122 lines
4.7 KiB
Rust
122 lines
4.7 KiB
Rust
use rustc::lint::{LateLintPass, LateContext, LintArray, LintPass};
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use rustc::hir::*;
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use rustc::hir::intravisit::{Visitor, walk_expr, NestedVisitorMap};
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use utils::*;
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/// **What it does:** Checks for `if` conditions that use blocks to contain an
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/// expression.
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///
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/// **Why is this bad?** It isn't really Rust style, same as using parentheses
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/// to contain expressions.
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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 { true } ..
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/// ```
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declare_lint! {
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pub BLOCK_IN_IF_CONDITION_EXPR,
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Warn,
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"braces that can be eliminated in conditions, e.g `if { true } ...`"
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}
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/// **What it does:** Checks for `if` conditions that use blocks containing
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/// statements, or conditions that use closures with blocks.
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///
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/// **Why is this bad?** Using blocks in the condition makes it hard to read.
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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 { let x = somefunc(); x } ..
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/// // or
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/// if somefunc(|x| { x == 47 }) ..
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/// ```
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declare_lint! {
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pub BLOCK_IN_IF_CONDITION_STMT,
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Warn,
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"complex blocks in conditions, e.g. `if { let x = true; x } ...`"
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}
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#[derive(Copy,Clone)]
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pub struct BlockInIfCondition;
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impl LintPass for BlockInIfCondition {
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fn get_lints(&self) -> LintArray {
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lint_array!(BLOCK_IN_IF_CONDITION_EXPR, BLOCK_IN_IF_CONDITION_STMT)
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}
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}
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struct ExVisitor<'a, 'tcx: 'a> {
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found_block: Option<&'tcx Expr>,
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cx: &'a LateContext<'a, 'tcx>,
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}
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impl<'a, 'tcx: 'a> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
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fn visit_expr(&mut self, expr: &'tcx Expr) {
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if let ExprClosure(_, _, eid, _) = expr.node {
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let expr = self.cx.tcx.map.expr(eid);
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if matches!(expr.node, ExprBlock(_)) {
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self.found_block = Some(expr);
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return;
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}
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}
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walk_expr(self, expr);
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}
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fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
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NestedVisitorMap::All(&self.cx.tcx.map)
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}
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}
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const BRACED_EXPR_MESSAGE: &'static str = "omit braces around single expression condition";
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const COMPLEX_BLOCK_MESSAGE: &'static str = "in an 'if' condition, avoid complex blocks or closures with blocks; \
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instead, move the block or closure higher and bind it with a 'let'";
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impl LateLintPass for BlockInIfCondition {
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fn check_expr<'a, 'tcx: 'a>(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if let ExprIf(ref check, ref then, _) = expr.node {
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if let ExprBlock(ref block) = check.node {
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if block.rules == DefaultBlock {
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if block.stmts.is_empty() {
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if let Some(ref ex) = block.expr {
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// don't dig into the expression here, just suggest that they remove
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// the block
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if in_macro(cx, expr.span) || differing_macro_contexts(expr.span, ex.span) {
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return;
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}
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span_help_and_lint(cx,
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BLOCK_IN_IF_CONDITION_EXPR,
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check.span,
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BRACED_EXPR_MESSAGE,
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&format!("try\nif {} {} ... ",
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snippet_block(cx, ex.span, ".."),
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snippet_block(cx, then.span, "..")));
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}
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} else {
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let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
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if in_macro(cx, span) || differing_macro_contexts(expr.span, span) {
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return;
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}
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// move block higher
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span_help_and_lint(cx,
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BLOCK_IN_IF_CONDITION_STMT,
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check.span,
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COMPLEX_BLOCK_MESSAGE,
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&format!("try\nlet res = {};\nif res {} ... ",
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snippet_block(cx, block.span, ".."),
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snippet_block(cx, then.span, "..")));
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}
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}
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} else {
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let mut visitor = ExVisitor { found_block: None, cx: cx };
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walk_expr(&mut visitor, check);
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if let Some(block) = visitor.found_block {
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span_lint(cx, BLOCK_IN_IF_CONDITION_STMT, block.span, COMPLEX_BLOCK_MESSAGE);
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}
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}
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}
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}
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}
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