rust/clippy_lints/src/block_in_if_condition.rs
2019-01-27 01:42:34 +01:00

137 lines
4.9 KiB
Rust

use crate::utils::*;
use matches::matches;
use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc::hir::*;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::{declare_tool_lint, lint_array};
/// **What it does:** Checks for `if` conditions that use blocks to contain an
/// expression.
///
/// **Why is this bad?** It isn't really Rust style, same as using parentheses
/// to contain expressions.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// if { true } ..
/// ```
declare_clippy_lint! {
pub BLOCK_IN_IF_CONDITION_EXPR,
style,
"braces that can be eliminated in conditions, e.g. `if { true } ...`"
}
/// **What it does:** Checks for `if` conditions that use blocks containing
/// statements, or conditions that use closures with blocks.
///
/// **Why is this bad?** Using blocks in the condition makes it hard to read.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// if { let x = somefunc(); x } ..
/// // or
/// if somefunc(|x| { x == 47 }) ..
/// ```
declare_clippy_lint! {
pub BLOCK_IN_IF_CONDITION_STMT,
style,
"complex blocks in conditions, e.g. `if { let x = true; x } ...`"
}
#[derive(Copy, Clone)]
pub struct BlockInIfCondition;
impl LintPass for BlockInIfCondition {
fn get_lints(&self) -> LintArray {
lint_array!(BLOCK_IN_IF_CONDITION_EXPR, BLOCK_IN_IF_CONDITION_STMT)
}
fn name(&self) -> &'static str {
"BlockInIfCondition"
}
}
struct ExVisitor<'a, 'tcx: 'a> {
found_block: Option<&'tcx Expr>,
cx: &'a LateContext<'a, 'tcx>,
}
impl<'a, 'tcx: 'a> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr) {
if let ExprKind::Closure(_, _, eid, _, _) = expr.node {
let body = self.cx.tcx.hir().body(eid);
let ex = &body.value;
if matches!(ex.node, ExprKind::Block(_, _)) && !in_macro(body.value.span) {
self.found_block = Some(ex);
return;
}
}
walk_expr(self, expr);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
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<'a, 'tcx> LateLintPass<'a, 'tcx> for BlockInIfCondition {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let ExprKind::If(check, then, _) = &expr.node {
if let ExprKind::Block(block, _) = &check.node {
if block.rules == 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 in_macro(expr.span) || differing_macro_contexts(expr.span, ex.span) {
return;
}
span_help_and_lint(
cx,
BLOCK_IN_IF_CONDITION_EXPR,
check.span,
BRACED_EXPR_MESSAGE,
&format!(
"try\nif {} {} ... ",
snippet_block(cx, ex.span, ".."),
snippet_block(cx, then.span, "..")
),
);
}
} else {
let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
if in_macro(span) || differing_macro_contexts(expr.span, span) {
return;
}
// move block higher
span_help_and_lint(
cx,
BLOCK_IN_IF_CONDITION_STMT,
check.span,
COMPLEX_BLOCK_MESSAGE,
&format!(
"try\nlet res = {};\nif res {} ... ",
snippet_block(cx, block.span, ".."),
snippet_block(cx, then.span, "..")
),
);
}
}
} else {
let mut visitor = ExVisitor { found_block: None, cx };
walk_expr(&mut visitor, check);
if let Some(block) = visitor.found_block {
span_lint(cx, BLOCK_IN_IF_CONDITION_STMT, block.span, COMPLEX_BLOCK_MESSAGE);
}
}
}
}
}