fe8068c41b
Breakages for introduced by rust pull request 'AST: Give spans to all identifies' - rust-lang/rust/pull#49154 Closes #2639
154 lines
5.6 KiB
Rust
154 lines
5.6 KiB
Rust
use rustc::lint::*;
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use syntax::ast;
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use syntax::codemap::Span;
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use syntax::visit::FnKind;
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use utils::{in_external_macro, in_macro, match_path_ast, snippet_opt, span_lint_and_then, span_note_and_lint};
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/// **What it does:** Checks for return statements at the end of a block.
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///
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/// **Why is this bad?** Removing the `return` and semicolon will make the code
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/// more rusty.
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///
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/// **Known problems:** If the computation returning the value borrows a local
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/// variable, removing the `return` may run afoul of the borrow checker.
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///
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/// **Example:**
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/// ```rust
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/// fn foo(x: usize) { return x; }
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/// ```
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declare_clippy_lint! {
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pub NEEDLESS_RETURN,
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style,
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"using a return statement like `return expr;` where an expression would suffice"
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}
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/// **What it does:** Checks for `let`-bindings, which are subsequently
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/// returned.
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///
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/// **Why is this bad?** It is just extraneous code. Remove it to make your code
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/// more rusty.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// { let x = ..; x }
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/// ```
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declare_clippy_lint! {
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pub LET_AND_RETURN,
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style,
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"creating a let-binding and then immediately returning it like `let x = expr; x` at \
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the end of a block"
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}
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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: &EarlyContext, block: &ast::Block) {
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if let Some(stmt) = block.stmts.last() {
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match stmt.node {
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ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => {
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self.check_final_expr(cx, expr, Some(stmt.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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// Check a the final expression in a block if it's a return.
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fn check_final_expr(&mut self, cx: &EarlyContext, expr: &ast::Expr, span: Option<Span>) {
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match expr.node {
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// simple return is always "bad"
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ast::ExprKind::Ret(Some(ref inner)) => {
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// allow `#[cfg(a)] return a; #[cfg(b)] return b;`
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if !expr.attrs.iter().any(attr_is_cfg) {
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self.emit_return_lint(cx, span.expect("`else return` is not possible"), inner.span);
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}
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},
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// a whole block? check it!
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ast::ExprKind::Block(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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ast::ExprKind::If(_, 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, None);
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},
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// a match expr, check all arms
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ast::ExprKind::Match(_, ref arms) => for arm in arms {
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self.check_final_expr(cx, &arm.body, Some(arm.body.span));
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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: &EarlyContext, ret_span: Span, inner_span: Span) {
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if in_external_macro(cx, inner_span) || in_macro(inner_span) {
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return;
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}
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span_lint_and_then(cx, NEEDLESS_RETURN, ret_span, "unneeded return statement", |db| {
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if let Some(snippet) = snippet_opt(cx, inner_span) {
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db.span_suggestion(ret_span, "remove `return` as shown", snippet);
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}
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});
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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: &EarlyContext, block: &ast::Block) {
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let mut it = block.stmts.iter();
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// we need both a let-binding stmt and an expr
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if_chain! {
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if let Some(retexpr) = it.next_back();
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if let ast::StmtKind::Expr(ref retexpr) = retexpr.node;
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if let Some(stmt) = it.next_back();
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if let ast::StmtKind::Local(ref local) = stmt.node;
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// don't lint in the presence of type inference
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if local.ty.is_none();
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if !local.attrs.iter().any(attr_is_cfg);
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if let Some(ref initexpr) = local.init;
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if let ast::PatKind::Ident(_, ident, _) = local.pat.node;
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if let ast::ExprKind::Path(_, ref path) = retexpr.node;
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if match_path_ast(path, &[&ident.name.as_str()]);
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if !in_external_macro(cx, initexpr.span);
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then {
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span_note_and_lint(cx,
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LET_AND_RETURN,
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retexpr.span,
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"returning the result of a let binding from a block. \
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Consider returning the expression directly.",
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initexpr.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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}
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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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}
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impl EarlyLintPass for ReturnPass {
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fn check_fn(&mut self, cx: &EarlyContext, kind: FnKind, _: &ast::FnDecl, _: Span, _: ast::NodeId) {
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match kind {
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FnKind::ItemFn(.., block) | FnKind::Method(.., block) => self.check_block_return(cx, block),
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FnKind::Closure(body) => self.check_final_expr(cx, body, Some(body.span)),
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}
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}
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fn check_block(&mut self, cx: &EarlyContext, block: &ast::Block) {
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self.check_let_return(cx, block);
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}
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}
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fn attr_is_cfg(attr: &ast::Attribute) -> bool {
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attr.meta_item_list().is_some() && attr.name().map_or(false, |n| n == "cfg")
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}
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