Basic support for type: ignore comments (#15046)

## Summary

This PR adds initial support for `type: ignore`. It doesn't do anything
fancy yet like:

* Detecting invalid type ignore comments
* Detecting type ignore comments that are part of another suppression
comment: `# fmt: skip # type: ignore`
* Suppressing specific lints `type: ignore [code]`
* Detecting unsused type ignore comments
* ...

The goal is to add this functionality in separate PRs.

## Test Plan

---------

Co-authored-by: Carl Meyer <carl@astral.sh>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/red_knot_python_semantic/src/suppression.rs

@@ -1,50 +1,104 @@
-use salsa;
+use ruff_python_parser::TokenKind;
+use ruff_source_file::LineRanges;
+use ruff_text_size::{Ranged, TextRange};
 
-use ruff_db::{files::File, parsed::comment_ranges, source::source_text};
-use ruff_index::{newtype_index, IndexVec};
+use ruff_db::{files::File, parsed::parsed_module, source::source_text};
 
 use crate::{lint::LintId, Db};
 
 #[salsa::tracked(return_ref)]
-pub(crate) fn suppressions(db: &dyn Db, file: File) -> IndexVec<SuppressionIndex, Suppression> {
-    let comments = comment_ranges(db.upcast(), file);
+pub(crate) fn suppressions(db: &dyn Db, file: File) -> Suppressions {
     let source = source_text(db.upcast(), file);
+    let parsed = parsed_module(db.upcast(), file);
 
-    let mut suppressions = IndexVec::default();
+    // TODO: Support `type: ignore` comments at the
+    //   [start of the file](https://typing.readthedocs.io/en/latest/spec/directives.html#type-ignore-comments).
+    let mut suppressions = Vec::default();
+    let mut line_start = source.bom_start_offset();
 
-    for range in comments {
-        let text = &source[range];
+    for token in parsed.tokens() {
+        match token.kind() {
+            TokenKind::Comment => {
+                let text = &source[token.range()];
 
-        if text.starts_with("# type: ignore") {
-            suppressions.push(Suppression {
-                target: None,
-                kind: SuppressionKind::TypeIgnore,
-            });
-        } else if text.starts_with("# knot: ignore") {
-            suppressions.push(Suppression {
-                target: None,
-                kind: SuppressionKind::KnotIgnore,
-            });
+                let suppressed_range = TextRange::new(line_start, token.end());
+
+                if text.strip_prefix("# type: ignore").is_some_and(|suffix| {
+                    suffix.is_empty()
+                        || suffix.starts_with(char::is_whitespace)
+                        || suffix.starts_with('[')
+                }) {
+                    suppressions.push(Suppression { suppressed_range });
+                }
+            }
+            TokenKind::Newline | TokenKind::NonLogicalNewline => {
+                line_start = token.end();
+            }
+            _ => {}
         }
     }
 
-    suppressions
+    Suppressions { suppressions }
 }
 
-#[newtype_index]
-pub(crate) struct SuppressionIndex;
+/// The suppression comments of a single file.
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub(crate) struct Suppressions {
+    /// The suppressions sorted by the suppressed range.
+    suppressions: Vec<Suppression>,
+}
 
+impl Suppressions {
+    /// Finds a suppression for the specified lint.
+    ///
+    /// Returns the first matching suppression if more than one suppression apply to `range` and `id`.
+    ///
+    /// Returns `None` if the lint isn't suppressed.
+    pub(crate) fn find_suppression(&self, range: TextRange, _id: LintId) -> Option<&Suppression> {
+        // TODO(micha):
+        //   * Test if the suppression suppresses the passed lint
+        self.for_range(range).next()
+    }
+
+    /// Returns all suppression comments that apply for `range`.
+    ///
+    /// A suppression applies for the given range if it contains the range's
+    /// start or end offset. This means the suppression is on the same line
+    /// as the diagnostic's start or end.
+    fn for_range(&self, range: TextRange) -> impl Iterator<Item = &Suppression> + '_ {
+        // First find the index of the suppression comment that ends right before the range
+        // starts. This allows us to skip suppressions that are not relevant for the range.
+        let end_offset = self
+            .suppressions
+            .binary_search_by_key(&range.start(), |suppression| {
+                suppression.suppressed_range.end()
+            })
+            .unwrap_or_else(|index| index);
+
+        // From here, search the remaining suppression comments for one that
+        // contains the range's start or end offset. Stop the search
+        // as soon as the suppression's range and the range no longer overlap.
+        self.suppressions[end_offset..]
+            .iter()
+            // Stop searching if the suppression starts after the range we're looking for.
+            .take_while(move |suppression| range.end() >= suppression.suppressed_range.start())
+            .filter(move |suppression| {
+                // Don't use intersect to avoid that suppressions on inner-expression
+                // ignore errors for outer expressions
+                suppression.suppressed_range.contains(range.start())
+                    || suppression.suppressed_range.contains(range.end())
+            })
+    }
+}
+
+/// A `type: ignore` or `knot: ignore` suppression comment.
 #[derive(Clone, Debug, Eq, PartialEq, Hash)]
 pub(crate) struct Suppression {
-    target: Option<LintId>,
-    kind: SuppressionKind,
-}
-
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
-pub(crate) enum SuppressionKind {
-    /// A `type: ignore` comment
-    TypeIgnore,
-
-    /// A `knot: ignore` comment
-    KnotIgnore,
+    /// The range for which this suppression applies.
+    /// Most of the time, this is the range of the comment's line.
+    /// However, there are few cases where the range gets expanded to
+    /// cover multiple lines:
+    /// * multiline strings: `expr + """multiline\nstring"""  # type: ignore`
+    /// * line continuations: `expr \ + "test"  # type: ignore`
+    suppressed_range: TextRange,
 }