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undocumented_unsafe_blocks.rs
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undocumented_unsafe_blocks.rs
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use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
use clippy_utils::is_lint_allowed;
use clippy_utils::source::{indent_of, reindent_multiline, snippet};
use rustc_errors::Applicability;
use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc_hir::{Block, BlockCheckMode, Expr, ExprKind, HirId, Local, UnsafeSource};
use rustc_lexer::TokenKind;
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::hir::map::Map;
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::TyCtxt;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::{BytePos, Span};
use std::borrow::Cow;
declare_clippy_lint! {
/// ### What it does
/// Checks for `unsafe` blocks without a `// Safety: ` comment
/// explaining why the unsafe operations performed inside
/// the block are safe.
///
/// ### Why is this bad?
/// Undocumented unsafe blocks can make it difficult to
/// read and maintain code, as well as uncover unsoundness
/// and bugs.
///
/// ### Example
/// ```rust
/// use std::ptr::NonNull;
/// let a = &mut 42;
///
/// let ptr = unsafe { NonNull::new_unchecked(a) };
/// ```
/// Use instead:
/// ```rust
/// use std::ptr::NonNull;
/// let a = &mut 42;
///
/// // Safety: references are guaranteed to be non-null.
/// let ptr = unsafe { NonNull::new_unchecked(a) };
/// ```
#[clippy::version = "1.58.0"]
pub UNDOCUMENTED_UNSAFE_BLOCKS,
restriction,
"creating an unsafe block without explaining why it is safe"
}
impl_lint_pass!(UndocumentedUnsafeBlocks => [UNDOCUMENTED_UNSAFE_BLOCKS]);
#[derive(Default)]
pub struct UndocumentedUnsafeBlocks {
pub local_level: u32,
pub local_span: Option<Span>,
// The local was already checked for an overall safety comment
// There is no need to continue checking the blocks in the local
pub local_checked: bool,
// Since we can only check the blocks from expanded macros
// We have to omit the suggestion due to the actual definition
// Not being available to us
pub macro_expansion: bool,
}
impl LateLintPass<'_> for UndocumentedUnsafeBlocks {
fn check_block(&mut self, cx: &LateContext<'_>, block: &'_ Block<'_>) {
if_chain! {
if !self.local_checked;
if !is_lint_allowed(cx, UNDOCUMENTED_UNSAFE_BLOCKS, block.hir_id);
if !in_external_macro(cx.tcx.sess, block.span);
if let BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided) = block.rules;
if let Some(enclosing_scope_hir_id) = cx.tcx.hir().get_enclosing_scope(block.hir_id);
if self.block_has_safety_comment(cx.tcx, enclosing_scope_hir_id, block.span) == Some(false);
then {
let mut span = block.span;
if let Some(local_span) = self.local_span {
span = local_span;
let result = self.block_has_safety_comment(cx.tcx, enclosing_scope_hir_id, span);
if result.unwrap_or(true) {
self.local_checked = true;
return;
}
}
self.lint(cx, span);
}
}
}
fn check_local(&mut self, cx: &LateContext<'_>, local: &'_ Local<'_>) {
if_chain! {
if !is_lint_allowed(cx, UNDOCUMENTED_UNSAFE_BLOCKS, local.hir_id);
if !in_external_macro(cx.tcx.sess, local.span);
if let Some(init) = local.init;
then {
self.visit_expr(init);
if self.local_level > 0 {
self.local_span = Some(local.span);
}
}
}
}
fn check_block_post(&mut self, _: &LateContext<'_>, _: &'_ Block<'_>) {
self.local_level = self.local_level.saturating_sub(1);
if self.local_level == 0 {
self.local_checked = false;
self.local_span = None;
}
}
}
impl<'hir> Visitor<'hir> for UndocumentedUnsafeBlocks {
type Map = Map<'hir>;
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
fn visit_expr(&mut self, ex: &'v Expr<'v>) {
match ex.kind {
ExprKind::Block(_, _) => self.local_level = self.local_level.saturating_add(1),
_ => walk_expr(self, ex),
}
}
}
impl UndocumentedUnsafeBlocks {
fn block_has_safety_comment(&mut self, tcx: TyCtxt<'_>, enclosing_hir_id: HirId, block_span: Span) -> Option<bool> {
let map = tcx.hir();
let source_map = tcx.sess.source_map();
let enclosing_scope_span = map.opt_span(enclosing_hir_id)?;
let between_span = if block_span.from_expansion() {
self.macro_expansion = true;
enclosing_scope_span.with_hi(block_span.hi())
} else {
self.macro_expansion = false;
enclosing_scope_span.to(block_span)
};
let file_name = source_map.span_to_filename(between_span);
let source_file = source_map.get_source_file(&file_name)?;
let lex_start = (between_span.lo().0 - source_file.start_pos.0 + 1) as usize;
let lex_end = (between_span.hi().0 - source_file.start_pos.0) as usize;
let src_str = source_file.src.as_ref()?[lex_start..lex_end].to_string();
let source_start_pos = source_file.start_pos.0 as usize + lex_start;
let mut pos = 0;
let mut comment = false;
for token in rustc_lexer::tokenize(&src_str) {
match token.kind {
TokenKind::LineComment { doc_style: None }
| TokenKind::BlockComment {
doc_style: None,
terminated: true,
} => {
let comment_str = src_str[pos + 2..pos + token.len].to_ascii_uppercase();
if comment_str.contains("SAFETY:") {
comment = true;
}
},
// We need to add all whitespace to `pos` before checking the comment's line number
TokenKind::Whitespace => {},
_ => {
if comment {
// Get the line number of the "comment" (really wherever the trailing whitespace ended)
let comment_line_num = source_file
.lookup_file_pos(BytePos((source_start_pos + pos).try_into().unwrap()))
.0;
// Find the block/local's line number
let block_line_num = tcx.sess.source_map().lookup_char_pos(block_span.lo()).line;
// Check the comment is immediately followed by the block/local
if block_line_num == comment_line_num + 1 || block_line_num == comment_line_num {
return Some(true);
}
comment = false;
}
},
}
pos += token.len;
}
Some(false)
}
fn lint(&self, cx: &LateContext<'_>, mut span: Span) {
let source_map = cx.tcx.sess.source_map();
if source_map.is_multiline(span) {
span = source_map.span_until_char(span, '\n');
}
if self.macro_expansion {
span_lint_and_help(
cx,
UNDOCUMENTED_UNSAFE_BLOCKS,
span,
"unsafe block in macro expansion missing a safety comment",
None,
"consider adding a safety comment in the macro definition",
);
} else {
let block_indent = indent_of(cx, span);
let suggestion = format!("// Safety: ...\n{}", snippet(cx, span, ".."));
span_lint_and_sugg(
cx,
UNDOCUMENTED_UNSAFE_BLOCKS,
span,
"unsafe block missing a safety comment",
"consider adding a safety comment",
reindent_multiline(Cow::Borrowed(&suggestion), true, block_indent).to_string(),
Applicability::HasPlaceholders,
);
}
}
}