Implement new unused_unsafe-checking algorithm

Author: steffahn

compiler/rustc_middle/src/mir/query.rs

@@ -2,7 +2,7 @@
 
 use crate::mir::{Body, Promoted};
 use crate::ty::{self, Ty, TyCtxt};
-use rustc_data_structures::sync::Lrc;
+use rustc_data_structures::stable_map::FxHashMap;
 use rustc_data_structures::vec_map::VecMap;
 use rustc_errors::ErrorReported;
 use rustc_hir as hir;
@@ -114,13 +114,32 @@ pub struct UnsafetyViolation {
     pub details: UnsafetyViolationDetails,
 }
 
-#[derive(Clone, TyEncodable, TyDecodable, HashStable, Debug)]
+#[derive(Copy, Clone, PartialEq, TyEncodable, TyDecodable, HashStable, Debug)]
+pub enum UnusedUnsafe {
+    /// `unsafe` block contains no unsafe operations
+    // > ``unnecessary `unsafe` block``
+    Unused,
+    // `unsafe` block nested under another (used) `unsafe` block
+    // ``… because it's nested under this `unsafe` block``
+    InUnsafeBlock(hir::HirId),
+    // `unsafe` block nested under `unsafe` fn
+    // ``… because it's nested under this `unsafe` fn``
+    InUnsafeFn(hir::HirId),
+}
+
+#[derive(TyEncodable, TyDecodable, HashStable, Debug)]
 pub struct UnsafetyCheckResult {
     /// Violations that are propagated *upwards* from this function.
-    pub violations: Lrc<[UnsafetyViolation]>,
-    /// `unsafe` blocks in this function, along with whether they are used. This is
-    /// used for the "unused_unsafe" lint.
-    pub unsafe_blocks: Lrc<[(hir::HirId, bool)]>,
+    pub violations: Vec<UnsafetyViolation>,
+
+    /// Used `unsafe` blocks in this function. This is used for the "unused_unsafe" lint.
+    ///
+    /// The keys are the used `unsafe` blocks, the boolean flag indicates whether
+    /// or not any of the usages happen at a place that doesn't allow `unsafe_op_in_unsafe_fn`.
+    pub used_unsafe_blocks: FxHashMap<hir::HirId, bool>,
+
+    /// This is `Some` iff the item is not a closure.
+    pub unused_unsafe: Option<Vec<(hir::HirId, UnusedUnsafe)>>,
 }
 
 rustc_index::newtype_index! {

compiler/rustc_mir_build/src/build/block.rs

@@ -3,8 +3,6 @@ use crate::build::ForGuard::OutsideGuard;
 use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
 use rustc_middle::mir::*;
 use rustc_middle::thir::*;
-use rustc_session::lint::builtin::UNSAFE_OP_IN_UNSAFE_FN;
-use rustc_session::lint::Level;
 use rustc_span::Span;
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {