91 lines
3.4 KiB
Rust
91 lines
3.4 KiB
Rust
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use crate::utils::{higher, in_macro, span_lint_and_sugg};
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use if_chain::if_chain;
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use rustc_ast::ast::LitKind;
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use rustc_errors::Applicability;
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use rustc_hir::{BinOpKind, Expr, ExprKind, QPath, StmtKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// **What it does:** Checks for implicit saturating subtraction.
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///
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/// **Why is this bad?** Simplicity and readability. Instead we can easily use an inbuilt function.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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///
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/// ```rust
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/// let end = 10;
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/// let start = 5;
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///
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/// let mut i = end - start;
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///
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/// // Bad
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/// if i != 0 {
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/// i -= 1;
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/// }
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/// ```
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/// Use instead:
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/// ```rust
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/// let end = 10;
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/// let start = 5;
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///
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/// let mut i = end - start;
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///
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/// // Good
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/// i.saturating_sub(1);
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/// ```
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pub IMPLICIT_SATURATING_SUB,
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pedantic,
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"Perform saturating subtraction instead of implicitly checking lower bound of data type"
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}
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declare_lint_pass!(ImplicitSaturatingSub => [IMPLICIT_SATURATING_SUB]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitSaturatingSub {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'tcx>) {
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if in_macro(expr.span) {
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return;
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}
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if_chain! {
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if let Some((ref cond, ref then, None)) = higher::if_block(&expr);
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// Check if the conditional expression is a binary operation
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if let ExprKind::Binary(ref op, ref left, ref right) = cond.kind;
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// Ensure that the binary operator is > or !=
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if BinOpKind::Ne == op.node || BinOpKind::Gt == op.node;
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if let ExprKind::Path(ref cond_path) = left.kind;
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// Get the literal on the right hand side
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if let ExprKind::Lit(ref lit) = right.kind;
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if let LitKind::Int(0, _) = lit.node;
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// Check if the true condition block has only one statement
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if let ExprKind::Block(ref block, _) = then.kind;
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if block.stmts.len() == 1;
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// Check if assign operation is done
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if let StmtKind::Semi(ref e) = block.stmts[0].kind;
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if let ExprKind::AssignOp(ref op1, ref target, ref value) = e.kind;
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if BinOpKind::Sub == op1.node;
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if let ExprKind::Path(ref assign_path) = target.kind;
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// Check if the variable in the condition and assignment statement are the same
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if let (QPath::Resolved(_, ref cres_path), QPath::Resolved(_, ref ares_path)) = (cond_path, assign_path);
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if cres_path.res == ares_path.res;
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if let ExprKind::Lit(ref lit1) = value.kind;
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if let LitKind::Int(assign_lit, _) = lit1.node;
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then {
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// Get the variable name
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let var_name = ares_path.segments[0].ident.name.as_str();
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let applicability = Applicability::MaybeIncorrect;
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span_lint_and_sugg(
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cx,
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IMPLICIT_SATURATING_SUB,
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expr.span,
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"Implicitly performing saturating subtraction",
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"try",
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format!("{}.saturating_sub({});", var_name, assign_lit.to_string()),
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applicability
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);
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}
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}
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}
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}
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