraneous code. Remove it to make your code
+/// more rusty.
///
-/// **Known problems:** Following this lint's advice may currently run afoul of Rust issue [#31439](https://github.com/rust-lang/rust/issues/31439), so if you get lifetime errors, please roll back the change until that issue is fixed.
+/// **Known problems:** None.
///
-/// **Example:** `{ let x = ..; x }`
-declare_lint! {
- pub LET_AND_RETURN, Warn,
+/// **Example:**
+/// ```rust
+/// { let x = ..; x }
+/// ```
+declare_clippy_lint! {
+ 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"
}
impl ReturnPass {
// Check the final stmt or expr in a block for unnecessary return.
- fn check_block_return(&mut self, cx: &EarlyContext, block: &Block) {
+ fn check_block_return(&mut self, cx: &EarlyContext, block: &ast::Block) {
if let Some(stmt) = block.stmts.last() {
match stmt.node {
- StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => {
+ ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => {
self.check_final_expr(cx, expr, Some(stmt.span));
- }
+ },
_ => (),
}
}
}
// Check a the final expression in a block if it's a return.
- fn check_final_expr(&mut self, cx: &EarlyContext, expr: &Expr, span: Option<Span>) {
+ fn check_final_expr(&mut self, cx: &EarlyContext, expr: &ast::Expr, span: Option<Span>) {
match expr.node {
// simple return is always "bad"
- ExprKind::Ret(Some(ref inner)) => {
- self.emit_return_lint(cx, span.expect("`else return` is not possible"), inner.span);
- }
+ ast::ExprKind::Ret(Some(ref inner)) => {
+ // allow `#[cfg(a)] return a; #[cfg(b)] return b;`
+ if !expr.attrs.iter().any(attr_is_cfg) {
+ self.emit_return_lint(cx, span.expect("`else return` is not possible"), inner.span);
+ }
+ },
// a whole block? check it!
- ExprKind::Block(ref block) => {
+ ast::ExprKind::Block(ref block, _) => {
self.check_block_return(cx, block);
- }
+ },
// an if/if let expr, check both exprs
// note, if without else is going to be a type checking error anyways
// (except for unit type functions) so we don't match it
- ExprKind::If(_, ref ifblock, Some(ref elsexpr)) => {
+ ast::ExprKind::If(_, ref ifblock, Some(ref elsexpr)) => {
self.check_block_return(cx, ifblock);
self.check_final_expr(cx, elsexpr, None);
- }
+ },
// a match expr, check all arms
- ExprKind::Match(_, ref arms) => {
- for arm in arms {
- self.check_final_expr(cx, &arm.body, Some(arm.body.span));
- }
- }
+ ast::ExprKind::Match(_, ref arms) => for arm in arms {
+ self.check_final_expr(cx, &arm.body, Some(arm.body.span));
+ },
_ => (),
}
}
fn emit_return_lint(&mut self, cx: &EarlyContext, ret_span: Span, inner_span: Span) {
- if in_external_macro(cx, inner_span) {
+ if in_external_macro(cx, inner_span) || in_macro(inner_span) {
return;
}
span_lint_and_then(cx, NEEDLESS_RETURN, ret_span, "unneeded return statement", |db| {
if let Some(snippet) = snippet_opt(cx, inner_span) {
- db.span_suggestion(ret_span, "remove `return` as shown:", snippet);
+ db.span_suggestion(ret_span, "remove `return` as shown", snippet);
}
});
}
// Check for "let x = EXPR; x"
- fn check_let_return(&mut self, cx: &EarlyContext, block: &Block) {
+ fn check_let_return(&mut self, cx: &EarlyContext, block: &ast::Block) {
let mut it = block.stmts.iter();
// we need both a let-binding stmt and an expr
- if_let_chain! {[
- let Some(ref retexpr) = it.next_back(),
- let StmtKind::Expr(ref retexpr) = retexpr.node,
- let Some(stmt) = it.next_back(),
- let StmtKind::Local(ref local) = stmt.node,
- let Some(ref initexpr) = local.init,
- let PatKind::Ident(_, Spanned { node: id, .. }, _) = local.pat.node,
- let ExprKind::Path(_, ref path) = retexpr.node,
- match_path_ast(path, &[&id.name.as_str()]),
- !in_external_macro(cx, initexpr.span),
- ], {
- span_note_and_lint(cx,
- LET_AND_RETURN,
- retexpr.span,
- "returning the result of a let binding from a block. \
- Consider returning the expression directly.",
- initexpr.span,
- "this expression can be directly returned");
- }}
+ if_chain! {
+ if let Some(retexpr) = it.next_back();
+ if let ast::StmtKind::Expr(ref retexpr) = retexpr.node;
+ if let Some(stmt) = it.next_back();
+ if let ast::StmtKind::Local(ref local) = stmt.node;
+ // don't lint in the presence of type inference
+ if local.ty.is_none();
+ if !local.attrs.iter().any(attr_is_cfg);
+ if let Some(ref initexpr) = local.init;
+ if let ast::PatKind::Ident(_, ident, _) = local.pat.node;
+ if let ast::ExprKind::Path(_, ref path) = retexpr.node;
+ if match_path_ast(path, &[&ident.as_str()]);
+ if !in_external_macro(cx, initexpr.span);
+ then {
+ span_note_and_lint(cx,
+ LET_AND_RETURN,
+ retexpr.span,
+ "returning the result of a let binding from a block. \
+ Consider returning the expression directly.",
+ initexpr.span,
+ "this expression can be directly returned");
+ }
+ }
}
}
}
impl EarlyLintPass for ReturnPass {
- fn check_fn(&mut self, cx: &EarlyContext, _: FnKind, _: &FnDecl, block: &Block, _: Span, _: NodeId) {
- self.check_block_return(cx, block);
+ fn check_fn(&mut self, cx: &EarlyContext, kind: FnKind, _: &ast::FnDecl, _: Span, _: ast::NodeId) {
+ match kind {
+ FnKind::ItemFn(.., block) | FnKind::Method(.., block) => self.check_block_return(cx, block),
+ FnKind::Closure(body) => self.check_final_expr(cx, body, Some(body.span)),
+ }
}
- fn check_block(&mut self, cx: &EarlyContext, block: &Block) {
+ fn check_block(&mut self, cx: &EarlyContext, block: &ast::Block) {
self.check_let_return(cx, block);
}
}
+
+fn attr_is_cfg(attr: &ast::Attribute) -> bool {
+ attr.meta_item_list().is_some() && attr.name() == "cfg"
+}
projects / rust.git / blobdiff