src/tools/clippy/clippy_lints/src/undocumented_unsafe_blocks.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::source::walk_span_to_context;
   3 use clippy_utils::{get_parent_node, is_lint_allowed};
   4 use rustc_data_structures::sync::Lrc;
   5 use rustc_hir as hir;
   6 use rustc_hir::{Block, BlockCheckMode, ItemKind, Node, UnsafeSource};
   7 use rustc_lexer::{tokenize, TokenKind};
   8 use rustc_lint::{LateContext, LateLintPass, LintContext};
   9 use rustc_middle::lint::in_external_macro;
  10 use rustc_session::{declare_lint_pass, declare_tool_lint};
  11 use rustc_span::{BytePos, Pos, Span, SyntaxContext};
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  15     /// Checks for `unsafe` blocks and impls without a `// SAFETY: ` comment
  16     /// explaining why the unsafe operations performed inside
  17     /// the block are safe.
  18     ///
  19     /// Note the comment must appear on the line(s) preceding the unsafe block
  20     /// with nothing appearing in between. The following is ok:
  21     /// ```ignore
  22     /// foo(
  23     ///     // SAFETY:
  24     ///     // This is a valid safety comment
  25     ///     unsafe { *x }
  26     /// )
  27     /// ```
  28     /// But neither of these are:
  29     /// ```ignore
  30     /// // SAFETY:
  31     /// // This is not a valid safety comment
  32     /// foo(
  33     ///     /* SAFETY: Neither is this */ unsafe { *x },
  34     /// );
  35     /// ```
  36     ///
  37     /// ### Why is this bad?
  38     /// Undocumented unsafe blocks and impls can make it difficult to
  39     /// read and maintain code, as well as uncover unsoundness
  40     /// and bugs.
  41     ///
  42     /// ### Example
  43     /// ```rust
  44     /// use std::ptr::NonNull;
  45     /// let a = &mut 42;
  46     ///
  47     /// let ptr = unsafe { NonNull::new_unchecked(a) };
  48     /// ```
  49     /// Use instead:
  50     /// ```rust
  51     /// use std::ptr::NonNull;
  52     /// let a = &mut 42;
  53     ///
  54     /// // SAFETY: references are guaranteed to be non-null.
  55     /// let ptr = unsafe { NonNull::new_unchecked(a) };
  56     /// ```
  57     #[clippy::version = "1.58.0"]
  58     pub UNDOCUMENTED_UNSAFE_BLOCKS,
  59     restriction,
  60     "creating an unsafe block without explaining why it is safe"
  61 }
  62
  63 declare_lint_pass!(UndocumentedUnsafeBlocks => [UNDOCUMENTED_UNSAFE_BLOCKS]);
  64
  65 impl LateLintPass<'_> for UndocumentedUnsafeBlocks {
  66     fn check_block(&mut self, cx: &LateContext<'_>, block: &'_ Block<'_>) {
  67         if block.rules == BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided)
  68             && !in_external_macro(cx.tcx.sess, block.span)
  69             && !is_lint_allowed(cx, UNDOCUMENTED_UNSAFE_BLOCKS, block.hir_id)
  70             && !is_unsafe_from_proc_macro(cx, block.span)
  71             && !block_has_safety_comment(cx, block)
  72         {
  73             let source_map = cx.tcx.sess.source_map();
  74             let span = if source_map.is_multiline(block.span) {
  75                 source_map.span_until_char(block.span, '\n')
  76             } else {
  77                 block.span
  78             };
  79
  80             span_lint_and_help(
  81                 cx,
  82                 UNDOCUMENTED_UNSAFE_BLOCKS,
  83                 span,
  84                 "unsafe block missing a safety comment",
  85                 None,
  86                 "consider adding a safety comment on the preceding line",
  87             );
  88         }
  89     }
  90
  91     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
  92         if let hir::ItemKind::Impl(imple) = item.kind
  93             && imple.unsafety == hir::Unsafety::Unsafe
  94             && !in_external_macro(cx.tcx.sess, item.span)
  95             && !is_lint_allowed(cx, UNDOCUMENTED_UNSAFE_BLOCKS, item.hir_id())
  96             && !is_unsafe_from_proc_macro(cx, item.span)
  97             && !item_has_safety_comment(cx, item)
  98         {
  99             let source_map = cx.tcx.sess.source_map();
 100             let span = if source_map.is_multiline(item.span) {
 101                 source_map.span_until_char(item.span, '\n')
 102             } else {
 103                 item.span
 104             };
 105
 106             span_lint_and_help(
 107                 cx,
 108                 UNDOCUMENTED_UNSAFE_BLOCKS,
 109                 span,
 110                 "unsafe impl missing a safety comment",
 111                 None,
 112                 "consider adding a safety comment on the preceding line",
 113             );
 114         }
 115     }
 116 }
 117
 118 fn is_unsafe_from_proc_macro(cx: &LateContext<'_>, span: Span) -> bool {
 119     let source_map = cx.sess().source_map();
 120     let file_pos = source_map.lookup_byte_offset(span.lo());
 121     file_pos
 122         .sf
 123         .src
 124         .as_deref()
 125         .and_then(|src| src.get(file_pos.pos.to_usize()..))
 126         .map_or(true, |src| !src.starts_with("unsafe"))
 127 }
 128
 129 /// Checks if the lines immediately preceding the block contain a safety comment.
 130 fn block_has_safety_comment(cx: &LateContext<'_>, block: &hir::Block<'_>) -> bool {
 131     // This intentionally ignores text before the start of a function so something like:
 132     // ```
 133     //     // SAFETY: reason
 134     //     fn foo() { unsafe { .. } }
 135     // ```
 136     // won't work. This is to avoid dealing with where such a comment should be place relative to
 137     // attributes and doc comments.
 138
 139     span_from_macro_expansion_has_safety_comment(cx, block.span) || span_in_body_has_safety_comment(cx, block.span)
 140 }
 141
 142 /// Checks if the lines immediately preceding the item contain a safety comment.
 143 #[allow(clippy::collapsible_match)]
 144 fn item_has_safety_comment(cx: &LateContext<'_>, item: &hir::Item<'_>) -> bool {
 145     if span_from_macro_expansion_has_safety_comment(cx, item.span) {
 146         return true;
 147     }
 148
 149     if item.span.ctxt() == SyntaxContext::root() {
 150         if let Some(parent_node) = get_parent_node(cx.tcx, item.hir_id()) {
 151             let comment_start = match parent_node {
 152                 Node::Crate(parent_mod) => {
 153                     comment_start_before_impl_in_mod(cx, parent_mod, parent_mod.spans.inner_span, item)
 154                 },
 155                 Node::Item(parent_item) => {
 156                     if let ItemKind::Mod(parent_mod) = &parent_item.kind {
 157                         comment_start_before_impl_in_mod(cx, parent_mod, parent_item.span, item)
 158                     } else {
 159                         // Doesn't support impls in this position. Pretend a comment was found.
 160                         return true;
 161                     }
 162                 },
 163                 Node::Stmt(stmt) => {
 164                     if let Some(stmt_parent) = get_parent_node(cx.tcx, stmt.hir_id) {
 165                         match stmt_parent {
 166                             Node::Block(block) => walk_span_to_context(block.span, SyntaxContext::root()).map(Span::lo),
 167                             _ => {
 168                                 // Doesn't support impls in this position. Pretend a comment was found.
 169                                 return true;
 170                             },
 171                         }
 172                     } else {
 173                         // Problem getting the parent node. Pretend a comment was found.
 174                         return true;
 175                     }
 176                 },
 177                 _ => {
 178                     // Doesn't support impls in this position. Pretend a comment was found.
 179                     return true;
 180                 },
 181             };
 182
 183             let source_map = cx.sess().source_map();
 184             if let Some(comment_start) = comment_start
 185                 && let Ok(unsafe_line) = source_map.lookup_line(item.span.lo())
 186                 && let Ok(comment_start_line) = source_map.lookup_line(comment_start)
 187                 && Lrc::ptr_eq(&unsafe_line.sf, &comment_start_line.sf)
 188                 && let Some(src) = unsafe_line.sf.src.as_deref()
 189             {
 190                 comment_start_line.line < unsafe_line.line && text_has_safety_comment(
 191                     src,
 192                     &unsafe_line.sf.lines[comment_start_line.line + 1..=unsafe_line.line],
 193                     unsafe_line.sf.start_pos.to_usize(),
 194                 )
 195             } else {
 196                 // Problem getting source text. Pretend a comment was found.
 197                 true
 198             }
 199         } else {
 200             // No parent node. Pretend a comment was found.
 201             true
 202         }
 203     } else {
 204         false
 205     }
 206 }
 207
 208 fn comment_start_before_impl_in_mod(
 209     cx: &LateContext<'_>,
 210     parent_mod: &hir::Mod<'_>,
 211     parent_mod_span: Span,
 212     imple: &hir::Item<'_>,
 213 ) -> Option<BytePos> {
 214     parent_mod.item_ids.iter().enumerate().find_map(|(idx, item_id)| {
 215         if *item_id == imple.item_id() {
 216             if idx == 0 {
 217                 // mod A { /* comment */ unsafe impl T {} ... }
 218                 // ^------------------------------------------^ returns the start of this span
 219                 // ^---------------------^ finally checks comments in this range
 220                 if let Some(sp) = walk_span_to_context(parent_mod_span, SyntaxContext::root()) {
 221                     return Some(sp.lo());
 222                 }
 223             } else {
 224                 // some_item /* comment */ unsafe impl T {}
 225                 // ^-------^ returns the end of this span
 226                 //         ^---------------^ finally checks comments in this range
 227                 let prev_item = cx.tcx.hir().item(parent_mod.item_ids[idx - 1]);
 228                 if let Some(sp) = walk_span_to_context(prev_item.span, SyntaxContext::root()) {
 229                     return Some(sp.hi());
 230                 }
 231             }
 232         }
 233         None
 234     })
 235 }
 236
 237 fn span_from_macro_expansion_has_safety_comment(cx: &LateContext<'_>, span: Span) -> bool {
 238     let source_map = cx.sess().source_map();
 239     let ctxt = span.ctxt();
 240     if ctxt == SyntaxContext::root() {
 241         false
 242     } else {
 243         // From a macro expansion. Get the text from the start of the macro declaration to start of the
 244         // unsafe block.
 245         //     macro_rules! foo { () => { stuff }; (x) => { unsafe { stuff } }; }
 246         //     ^--------------------------------------------^
 247         if let Ok(unsafe_line) = source_map.lookup_line(span.lo())
 248             && let Ok(macro_line) = source_map.lookup_line(ctxt.outer_expn_data().def_site.lo())
 249             && Lrc::ptr_eq(&unsafe_line.sf, &macro_line.sf)
 250             && let Some(src) = unsafe_line.sf.src.as_deref()
 251         {
 252             macro_line.line < unsafe_line.line && text_has_safety_comment(
 253                 src,
 254                 &unsafe_line.sf.lines[macro_line.line + 1..=unsafe_line.line],
 255                 unsafe_line.sf.start_pos.to_usize(),
 256             )
 257         } else {
 258             // Problem getting source text. Pretend a comment was found.
 259             true
 260         }
 261     }
 262 }
 263
 264 fn span_in_body_has_safety_comment(cx: &LateContext<'_>, span: Span) -> bool {
 265     let source_map = cx.sess().source_map();
 266     let ctxt = span.ctxt();
 267     if ctxt == SyntaxContext::root()
 268         && let Some(body) = cx.enclosing_body
 269     {
 270         if let Ok(unsafe_line) = source_map.lookup_line(span.lo())
 271             && let Some(body_span) = walk_span_to_context(cx.tcx.hir().body(body).value.span, SyntaxContext::root())
 272             && let Ok(body_line) = source_map.lookup_line(body_span.lo())
 273             && Lrc::ptr_eq(&unsafe_line.sf, &body_line.sf)
 274             && let Some(src) = unsafe_line.sf.src.as_deref()
 275         {
 276             // Get the text from the start of function body to the unsafe block.
 277             //     fn foo() { some_stuff; unsafe { stuff }; other_stuff; }
 278             //              ^-------------^
 279             body_line.line < unsafe_line.line && text_has_safety_comment(
 280                 src,
 281                 &unsafe_line.sf.lines[body_line.line + 1..=unsafe_line.line],
 282                 unsafe_line.sf.start_pos.to_usize(),
 283             )
 284         } else {
 285             // Problem getting source text. Pretend a comment was found.
 286             true
 287         }
 288     } else {
 289         false
 290     }
 291 }
 292
 293 /// Checks if the given text has a safety comment for the immediately proceeding line.
 294 fn text_has_safety_comment(src: &str, line_starts: &[BytePos], offset: usize) -> bool {
 295     let mut lines = line_starts
 296         .array_windows::<2>()
 297         .rev()
 298         .map_while(|[start, end]| {
 299             let start = start.to_usize() - offset;
 300             let end = end.to_usize() - offset;
 301             src.get(start..end).map(|text| (start, text.trim_start()))
 302         })
 303         .filter(|(_, text)| !text.is_empty());
 304
 305     let Some((line_start, line)) = lines.next() else {
 306         return false;
 307     };
 308     // Check for a sequence of line comments.
 309     if line.starts_with("//") {
 310         let mut line = line;
 311         loop {
 312             if line.to_ascii_uppercase().contains("SAFETY:") {
 313                 return true;
 314             }
 315             match lines.next() {
 316                 Some((_, x)) if x.starts_with("//") => line = x,
 317                 _ => return false,
 318             }
 319         }
 320     }
 321     // No line comments; look for the start of a block comment.
 322     // This will only find them if they are at the start of a line.
 323     let (mut line_start, mut line) = (line_start, line);
 324     loop {
 325         if line.starts_with("/*") {
 326             let src = src[line_start..line_starts.last().unwrap().to_usize() - offset].trim_start();
 327             let mut tokens = tokenize(src);
 328             return src[..tokens.next().unwrap().len]
 329                 .to_ascii_uppercase()
 330                 .contains("SAFETY:")
 331                 && tokens.all(|t| t.kind == TokenKind::Whitespace);
 332         }
 333         match lines.next() {
 334             Some(x) => (line_start, line) = x,
 335             None => return false,
 336         }
 337     }
 338 }