2018-09-16 23:25:33 +00:00
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use crate::rustc::hir::{Expr, ExprKind, MutMutable, QPath};
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use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use crate::rustc::{declare_tool_lint, lint_array};
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2018-09-18 23:54:01 +00:00
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use crate::utils::{match_def_path, match_qpath, opt_def_id, paths, snippet, span_lint_and_sugg};
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2018-09-16 23:25:33 +00:00
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use if_chain::if_chain;
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/// **What it does:** Checks for `mem::replace()` on an `Option` with
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/// `None`.
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///
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/// **Why is this bad?** `Option` already has the method `take()` for
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/// taking its current value (Some(..) or None) and replacing it with
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/// `None`.
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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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2018-09-18 17:21:49 +00:00
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/// let mut an_option = Some(0);
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2018-09-16 23:25:33 +00:00
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/// let replaced = mem::replace(&mut an_option, None);
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/// ```
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/// Is better expressed with:
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/// ```rust
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2018-09-18 17:21:49 +00:00
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/// let mut an_option = Some(0);
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2018-09-16 23:25:33 +00:00
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/// let taken = an_option.take();
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/// ```
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declare_clippy_lint! {
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pub MEM_REPLACE_OPTION_WITH_NONE,
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style,
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"replacing an `Option` with `None` instead of `take()`"
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}
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pub struct MemReplace;
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impl LintPass for MemReplace {
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fn get_lints(&self) -> LintArray {
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lint_array![MEM_REPLACE_OPTION_WITH_NONE]
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemReplace {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if_chain! {
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2018-09-18 23:54:01 +00:00
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// Check that `expr` is a call to `mem::replace()`
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2018-09-16 23:25:33 +00:00
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if let ExprKind::Call(ref func, ref func_args) = expr.node;
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if func_args.len() == 2;
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if let ExprKind::Path(ref func_qpath) = func.node;
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if let Some(def_id) = opt_def_id(cx.tables.qpath_def(func_qpath, func.hir_id));
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if match_def_path(cx.tcx, def_id, &paths::MEM_REPLACE);
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2018-09-18 23:54:01 +00:00
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// Check that second argument is `Option::None`
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2018-09-16 23:25:33 +00:00
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if let ExprKind::Path(ref replacement_qpath) = func_args[1].node;
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if match_qpath(replacement_qpath, &paths::OPTION_NONE);
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2018-09-18 23:54:01 +00:00
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2018-09-16 23:25:33 +00:00
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then {
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2018-09-18 23:54:01 +00:00
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// Since this is a late pass (already type-checked),
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// and we already know that the second argument is an
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2018-09-19 21:54:38 +00:00
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// `Option`, we do not need to check the first
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2018-09-18 23:54:01 +00:00
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// argument's type. All that's left is to get
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// replacee's path.
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let replaced_path = match func_args[0].node {
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ExprKind::AddrOf(MutMutable, ref replaced) => {
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if let ExprKind::Path(QPath::Resolved(None, ref replaced_path)) = replaced.node {
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replaced_path
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} else {
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return
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}
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},
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ExprKind::Path(QPath::Resolved(None, ref replaced_path)) => replaced_path,
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_ => return,
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};
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2018-09-16 23:25:33 +00:00
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span_lint_and_sugg(
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cx,
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MEM_REPLACE_OPTION_WITH_NONE,
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expr.span,
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"replacing an `Option` with `None`",
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"consider `Option::take()` instead",
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2018-09-18 23:54:01 +00:00
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format!("{}.take()", snippet(cx, replaced_path.span, ""))
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2018-09-16 23:25:33 +00:00
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);
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}
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}
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}
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}
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