237 lines
8.1 KiB
Rust
237 lines
8.1 KiB
Rust
// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Checks for needless boolean results of if-else expressions
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//!
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//! This lint is **warn** by default
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use crate::rustc::hir::*;
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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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use crate::rustc_errors::Applicability;
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use crate::syntax::ast::LitKind;
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use crate::syntax::source_map::Spanned;
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use crate::utils::sugg::Sugg;
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use crate::utils::{in_macro, snippet, span_lint, span_lint_and_sugg};
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/// **What it does:** Checks for expressions of the form `if c { true } else {
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/// false }`
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/// (or vice versa) and suggest using the condition directly.
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///
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/// **Why is this bad?** Redundant code.
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///
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/// **Known problems:** Maybe false positives: Sometimes, the two branches are
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/// painstakingly documented (which we of course do not detect), so they *may*
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/// have some value. Even then, the documentation can be rewritten to match the
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/// shorter code.
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///
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/// **Example:**
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/// ```rust
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/// if x { false } else { true }
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/// ```
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declare_clippy_lint! {
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pub NEEDLESS_BOOL,
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complexity,
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"if-statements with plain booleans in the then- and else-clause, e.g. \
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`if p { true } else { false }`"
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}
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/// **What it does:** Checks for expressions of the form `x == true` (or vice
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/// versa) and suggest using the variable directly.
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///
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/// **Why is this bad?** Unnecessary code.
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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 x == true { } // could be `if x { }`
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/// ```
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declare_clippy_lint! {
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pub BOOL_COMPARISON,
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complexity,
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"comparing a variable to a boolean, e.g. `if x == true`"
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}
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#[derive(Copy, Clone)]
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pub struct NeedlessBool;
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impl LintPass for NeedlessBool {
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fn get_lints(&self) -> LintArray {
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lint_array!(NEEDLESS_BOOL)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBool {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
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use self::Expression::*;
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if let ExprKind::If(ref pred, ref then_block, Some(ref else_expr)) = e.node {
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let reduce = |ret, not| {
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let snip = Sugg::hir(cx, pred, "<predicate>");
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let snip = if not { !snip } else { snip };
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let hint = if ret {
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format!("return {}", snip)
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} else {
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snip.to_string()
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};
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span_lint_and_sugg(
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cx,
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NEEDLESS_BOOL,
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e.span,
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"this if-then-else expression returns a bool literal",
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"you can reduce it to",
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hint,
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Applicability::Unspecified,
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);
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};
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if let ExprKind::Block(ref then_block, _) = then_block.node {
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match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
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(RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
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span_lint(
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cx,
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NEEDLESS_BOOL,
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e.span,
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"this if-then-else expression will always return true",
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);
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},
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(RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
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span_lint(
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cx,
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NEEDLESS_BOOL,
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e.span,
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"this if-then-else expression will always return false",
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);
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},
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(RetBool(true), RetBool(false)) => reduce(true, false),
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(Bool(true), Bool(false)) => reduce(false, false),
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(RetBool(false), RetBool(true)) => reduce(true, true),
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(Bool(false), Bool(true)) => reduce(false, true),
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_ => (),
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}
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} else {
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panic!("IfExpr 'then' node is not an ExprKind::Block");
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}
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}
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}
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}
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#[derive(Copy, Clone)]
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pub struct BoolComparison;
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impl LintPass for BoolComparison {
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fn get_lints(&self) -> LintArray {
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lint_array!(BOOL_COMPARISON)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoolComparison {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
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use self::Expression::*;
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if in_macro(e.span) {
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return;
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}
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if let ExprKind::Binary(Spanned { node: BinOpKind::Eq, .. }, ref left_side, ref right_side) = e.node {
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match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
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(Bool(true), Other) => {
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let hint = snippet(cx, right_side.span, "..").into_owned();
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span_lint_and_sugg(
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cx,
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BOOL_COMPARISON,
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e.span,
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"equality checks against true are unnecessary",
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"try simplifying it as shown",
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hint,
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Applicability::Unspecified,
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);
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},
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(Other, Bool(true)) => {
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let hint = snippet(cx, left_side.span, "..").into_owned();
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span_lint_and_sugg(
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cx,
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BOOL_COMPARISON,
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e.span,
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"equality checks against true are unnecessary",
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"try simplifying it as shown",
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hint,
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Applicability::Unspecified,
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);
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},
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(Bool(false), Other) => {
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let hint = Sugg::hir(cx, right_side, "..");
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span_lint_and_sugg(
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cx,
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BOOL_COMPARISON,
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e.span,
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"equality checks against false can be replaced by a negation",
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"try simplifying it as shown",
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(!hint).to_string(),
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Applicability::Unspecified,
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);
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},
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(Other, Bool(false)) => {
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let hint = Sugg::hir(cx, left_side, "..");
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span_lint_and_sugg(
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cx,
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BOOL_COMPARISON,
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e.span,
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"equality checks against false can be replaced by a negation",
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"try simplifying it as shown",
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(!hint).to_string(),
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Applicability::Unspecified,
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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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}
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enum Expression {
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Bool(bool),
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RetBool(bool),
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Other,
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}
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fn fetch_bool_block(block: &Block) -> Expression {
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match (&*block.stmts, block.expr.as_ref()) {
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(&[], Some(e)) => fetch_bool_expr(&**e),
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(&[ref e], None) => if let StmtKind::Semi(ref e, _) = e.node {
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if let ExprKind::Ret(_) = e.node {
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fetch_bool_expr(&**e)
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} else {
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Expression::Other
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}
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} else {
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Expression::Other
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},
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_ => Expression::Other,
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}
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}
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fn fetch_bool_expr(expr: &Expr) -> Expression {
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match expr.node {
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ExprKind::Block(ref block, _) => fetch_bool_block(block),
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ExprKind::Lit(ref lit_ptr) => if let LitKind::Bool(value) = lit_ptr.node {
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Expression::Bool(value)
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} else {
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Expression::Other
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},
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ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
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Expression::Bool(value) => Expression::RetBool(value),
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_ => Expression::Other,
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},
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_ => Expression::Other,
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}
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}
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