rust-clippy/clippy_lints/src/assertions_on_constants.rs

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use crate::consts::{constant, Constant};
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use crate::utils::paths;
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use crate::utils::{is_direct_expn_of, is_expn_of, match_function_call, snippet_opt, span_help_and_lint};
use if_chain::if_chain;
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use rustc::declare_lint_pass;
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc_hir::*;
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use rustc_session::declare_tool_lint;
use syntax::ast::LitKind;
declare_clippy_lint! {
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/// **What it does:** Checks for `assert!(true)` and `assert!(false)` calls.
///
/// **Why is this bad?** Will be optimized out by the compiler or should probably be replaced by a
/// panic!() or unreachable!()
///
/// **Known problems:** None
///
/// **Example:**
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/// ```rust,ignore
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/// assert!(false)
/// // or
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/// assert!(true)
/// // or
/// const B: bool = false;
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/// assert!(B)
/// ```
pub ASSERTIONS_ON_CONSTANTS,
style,
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"`assert!(true)` / `assert!(false)` will be optimized out by the compiler, and should probably be replaced by a `panic!()` or `unreachable!()`"
}
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declare_lint_pass!(AssertionsOnConstants => [ASSERTIONS_ON_CONSTANTS]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssertionsOnConstants {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
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let lint_true = || {
span_help_and_lint(
cx,
ASSERTIONS_ON_CONSTANTS,
e.span,
"`assert!(true)` will be optimized out by the compiler",
"remove it",
);
};
let lint_false_without_message = || {
span_help_and_lint(
cx,
ASSERTIONS_ON_CONSTANTS,
e.span,
"`assert!(false)` should probably be replaced",
"use `panic!()` or `unreachable!()`",
);
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};
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let lint_false_with_message = |panic_message: String| {
span_help_and_lint(
cx,
ASSERTIONS_ON_CONSTANTS,
e.span,
&format!("`assert!(false, {})` should probably be replaced", panic_message),
&format!("use `panic!({})` or `unreachable!({})`", panic_message, panic_message),
)
};
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if let Some(debug_assert_span) = is_expn_of(e.span, "debug_assert") {
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if debug_assert_span.from_expansion() {
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return;
}
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if_chain! {
if let ExprKind::Unary(_, ref lit) = e.kind;
if let Some((Constant::Bool(is_true), _)) = constant(cx, cx.tables, lit);
if is_true;
then {
lint_true();
}
};
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} else if let Some(assert_span) = is_direct_expn_of(e.span, "assert") {
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if assert_span.from_expansion() {
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return;
}
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if let Some(assert_match) = match_assert_with_message(&cx, e) {
match assert_match {
// matched assert but not message
AssertKind::WithoutMessage(false) => lint_false_without_message(),
AssertKind::WithoutMessage(true) | AssertKind::WithMessage(_, true) => lint_true(),
AssertKind::WithMessage(panic_message, false) => lint_false_with_message(panic_message),
};
}
}
}
}
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/// Result of calling `match_assert_with_message`.
enum AssertKind {
WithMessage(String, bool),
WithoutMessage(bool),
}
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/// Check if the expression matches
///
/// ```rust,ignore
/// match { let _t = !c; _t } {
/// true => {
/// {
/// ::std::rt::begin_panic(message, _)
/// }
/// }
/// _ => { }
/// };
/// ```
///
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/// where `message` is any expression and `c` is a constant bool.
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fn match_assert_with_message<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) -> Option<AssertKind> {
if_chain! {
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if let ExprKind::Match(ref expr, ref arms, _) = expr.kind;
// matches { let _t = expr; _t }
if let ExprKind::DropTemps(ref expr) = expr.kind;
if let ExprKind::Unary(UnOp::UnNot, ref expr) = expr.kind;
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// bind the first argument of the `assert!` macro
if let Some((Constant::Bool(is_true), _)) = constant(cx, cx.tables, expr);
// arm 1 pattern
if let PatKind::Lit(ref lit_expr) = arms[0].pat.kind;
if let ExprKind::Lit(ref lit) = lit_expr.kind;
if let LitKind::Bool(true) = lit.node;
// arm 1 block
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if let ExprKind::Block(ref block, _) = arms[0].body.kind;
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if block.stmts.is_empty();
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if let Some(block_expr) = &block.expr;
if let ExprKind::Block(ref inner_block, _) = block_expr.kind;
if let Some(begin_panic_call) = &inner_block.expr;
// function call
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if let Some(args) = match_function_call(cx, begin_panic_call, &paths::BEGIN_PANIC);
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if args.len() == 1;
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// bind the second argument of the `assert!` macro if it exists
if let panic_message = snippet_opt(cx, args[0].span);
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// second argument of begin_panic is irrelevant
// as is the second match arm
then {
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// an empty message occurs when it was generated by the macro
// (and not passed by the user)
return panic_message
.filter(|msg| !msg.is_empty())
.map(|msg| AssertKind::WithMessage(msg, is_true))
.or(Some(AssertKind::WithoutMessage(is_true)));
}
}
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None
}