rust-clippy/clippy_lints/src/blocks_in_if_conditions.rs

144 lines
5.7 KiB
Rust

use crate::utils::{differing_macro_contexts, higher, snippet_block_with_applicability, span_lint, span_lint_and_sugg};
use rustc_errors::Applicability;
use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc_hir::{BlockCheckMode, Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::hir::map::Map;
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:** Checks for `if` conditions that use blocks containing an
/// expression, statements or conditions that use closures with blocks.
///
/// **Why is this bad?** Style, using blocks in the condition makes it hard to read.
///
/// **Known problems:** None.
///
/// **Examples:**
/// ```rust
/// // Bad
/// if { true } { /* ... */ }
///
/// // Good
/// if true { /* ... */ }
/// ```
///
/// // or
///
/// ```rust
/// # fn somefunc() -> bool { true };
/// // Bad
/// if { let x = somefunc(); x } { /* ... */ }
///
/// // Good
/// let res = { let x = somefunc(); x };
/// if res { /* ... */ }
/// ```
pub BLOCKS_IN_IF_CONDITIONS,
style,
"useless or complex blocks that can be eliminated in conditions"
}
declare_lint_pass!(BlocksInIfConditions => [BLOCKS_IN_IF_CONDITIONS]);
struct ExVisitor<'a, 'tcx> {
found_block: Option<&'tcx Expr<'tcx>>,
cx: &'a LateContext<'tcx>,
}
impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
type Map = Map<'tcx>;
fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
if let ExprKind::Closure(_, _, eid, _, _) = expr.kind {
let body = self.cx.tcx.hir().body(eid);
let ex = &body.value;
if matches!(ex.kind, ExprKind::Block(_, _)) && !body.value.span.from_expansion() {
self.found_block = Some(ex);
return;
}
}
walk_expr(self, expr);
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
}
const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
instead, move the block or closure higher and bind it with a `let`";
impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if in_external_macro(cx.sess(), expr.span) {
return;
}
if let Some((cond, _, _)) = higher::if_block(&expr) {
if let ExprKind::Block(block, _) = &cond.kind {
if block.rules == BlockCheckMode::DefaultBlock {
if block.stmts.is_empty() {
if let Some(ex) = &block.expr {
// don't dig into the expression here, just suggest that they remove
// the block
if expr.span.from_expansion() || differing_macro_contexts(expr.span, ex.span) {
return;
}
let mut applicability = Applicability::MachineApplicable;
span_lint_and_sugg(
cx,
BLOCKS_IN_IF_CONDITIONS,
cond.span,
BRACED_EXPR_MESSAGE,
"try",
format!(
"{}",
snippet_block_with_applicability(
cx,
ex.span,
"..",
Some(expr.span),
&mut applicability
)
),
applicability,
);
}
} else {
let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
if span.from_expansion() || differing_macro_contexts(expr.span, span) {
return;
}
// move block higher
let mut applicability = Applicability::MachineApplicable;
span_lint_and_sugg(
cx,
BLOCKS_IN_IF_CONDITIONS,
expr.span.with_hi(cond.span.hi()),
COMPLEX_BLOCK_MESSAGE,
"try",
format!(
"let res = {}; if res",
snippet_block_with_applicability(
cx,
block.span,
"..",
Some(expr.span),
&mut applicability
),
),
applicability,
);
}
}
} else {
let mut visitor = ExVisitor { found_block: None, cx };
walk_expr(&mut visitor, cond);
if let Some(block) = visitor.found_block {
span_lint(cx, BLOCKS_IN_IF_CONDITIONS, block.span, COMPLEX_BLOCK_MESSAGE);
}
}
}
}
}