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_def_path, span_help_and_lint, snippet};
use if_chain::if_chain;
use rustc::hir::*;
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::{declare_lint_pass, declare_tool_lint};
use syntax::ast::LitKind;
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use std::borrow::Cow;
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 {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
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let lint_assert_cb = |is_debug_assert: bool| {
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if let ExprKind::Unary(_, ref lit) = e.kind {
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if let Some((Constant::Bool(is_true), _)) = constant(cx, cx.tables, lit) {
if is_true {
span_help_and_lint(
cx,
ASSERTIONS_ON_CONSTANTS,
e.span,
"`assert!(true)` will be optimized out by the compiler",
"remove it",
);
} else if !is_debug_assert {
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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};
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;
}
lint_assert_cb(true);
} 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;
}
if let Some((panic_message, is_true)) = assert_with_message(&cx, e) {
if is_true {
span_help_and_lint(
cx,
ASSERTIONS_ON_CONSTANTS,
e.span,
"`assert!(true)` will be optimized out by the compiler",
"remove it",
);
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} else if panic_message.is_empty() || panic_message.starts_with("\"assertion failed: ") {
span_help_and_lint(
cx,
ASSERTIONS_ON_CONSTANTS,
e.span,
"`assert!(false)` should probably be replaced",
"use `panic!()` or `unreachable!()`",
);
} else {
span_help_and_lint(
cx,
ASSERTIONS_ON_CONSTANTS,
e.span,
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&format!("`assert!(false, {})` should probably be replaced", panic_message,),
&format!(
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"use `panic!({})` or `unreachable!({})`",
panic_message, panic_message,
),
);
}
}
}
}
}
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/// Check if the expression matches
///
/// ```rust,ignore
/// match { let _t = !c; _t } {
/// true => {
/// {
/// ::std::rt::begin_panic(message, _)
/// }
/// }
/// _ => { }
/// };
/// ```
///
/// where `message` is a string literal and `c` is a constant bool.
///
/// TODO extend this to match anything as message not just string literals
///
/// Returns the `message` argument of `begin_panic` and the value of `c` which is the
/// first argument of `assert!`.
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fn assert_with_message<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> Option<(Cow<'a, str>, bool)> {
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;
if block.stmts.len() == 0;
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);
if args.len() == 2;
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// bind the second argument of the `assert!` macro
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let panic_message_arg = snippet(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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return Some((panic_message_arg, is_true));
}
}
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None
}
/// Matches a function call with the given path and returns the arguments.
///
/// Usage:
///
/// ```rust,ignore
/// if let Some(args) = match_function_call(cx, begin_panic_call, &paths::BEGIN_PANIC);
/// ```
fn match_function_call<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, path: &[&str]) -> Option<&'a [Expr]> {
if_chain! {
if let ExprKind::Call(ref fun, ref args) = expr.kind;
if let ExprKind::Path(ref qpath) = fun.kind;
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if let Some(fun_def_id) = cx.tables.qpath_res(qpath, fun.hir_id).opt_def_id();
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if match_def_path(cx, fun_def_id, path);
then {
return Some(&args)
}
};
None
}