Update upstream source from tag 'upstream/1.52.1+dfsg1'

[rustc.git] / src / tools / clippy / clippy_lints / src / if_let_mutex.rs

diff --git a/src/tools/clippy/clippy_lints/src/if_let_mutex.rs b/src/tools/clippy/clippy_lints/src/if_let_mutex.rs
new file mode 100644 (file)
index 0000000..58511c6
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/if_let_mutex.rs
@@ -0,0 +1,157 @@
+use crate::utils::{is_type_diagnostic_item, span_lint_and_help, SpanlessEq};
+use if_chain::if_chain;
+use rustc_hir::intravisit::{self as visit, NestedVisitorMap, Visitor};
+use rustc_hir::{Expr, ExprKind, MatchSource};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::hir::map::Map;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for `Mutex::lock` calls in `if let` expression
+    /// with lock calls in any of the else blocks.
+    ///
+    /// **Why is this bad?** The Mutex lock remains held for the whole
+    /// `if let ... else` block and deadlocks.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust,ignore
+    /// if let Ok(thing) = mutex.lock() {
+    ///     do_thing();
+    /// } else {
+    ///     mutex.lock();
+    /// }
+    /// ```
+    /// Should be written
+    /// ```rust,ignore
+    /// let locked = mutex.lock();
+    /// if let Ok(thing) = locked {
+    ///     do_thing(thing);
+    /// } else {
+    ///     use_locked(locked);
+    /// }
+    /// ```
+    pub IF_LET_MUTEX,
+    correctness,
+    "locking a `Mutex` in an `if let` block can cause deadlocks"
+}
+
+declare_lint_pass!(IfLetMutex => [IF_LET_MUTEX]);
+
+impl<'tcx> LateLintPass<'tcx> for IfLetMutex {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, ex: &'tcx Expr<'tcx>) {
+        let mut arm_visit = ArmVisitor {
+            mutex_lock_called: false,
+            found_mutex: None,
+            cx,
+        };
+        let mut op_visit = OppVisitor {
+            mutex_lock_called: false,
+            found_mutex: None,
+            cx,
+        };
+        if let ExprKind::Match(
+            ref op,
+            ref arms,
+            MatchSource::IfLetDesugar {
+                contains_else_clause: true,
+            },
+        ) = ex.kind
+        {
+            op_visit.visit_expr(op);
+            if op_visit.mutex_lock_called {
+                for arm in *arms {
+                    arm_visit.visit_arm(arm);
+                }
+
+                if arm_visit.mutex_lock_called && arm_visit.same_mutex(cx, op_visit.found_mutex.unwrap()) {
+                    span_lint_and_help(
+                        cx,
+                        IF_LET_MUTEX,
+                        ex.span,
+                        "calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a deadlock",
+                        None,
+                        "move the lock call outside of the `if let ...` expression",
+                    );
+                }
+            }
+        }
+    }
+}
+
+/// Checks if `Mutex::lock` is called in the `if let _ = expr.
+pub struct OppVisitor<'a, 'tcx> {
+    mutex_lock_called: bool,
+    found_mutex: Option<&'tcx Expr<'tcx>>,
+    cx: &'a LateContext<'tcx>,
+}
+
+impl<'tcx> Visitor<'tcx> for OppVisitor<'_, 'tcx> {
+    type Map = Map<'tcx>;
+
+    fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
+        if_chain! {
+            if let Some(mutex) = is_mutex_lock_call(self.cx, expr);
+            then {
+                self.found_mutex = Some(mutex);
+                self.mutex_lock_called = true;
+                return;
+            }
+        }
+        visit::walk_expr(self, expr);
+    }
+
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::None
+    }
+}
+
+/// Checks if `Mutex::lock` is called in any of the branches.
+pub struct ArmVisitor<'a, 'tcx> {
+    mutex_lock_called: bool,
+    found_mutex: Option<&'tcx Expr<'tcx>>,
+    cx: &'a LateContext<'tcx>,
+}
+
+impl<'tcx> Visitor<'tcx> for ArmVisitor<'_, 'tcx> {
+    type Map = Map<'tcx>;
+
+    fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
+        if_chain! {
+            if let Some(mutex) = is_mutex_lock_call(self.cx, expr);
+            then {
+                self.found_mutex = Some(mutex);
+                self.mutex_lock_called = true;
+                return;
+            }
+        }
+        visit::walk_expr(self, expr);
+    }
+
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::None
+    }
+}
+
+impl<'tcx, 'l> ArmVisitor<'tcx, 'l> {
+    fn same_mutex(&self, cx: &LateContext<'_>, op_mutex: &Expr<'_>) -> bool {
+        self.found_mutex
+            .map_or(false, |arm_mutex| SpanlessEq::new(cx).eq_expr(op_mutex, arm_mutex))
+    }
+}
+
+fn is_mutex_lock_call<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
+    if_chain! {
+        if let ExprKind::MethodCall(path, _span, args, _) = &expr.kind;
+        if path.ident.as_str() == "lock";
+        let ty = cx.typeck_results().expr_ty(&args[0]);
+        if is_type_diagnostic_item(cx, ty, sym!(mutex_type));
+        then {
+            Some(&args[0])
+        } else {
+            None
+        }
+    }
+}