New upstream version 1.52.1+dfsg1

[rustc.git] / src / tools / clippy / clippy_lints / src / loops / while_immutable_condition.rs

diff --git a/src/tools/clippy/clippy_lints/src/loops/while_immutable_condition.rs b/src/tools/clippy/clippy_lints/src/loops/while_immutable_condition.rs
new file mode 100644 (file)
index 0000000..05e0a72
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/loops/while_immutable_condition.rs
@@ -0,0 +1,139 @@
+use super::WHILE_IMMUTABLE_CONDITION;
+use crate::consts::constant;
+use crate::utils::span_lint_and_then;
+use crate::utils::usage::mutated_variables;
+use if_chain::if_chain;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_hir::def::{DefKind, Res};
+use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
+use rustc_hir::{def_id, Expr, ExprKind, HirId, QPath};
+use rustc_lint::LateContext;
+use rustc_middle::hir::map::Map;
+use std::iter::Iterator;
+
+pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
+    if constant(cx, cx.typeck_results(), cond).is_some() {
+        // A pure constant condition (e.g., `while false`) is not linted.
+        return;
+    }
+
+    let mut var_visitor = VarCollectorVisitor {
+        cx,
+        ids: FxHashSet::default(),
+        def_ids: FxHashMap::default(),
+        skip: false,
+    };
+    var_visitor.visit_expr(cond);
+    if var_visitor.skip {
+        return;
+    }
+    let used_in_condition = &var_visitor.ids;
+    let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
+        used_in_condition.is_disjoint(&used_mutably)
+    } else {
+        return;
+    };
+    let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
+
+    let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
+        has_break_or_return: false,
+    };
+    has_break_or_return_visitor.visit_expr(expr);
+    let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
+
+    if no_cond_variable_mutated && !mutable_static_in_cond {
+        span_lint_and_then(
+            cx,
+            WHILE_IMMUTABLE_CONDITION,
+            cond.span,
+            "variables in the condition are not mutated in the loop body",
+            |diag| {
+                diag.note("this may lead to an infinite or to a never running loop");
+
+                if has_break_or_return {
+                    diag.note("this loop contains `return`s or `break`s");
+                    diag.help("rewrite it as `if cond { loop { } }`");
+                }
+            },
+        );
+    }
+}
+
+struct HasBreakOrReturnVisitor {
+    has_break_or_return: bool,
+}
+
+impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
+    type Map = Map<'tcx>;
+
+    fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
+        if self.has_break_or_return {
+            return;
+        }
+
+        match expr.kind {
+            ExprKind::Ret(_) | ExprKind::Break(_, _) => {
+                self.has_break_or_return = true;
+                return;
+            },
+            _ => {},
+        }
+
+        walk_expr(self, expr);
+    }
+
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::None
+    }
+}
+
+/// Collects the set of variables in an expression
+/// Stops analysis if a function call is found
+/// Note: In some cases such as `self`, there are no mutable annotation,
+/// All variables definition IDs are collected
+struct VarCollectorVisitor<'a, 'tcx> {
+    cx: &'a LateContext<'tcx>,
+    ids: FxHashSet<HirId>,
+    def_ids: FxHashMap<def_id::DefId, bool>,
+    skip: bool,
+}
+
+impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
+    fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
+        if_chain! {
+            if let ExprKind::Path(ref qpath) = ex.kind;
+            if let QPath::Resolved(None, _) = *qpath;
+            let res = self.cx.qpath_res(qpath, ex.hir_id);
+            then {
+                match res {
+                    Res::Local(hir_id) => {
+                        self.ids.insert(hir_id);
+                    },
+                    Res::Def(DefKind::Static, def_id) => {
+                        let mutable = self.cx.tcx.is_mutable_static(def_id);
+                        self.def_ids.insert(def_id, mutable);
+                    },
+                    _ => {},
+                }
+            }
+        }
+    }
+}
+
+impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
+    type Map = Map<'tcx>;
+
+    fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
+        match ex.kind {
+            ExprKind::Path(_) => self.insert_def_id(ex),
+            // If there is any function/method call… we just stop analysis
+            ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
+
+            _ => walk_expr(self, ex),
+        }
+    }
+
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::None
+    }
+}