2021-03-25 18:29:11 +00:00
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use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::source::snippet;
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2021-06-07 00:01:14 +00:00
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use clippy_utils::{path_to_local_id, visitors::is_local_used};
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2018-11-27 20:14:15 +00:00
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use if_chain::if_chain;
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2018-12-29 15:04:45 +00:00
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use rustc_errors::Applicability;
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2020-01-06 16:39:50 +00:00
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use rustc_hir as hir;
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use rustc_hir::BindingAnnotation;
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2020-01-12 06:08:41 +00:00
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use rustc_lint::{LateContext, LateLintPass};
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2020-01-11 11:37:08 +00:00
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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2016-03-30 17:53:43 +00:00
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2018-03-28 13:24:26 +00:00
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declare_clippy_lint! {
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2021-07-29 10:16:06 +00:00
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/// ### What it does
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/// Checks for variable declarations immediately followed by a
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2019-03-05 16:50:33 +00:00
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/// conditional affectation.
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///
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2021-07-29 10:16:06 +00:00
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/// ### Why is this bad?
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/// This is not idiomatic Rust.
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2019-03-05 16:50:33 +00:00
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///
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2021-07-29 10:16:06 +00:00
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/// ### Example
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2019-03-05 16:50:33 +00:00
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/// ```rust,ignore
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/// let foo;
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///
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/// if bar() {
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/// foo = 42;
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/// } else {
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/// foo = 0;
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/// }
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///
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/// let mut baz = None;
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///
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/// if bar() {
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/// baz = Some(42);
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/// }
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/// ```
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///
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/// should be written
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///
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/// ```rust,ignore
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/// let foo = if bar() {
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/// 42
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/// } else {
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/// 0
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/// };
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///
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/// let baz = if bar() {
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/// Some(42)
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/// } else {
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/// None
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/// };
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/// ```
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2016-03-30 17:53:43 +00:00
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pub USELESS_LET_IF_SEQ,
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2020-05-17 15:36:26 +00:00
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nursery,
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2016-08-06 08:18:36 +00:00
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"unidiomatic `let mut` declaration followed by initialization in `if`"
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2016-03-30 17:53:43 +00:00
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}
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2019-04-08 20:43:55 +00:00
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declare_lint_pass!(LetIfSeq => [USELESS_LET_IF_SEQ]);
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2016-03-30 17:53:43 +00:00
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2020-06-25 20:41:36 +00:00
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impl<'tcx> LateLintPass<'tcx> for LetIfSeq {
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fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
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2016-03-30 17:53:43 +00:00
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let mut it = block.stmts.iter().peekable();
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2016-08-01 14:59:14 +00:00
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while let Some(stmt) = it.next() {
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2017-10-23 19:18:02 +00:00
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if_chain! {
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if let Some(expr) = it.peek();
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2021-04-08 15:50:13 +00:00
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if let hir::StmtKind::Local(local) = stmt.kind;
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2019-09-27 15:16:06 +00:00
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if let hir::PatKind::Binding(mode, canonical_id, ident, None) = local.pat.kind;
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2021-04-08 15:50:13 +00:00
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if let hir::StmtKind::Expr(if_) = expr.kind;
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2021-08-08 14:49:13 +00:00
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if let hir::ExprKind::If(hir::Expr { kind: hir::ExprKind::DropTemps(cond), ..}, then, else_) = if_.kind;
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2021-09-02 11:38:17 +00:00
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if !is_local_used(cx, *cond, canonical_id);
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2021-04-08 15:50:13 +00:00
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if let hir::ExprKind::Block(then, _) = then.kind;
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2017-10-23 19:18:02 +00:00
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if let Some(value) = check_assign(cx, canonical_id, &*then);
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2021-06-07 00:01:14 +00:00
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if !is_local_used(cx, value, canonical_id);
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2017-10-23 19:18:02 +00:00
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then {
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let span = stmt.span.to(if_.span);
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2017-11-04 19:55:56 +00:00
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2020-07-17 08:47:04 +00:00
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let has_interior_mutability = !cx.typeck_results().node_type(canonical_id).is_freeze(
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2020-06-21 09:20:48 +00:00
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cx.tcx.at(span),
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2019-04-26 02:07:01 +00:00
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cx.param_env,
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);
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if has_interior_mutability { return; }
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2021-08-08 14:49:13 +00:00
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let (default_multi_stmts, default) = if let Some(else_) = else_ {
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2021-04-08 15:50:13 +00:00
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if let hir::ExprKind::Block(else_, _) = else_.kind {
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2017-10-23 19:18:02 +00:00
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if let Some(default) = check_assign(cx, canonical_id, else_) {
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(else_.stmts.len() > 1, default)
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2021-04-08 15:50:13 +00:00
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} else if let Some(default) = local.init {
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(true, default)
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2017-10-23 19:18:02 +00:00
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} else {
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continue;
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}
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2016-03-30 17:53:43 +00:00
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} else {
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continue;
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}
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2021-04-08 15:50:13 +00:00
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} else if let Some(default) = local.init {
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(false, default)
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2016-03-30 17:53:43 +00:00
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} else {
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continue;
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2017-10-23 19:18:02 +00:00
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};
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2017-11-04 19:55:56 +00:00
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2017-10-23 19:18:02 +00:00
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let mutability = match mode {
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BindingAnnotation::RefMut | BindingAnnotation::Mutable => "<mut> ",
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_ => "",
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};
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2017-11-04 19:55:56 +00:00
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2017-10-23 19:18:02 +00:00
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// FIXME: this should not suggest `mut` if we can detect that the variable is not
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// use mutably after the `if`
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2017-11-04 19:55:56 +00:00
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2017-10-23 19:18:02 +00:00
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let sug = format!(
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"let {mut}{name} = if {cond} {{{then} {value} }} else {{{else} {default} }};",
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mut=mutability,
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2018-06-28 13:46:58 +00:00
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name=ident.name,
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2017-10-23 19:18:02 +00:00
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cond=snippet(cx, cond.span, "_"),
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then=if then.stmts.len() > 1 { " ..;" } else { "" },
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else=if default_multi_stmts { " ..;" } else { "" },
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value=snippet(cx, value.span, "<value>"),
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default=snippet(cx, default.span, "<default>"),
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);
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span_lint_and_then(cx,
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USELESS_LET_IF_SEQ,
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span,
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"`if _ { .. } else { .. }` is an expression",
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2020-04-17 06:08:00 +00:00
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|diag| {
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diag.span_suggestion(
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2018-09-18 15:07:54 +00:00
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span,
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"it is more idiomatic to write",
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sug,
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2018-09-18 19:43:52 +00:00
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Applicability::HasPlaceholders,
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2018-09-18 15:07:54 +00:00
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);
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2017-10-23 19:18:02 +00:00
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if !mutability.is_empty() {
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2020-04-17 06:08:00 +00:00
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diag.note("you might not need `mut` at all");
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2017-10-23 19:18:02 +00:00
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}
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});
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}
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}
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2016-03-30 17:53:43 +00:00
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}
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}
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}
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2020-06-25 20:41:36 +00:00
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fn check_assign<'tcx>(
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cx: &LateContext<'tcx>,
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2019-03-07 20:51:05 +00:00
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decl: hir::HirId,
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2019-12-27 07:12:26 +00:00
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block: &'tcx hir::Block<'_>,
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) -> Option<&'tcx hir::Expr<'tcx>> {
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2017-10-23 19:18:02 +00:00
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if_chain! {
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if block.expr.is_none();
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if let Some(expr) = block.stmts.iter().last();
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2021-04-08 15:50:13 +00:00
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if let hir::StmtKind::Semi(expr) = expr.kind;
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if let hir::ExprKind::Assign(var, value, _) = expr.kind;
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2021-02-11 14:04:38 +00:00
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if path_to_local_id(var, decl);
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2017-10-23 19:18:02 +00:00
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then {
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2021-06-07 00:01:14 +00:00
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if block.stmts.iter().take(block.stmts.len()-1).any(|stmt| is_local_used(cx, stmt, decl)) {
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None
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} else {
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Some(value)
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2016-06-03 17:35:39 +00:00
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}
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2021-06-07 00:01:14 +00:00
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} else {
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None
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2016-03-30 17:53:43 +00:00
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}
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2017-10-23 19:18:02 +00:00
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}
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2016-03-30 17:53:43 +00:00
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}
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