139 lines
4.0 KiB
Rust
139 lines
4.0 KiB
Rust
use rustc::lint::*;
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use rustc::hir::*;
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use rustc::hir::def::Def;
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use utils::sugg::Sugg;
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use syntax::ptr::P;
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use utils::{match_def_path, match_type, span_lint_and_then};
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use utils::paths::*;
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/// **What it does:** Checks for expressions that could be replaced by the question mark operator
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///
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/// **Why is this bad?** Question mark usage is more idiomatic
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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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/// if option.is_none() {
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/// return None;
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/// }
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/// ```
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///
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/// Could be written:
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///
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/// ```rust
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/// option?;
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/// ```
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declare_lint!{
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pub QUESTION_MARK,
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Warn,
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"checks for expressions that could be replaced by the question mark operator"
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}
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#[derive(Copy, Clone)]
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pub struct QuestionMarkPass;
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impl LintPass for QuestionMarkPass {
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fn get_lints(&self) -> LintArray {
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lint_array!(QUESTION_MARK)
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}
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}
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impl QuestionMarkPass {
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/// Check if the given expression on the given context matches the following structure:
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///
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/// ```
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/// if option.is_none() {
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/// return None;
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/// }
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/// ```
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///
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/// If it matches, it will suggest to use the question mark operator instead
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fn check_is_none_and_early_return_none(cx: &LateContext, expr: &Expr) {
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if_chain! {
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if let ExprIf(ref if_expr, ref body, _) = expr.node;
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if let ExprMethodCall(ref segment, _, ref args) = if_expr.node;
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if segment.name == "is_none";
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if Self::expression_returns_none(cx, &body);
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if let Some(subject) = args.get(0);
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if Self::is_option(cx, subject);
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then {
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span_lint_and_then(
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cx,
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QUESTION_MARK,
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expr.span,
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&format!("this block may be rewritten with the `?` operator"),
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|db| {
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let receiver_str = &Sugg::hir(cx, subject, "..");
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db.span_suggestion(
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expr.span,
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"replace_it_with",
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format!("{}?;", receiver_str),
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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 is_option(cx: &LateContext, expression: &Expr) -> bool {
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let expr_ty = cx.tables.expr_ty(expression);
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return match_type(cx, expr_ty, &OPTION);
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}
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fn expression_returns_none(cx: &LateContext, expression: &Expr) -> bool {
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match expression.node {
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ExprBlock(ref block) => {
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if let Some(return_expression) = Self::return_expression(block) {
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return Self::expression_returns_none(cx, &return_expression);
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}
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false
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},
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ExprRet(Some(ref expr)) => {
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Self::expression_returns_none(cx, expr)
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},
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ExprPath(ref qp) => {
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if let Def::VariantCtor(def_id, _) = cx.tables.qpath_def(qp, expression.hir_id) {
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return match_def_path(cx.tcx, def_id, &OPTION_NONE);
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}
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false
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},
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_ => false
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}
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}
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fn return_expression(block: &Block) -> Option<P<Expr>> {
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// Check if last expression is a return statement. Then, return the expression
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if_chain! {
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if block.stmts.len() == 1;
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if let Some(expr) = block.stmts.iter().last();
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if let StmtSemi(ref expr, _) = expr.node;
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if let ExprRet(ref ret_expr) = expr.node;
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if let &Some(ref ret_expr) = ret_expr;
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then {
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return Some(ret_expr.clone());
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}
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}
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// Check if the block has an implicit return expression
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if let Some(ref ret_expr) = block.expr {
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return Some(ret_expr.clone());
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}
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return None;
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for QuestionMarkPass {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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Self::check_is_none_and_early_return_none(cx, expr);
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}
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}
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