fix undocumented-unsafe-blocks false positive

Author: llogiq

clippy_lints/src/undocumented_unsafe_blocks.rs

@@ -68,7 +68,8 @@ impl LateLintPass<'_> for UndocumentedUnsafeBlocks {
             && !in_external_macro(cx.tcx.sess, block.span)
             && !is_lint_allowed(cx, UNDOCUMENTED_UNSAFE_BLOCKS, block.hir_id)
             && !is_unsafe_from_proc_macro(cx, block.span)
-            && !block_has_safety_comment(cx, block)
+            && !block_has_safety_comment(cx, block.span)
+            && !block_parents_have_safety_comment(cx, block.hir_id)
         {
             let source_map = cx.tcx.sess.source_map();
             let span = if source_map.is_multiline(block.span) {
@@ -126,8 +127,51 @@ fn is_unsafe_from_proc_macro(cx: &LateContext<'_>, span: Span) -> bool {
         .map_or(true, |src| !src.starts_with("unsafe"))
 }
 
+// Checks if any parent {expression, statement, block, local, const, static}
+// has a safety comment
+fn block_parents_have_safety_comment(cx: &LateContext<'_>, id: hir::HirId) -> bool {
+    for (_, node) in cx.tcx.hir().parent_iter(id) {
+        match node {
+            Node::Expr(expr) => {
+                if !is_branchy(expr) && span_in_body_has_safety_comment(cx, expr.span) {
+                    return true;
+                }
+            },
+            Node::Stmt(hir::Stmt {
+                kind:
+                    hir::StmtKind::Local(hir::Local { span, .. })
+                    | hir::StmtKind::Expr(hir::Expr { span, .. })
+                    | hir::StmtKind::Semi(hir::Expr { span, .. }),
+                ..
+            })
+            | Node::Local(hir::Local { span, .. })
+            | Node::Item(hir::Item {
+                kind: hir::ItemKind::Const(..) | ItemKind::Static(..),
+                span,
+                ..
+            }) => {
+                if span_in_body_has_safety_comment(cx, *span) {
+                    return true;
+                }
+            },
+            _ => {
+                break;
+            },
+        }
+    }
+    false
+}
+
+/// Checks if an expression is "branchy", e.g. loop, match/if/etc.
+fn is_branchy(expr: &hir::Expr<'_>) -> bool {
+    matches!(
+        expr.kind,
+        hir::ExprKind::If(..) | hir::ExprKind::Loop(..) | hir::ExprKind::Match(..)
+    )
+}
+
 /// Checks if the lines immediately preceding the block contain a safety comment.
-fn block_has_safety_comment(cx: &LateContext<'_>, block: &hir::Block<'_>) -> bool {
+fn block_has_safety_comment(cx: &LateContext<'_>, span: Span) -> bool {
     // This intentionally ignores text before the start of a function so something like:
     // ```
     //     // SAFETY: reason
@@ -136,7 +180,7 @@ fn block_has_safety_comment(cx: &LateContext<'_>, block: &hir::Block<'_>) -> boo
     // won't work. This is to avoid dealing with where such a comment should be place relative to
     // attributes and doc comments.
 
-    span_from_macro_expansion_has_safety_comment(cx, block.span) || span_in_body_has_safety_comment(cx, block.span)
+    span_from_macro_expansion_has_safety_comment(cx, span) || span_in_body_has_safety_comment(cx, span)
 }
 
 /// Checks if the lines immediately preceding the item contain a safety comment.

tests/ui/undocumented_unsafe_blocks.rs

@@ -490,4 +490,20 @@ unsafe impl CrateRoot for () {}
 // SAFETY: ok
 unsafe impl CrateRoot for (i32) {}
 
+fn issue_9142() {
+    // SAFETY: ok
+    let _ = unsafe {};
+
+    // SAFETY: ok
+    let _ = {
+        if unsafe { true } {
+            todo!();
+        } else {
+            let bar = unsafe {};
+            todo!();
+            bar
+        }
+    };
+}
+
 fn main() {}

tests/ui/undocumented_unsafe_blocks.stderr

@@ -263,5 +263,21 @@ LL | unsafe impl CrateRoot for () {}
    |
    = help: consider adding a safety comment on the preceding line
 
-error: aborting due to 31 previous errors
+error: unsafe block missing a safety comment
+  --> $DIR/undocumented_unsafe_blocks.rs:499:12
+   |
+LL |         if unsafe { true } {
+   |            ^^^^^^^^^^^^^^^
+   |
+   = help: consider adding a safety comment on the preceding line
+
+error: unsafe block missing a safety comment
+  --> $DIR/undocumented_unsafe_blocks.rs:502:23
+   |
+LL |             let bar = unsafe {};
+   |                       ^^^^^^^^^
+   |
+   = help: consider adding a safety comment on the preceding line
+
+error: aborting due to 33 previous errors