Add lint for debug_assert_with_mut_call

This lint will complain when you put a mutable function/method call
inside a `debug_assert` macro, because it will not be executed in
release mode, therefore it will change the execution flow, which is not
wanted.

1 files changed, 155 insertions, 0 deletions

diff --git a/clippy_lints/src/mutable_debug_assertion.rs b/clippy_lints/src/mutable_debug_assertion.rs
new file mode 100644
index 00000000000..1184db0587b
--- /dev/null
+++ b/clippy_lints/src/mutable_debug_assertion.rs
@@ -0,0 +1,155 @@
+use crate::utils::{is_direct_expn_of, span_lint};
+use if_chain::if_chain;
+use matches::matches;
+use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
+use rustc::hir::{Expr, ExprKind, Mutability, StmtKind, UnOp};
+use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
+use rustc::{declare_lint_pass, declare_tool_lint, ty};
+use syntax_pos::Span;
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for function/method calls with a mutable
+    /// parameter in `debug_assert!`, `debug_assert_eq!` and `debug_assert_ne!` macros.
+    ///
+    /// **Why is this bad?** In release builds `debug_assert!` macros are optimized out by the
+    /// compiler.
+    /// Therefore mutating something in a `debug_assert!` macro results in different behaviour
+    /// between a release and debug build.
+    ///
+    /// **Known problems:** None
+    ///
+    /// **Example:**
+    /// ```rust,ignore
+    /// debug_assert_eq!(vec![3].pop(), Some(3));
+    /// // or
+    /// fn take_a_mut_parameter(_: &mut u32) -> bool { unimplemented!() }
+    /// debug_assert!(take_a_mut_parameter(&mut 5));
+    /// ```
+    pub DEBUG_ASSERT_WITH_MUT_CALL,
+    correctness,
+    "mutable arguments in `debug_assert{,_ne,_eq}!`"
+}
+
+declare_lint_pass!(DebugAssertWithMutCall => [DEBUG_ASSERT_WITH_MUT_CALL]);
+
+const DEBUG_MACRO_NAMES: [&str; 3] = ["debug_assert", "debug_assert_eq", "debug_assert_ne"];
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DebugAssertWithMutCall {
+    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
+        for dmn in &DEBUG_MACRO_NAMES {
+            if is_direct_expn_of(e.span, dmn).is_some() {
+                if let Some(span) = extract_call(cx, e) {
+                    span_lint(
+                        cx,
+                        DEBUG_ASSERT_WITH_MUT_CALL,
+                        span,
+                        &format!("do not call a function with mutable arguments inside of `{}!`", dmn),
+                    );
+                }
+            }
+        }
+    }
+}
+
+//HACK(hellow554): remove this when #4694 is implemented
+#[allow(clippy::cognitive_complexity)]
+fn extract_call<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, e: &'tcx Expr) -> Option<Span> {
+    if_chain! {
+        if let ExprKind::Block(ref block, _) = e.kind;
+        if block.stmts.len() == 1;
+        if let StmtKind::Semi(ref matchexpr) = block.stmts[0].kind;
+        then {
+            if_chain! {
+                if let ExprKind::Match(ref ifclause, _, _) = matchexpr.kind;
+                if let ExprKind::DropTemps(ref droptmp) = ifclause.kind;
+                if let ExprKind::Unary(UnOp::UnNot, ref condition) = droptmp.kind;
+                then {
+                    // debug_assert
+                    let mut visitor = MutArgVisitor::new(cx);
+                    visitor.visit_expr(condition);
+                    return visitor.expr_span();
+                } else {
+                    // debug_assert_{eq,ne}
+                    if_chain! {
+                        if let ExprKind::Block(ref matchblock, _) = matchexpr.kind;
+                        if let Some(ref matchheader) = matchblock.expr;
+                        if let ExprKind::Match(ref headerexpr, _, _) = matchheader.kind;
+                        if let ExprKind::Tup(ref conditions) = headerexpr.kind;
+                        if conditions.len() == 2;
+                        then {
+                            if let ExprKind::AddrOf(_, ref lhs) = conditions[0].kind {
+                                let mut visitor = MutArgVisitor::new(cx);
+                                visitor.visit_expr(lhs);
+                                if let Some(span) = visitor.expr_span() {
+                                    return Some(span);
+                                }
+                            }
+                            if let ExprKind::AddrOf(_, ref rhs) = conditions[1].kind {
+                                let mut visitor = MutArgVisitor::new(cx);
+                                visitor.visit_expr(rhs);
+                                if let Some(span) = visitor.expr_span() {
+                                    return Some(span);
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    None
+}
+
+struct MutArgVisitor<'a, 'tcx> {
+    cx: &'a LateContext<'a, 'tcx>,
+    expr_span: Option<Span>,
+    found: bool,
+}
+
+impl<'a, 'tcx> MutArgVisitor<'a, 'tcx> {
+    fn new(cx: &'a LateContext<'a, 'tcx>) -> Self {
+        Self {
+            cx,
+            expr_span: None,
+            found: false,
+        }
+    }
+
+    fn expr_span(&self) -> Option<Span> {
+        if self.found {
+            self.expr_span
+        } else {
+            None
+        }
+    }
+}
+
+impl<'a, 'tcx> Visitor<'tcx> for MutArgVisitor<'a, 'tcx> {
+    fn visit_expr(&mut self, expr: &'tcx Expr) {
+        match expr.kind {
+            ExprKind::AddrOf(Mutability::MutMutable, _) => {
+                self.found = true;
+                return;
+            },
+            ExprKind::Path(_) => {
+                if let Some(adj) = self.cx.tables.adjustments().get(expr.hir_id) {
+                    if adj
+                        .iter()
+                        .any(|a| matches!(a.target.kind, ty::Ref(_, _, Mutability::MutMutable)))
+                    {
+                        self.found = true;
+                        return;
+                    }
+                }
+            },
+            _ if !self.found => self.expr_span = Some(expr.span),
+            _ => return,
+        }
+        walk_expr(self, expr)
+    }
+
+    fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
+        NestedVisitorMap::OnlyBodies(&self.cx.tcx.hir())
+    }
+}