Auto merge of #12770 - notriddle:notriddle/doc-lazy-continuation, r=llogiq

Add new lint `doc_lazy_continuation`

changelog: [`doc_lazy_continuation`]: add lint that warns on so-called "lazy paragraph continuations"

This is a follow-up for #121659, since most cases of unintended block quotes are lazy continuations. The lint is designed to be more generally useful than that, though, because it will also catch unintended list items and unintended block quotes that didn't coincidentally hit a pulldown-cmark bug.

The second commit is the result of running `cargo dev dogfood --fix`, and manually fixing anything that seems wrong. NOTE: this lint's suggestions should never change the parser's interpretation of the markdown, but in many cases, it seems that doc comments in clippy were written without regard for this feature of Markdown (which, I suppose, is why this lint should exist).

Author: bors

CHANGELOG.md

@@ -5249,6 +5249,7 @@ Released 2018-09-13
 [`disallowed_type`]: https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_type
 [`disallowed_types`]: https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_types
 [`diverging_sub_expression`]: https://rust-lang.github.io/rust-clippy/master/index.html#diverging_sub_expression
+[`doc_lazy_continuation`]: https://rust-lang.github.io/rust-clippy/master/index.html#doc_lazy_continuation
 [`doc_link_with_quotes`]: https://rust-lang.github.io/rust-clippy/master/index.html#doc_link_with_quotes
 [`doc_markdown`]: https://rust-lang.github.io/rust-clippy/master/index.html#doc_markdown
 [`double_comparisons`]: https://rust-lang.github.io/rust-clippy/master/index.html#double_comparisons

clippy_lints/src/casts/cast_sign_loss.rs

@@ -255,8 +255,10 @@ fn expr_add_sign(cx: &LateContext<'_>, expr: &Expr<'_>) -> Sign {
 
 /// Peels binary operators such as [`BinOpKind::Mul`], [`BinOpKind::Div`] or [`BinOpKind::Rem`],
 /// where the result depends on:
+///
 /// - the number of negative values in the entire expression, or
 /// - the number of negative values on the left hand side of the expression.
+///
 /// Ignores overflow.
 ///
 ///
@@ -303,8 +305,10 @@ fn exprs_with_muldiv_binop_peeled<'e>(expr: &'e Expr<'_>) -> Vec<&'e Expr<'e>> {
 }
 
 /// Peels binary operators such as [`BinOpKind::Add`], where the result depends on:
+///
 /// - all the expressions being positive, or
 /// - all the expressions being negative.
+///
 /// Ignores overflow.
 ///
 /// Expressions using other operators are preserved, so we can try to evaluate them later.

clippy_lints/src/declared_lints.rs

@@ -140,6 +140,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::disallowed_names::DISALLOWED_NAMES_INFO,
     crate::disallowed_script_idents::DISALLOWED_SCRIPT_IDENTS_INFO,
     crate::disallowed_types::DISALLOWED_TYPES_INFO,
+    crate::doc::DOC_LAZY_CONTINUATION_INFO,
     crate::doc::DOC_LINK_WITH_QUOTES_INFO,
     crate::doc::DOC_MARKDOWN_INFO,
     crate::doc::EMPTY_DOCS_INFO,

clippy_lints/src/doc/lazy_continuation.rs

@@ -0,0 +1,95 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use itertools::Itertools;
+use rustc_errors::{Applicability, SuggestionStyle};
+use rustc_lint::LateContext;
+use rustc_span::{BytePos, Span};
+use std::ops::Range;
+
+use super::DOC_LAZY_CONTINUATION;
+
+fn map_container_to_text(c: &super::Container) -> &'static str {
+    match c {
+        super::Container::Blockquote => "> ",
+        // numbered list can have up to nine digits, plus the dot, plus four spaces on either side
+        super::Container::List(indent) => &"                  "[0..*indent],
+    }
+}
+
+// TODO: Adjust the parameters as necessary
+pub(super) fn check(
+    cx: &LateContext<'_>,
+    doc: &str,
+    range: Range<usize>,
+    mut span: Span,
+    containers: &[super::Container],
+) {
+    if doc[range.clone()].contains('\t') {
+        // We don't do tab stops correctly.
+        return;
+    }
+
+    let ccount = doc[range.clone()].chars().filter(|c| *c == '>').count();
+    let blockquote_level = containers
+        .iter()
+        .filter(|c| matches!(c, super::Container::Blockquote))
+        .count();
+    let lcount = doc[range.clone()].chars().filter(|c| *c == ' ').count();
+    let list_indentation = containers
+        .iter()
+        .map(|c| {
+            if let super::Container::List(indent) = c {
+                *indent
+            } else {
+                0
+            }
+        })
+        .sum();
+    if ccount < blockquote_level || lcount < list_indentation {
+        let msg = if ccount < blockquote_level {
+            "doc quote missing `>` marker"
+        } else {
+            "doc list item missing indentation"
+        };
+        span_lint_and_then(cx, DOC_LAZY_CONTINUATION, span, msg, |diag| {
+            if ccount == 0 && blockquote_level == 0 {
+                // simpler suggestion style for indentation
+                let indent = list_indentation - lcount;
+                diag.span_suggestion_with_style(
+                    span.shrink_to_hi(),
+                    "indent this line",
+                    std::iter::repeat(" ").take(indent).join(""),
+                    Applicability::MaybeIncorrect,
+                    SuggestionStyle::ShowAlways,
+                );
+                diag.help("if this is supposed to be its own paragraph, add a blank line");
+                return;
+            }
+            let mut doc_start_range = &doc[range];
+            let mut suggested = String::new();
+            for c in containers {
+                let text = map_container_to_text(c);
+                if doc_start_range.starts_with(text) {
+                    doc_start_range = &doc_start_range[text.len()..];
+                    span = span
+                        .with_lo(span.lo() + BytePos(u32::try_from(text.len()).expect("text is not 2**32 or bigger")));
+                } else if matches!(c, super::Container::Blockquote)
+                    && let Some(i) = doc_start_range.find('>')
+                {
+                    doc_start_range = &doc_start_range[i + 1..];
+                    span =
+                        span.with_lo(span.lo() + BytePos(u32::try_from(i).expect("text is not 2**32 or bigger") + 1));
+                } else {
+                    suggested.push_str(text);
+                }
+            }
+            diag.span_suggestion_with_style(
+                span,
+                "add markers to start of line",
+                suggested,
+                Applicability::MachineApplicable,
+                SuggestionStyle::ShowAlways,
+            );
+            diag.help("if this not intended to be a quote at all, escape it with `\\>`");
+        });
+    }
+}

clippy_lints/src/doc/mod.rs

@@ -1,3 +1,4 @@
+mod lazy_continuation;
 use clippy_utils::attrs::is_doc_hidden;
 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
 use clippy_utils::macros::{is_panic, root_macro_call_first_node};
@@ -7,7 +8,7 @@ use clippy_utils::{is_entrypoint_fn, is_trait_impl_item, method_chain_args};
 use pulldown_cmark::Event::{
     Code, End, FootnoteReference, HardBreak, Html, Rule, SoftBreak, Start, TaskListMarker, Text,
 };
-use pulldown_cmark::Tag::{BlockQuote, CodeBlock, Heading, Item, Link, Paragraph};
+use pulldown_cmark::Tag::{BlockQuote, CodeBlock, FootnoteDefinition, Heading, Item, Link, Paragraph};
 use pulldown_cmark::{BrokenLink, CodeBlockKind, CowStr, Options};
 use rustc_ast::ast::Attribute;
 use rustc_data_structures::fx::FxHashSet;
@@ -362,6 +363,63 @@ declare_clippy_lint! {
     "docstrings exist but documentation is empty"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    ///
+    /// In CommonMark Markdown, the language used to write doc comments, a
+    /// paragraph nested within a list or block quote does not need any line
+    /// after the first one to be indented or marked. The specification calls
+    /// this a "lazy paragraph continuation."
+    ///
+    /// ### Why is this bad?
+    ///
+    /// This is easy to write but hard to read. Lazy continuations makes
+    /// unintended markers hard to see, and make it harder to deduce the
+    /// document's intended structure.
+    ///
+    /// ### Example
+    ///
+    /// This table is probably intended to have two rows,
+    /// but it does not. It has zero rows, and is followed by
+    /// a block quote.
+    /// ```no_run
+    /// /// Range | Description
+    /// /// ----- | -----------
+    /// /// >= 1  | fully opaque
+    /// /// < 1   | partially see-through
+    /// fn set_opacity(opacity: f32) {}
+    /// ```
+    ///
+    /// Fix it by escaping the marker:
+    /// ```no_run
+    /// /// Range | Description
+    /// /// ----- | -----------
+    /// /// \>= 1 | fully opaque
+    /// /// < 1   | partially see-through
+    /// fn set_opacity(opacity: f32) {}
+    /// ```
+    ///
+    /// This example is actually intended to be a list:
+    /// ```no_run
+    /// /// * Do nothing.
+    /// /// * Then do something. Whatever it is needs done,
+    /// /// it should be done right now.
+    /// # fn do_stuff() {}
+    /// ```
+    ///
+    /// Fix it by indenting the list contents:
+    /// ```no_run
+    /// /// * Do nothing.
+    /// /// * Then do something. Whatever it is needs done,
+    /// ///   it should be done right now.
+    /// # fn do_stuff() {}
+    /// ```
+    #[clippy::version = "1.80.0"]
+    pub DOC_LAZY_CONTINUATION,
+    style,
+    "require every line of a paragraph to be indented and marked"
+}
+
 #[derive(Clone)]
 pub struct Documentation {
     valid_idents: FxHashSet<String>,
@@ -388,6 +446,7 @@ impl_lint_pass!(Documentation => [
     UNNECESSARY_SAFETY_DOC,
     SUSPICIOUS_DOC_COMMENTS,
     EMPTY_DOCS,
+    DOC_LAZY_CONTINUATION,
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for Documentation {
@@ -551,6 +610,7 @@ fn check_attrs(cx: &LateContext<'_>, valid_idents: &FxHashSet<String>, attrs: &[
         cx,
         valid_idents,
         parser.into_offset_iter(),
+        &doc,
         Fragments {
             fragments: &fragments,
             doc: &doc,
@@ -560,6 +620,11 @@ fn check_attrs(cx: &LateContext<'_>, valid_idents: &FxHashSet<String>, attrs: &[
 
 const RUST_CODE: &[&str] = &["rust", "no_run", "should_panic", "compile_fail"];
 
+enum Container {
+    Blockquote,
+    List(usize),
+}
+
 /// Checks parsed documentation.
 /// This walks the "events" (think sections of markdown) produced by `pulldown_cmark`,
 /// so lints here will generally access that information.
@@ -569,13 +634,15 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
     cx: &LateContext<'_>,
     valid_idents: &FxHashSet<String>,
     events: Events,
+    doc: &str,
     fragments: Fragments<'_>,
 ) -> DocHeaders {
     // true if a safety header was found
     let mut headers = DocHeaders::default();
     let mut in_code = false;
     let mut in_link = None;
     let mut in_heading = false;
+    let mut in_footnote_definition = false;
     let mut is_rust = false;
     let mut no_test = false;
     let mut ignore = false;
@@ -586,7 +653,11 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
     let mut code_level = 0;
     let mut blockquote_level = 0;
 
-    for (event, range) in events {
+    let mut containers = Vec::new();
+
+    let mut events = events.peekable();
+
+    while let Some((event, range)) = events.next() {
         match event {
             Html(tag) => {
                 if tag.starts_with("<code") {
@@ -599,8 +670,14 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
                     blockquote_level -= 1;
                 }
             },
-            Start(BlockQuote) => blockquote_level += 1,
-            End(BlockQuote) => blockquote_level -= 1,
+            Start(BlockQuote) => {
+                blockquote_level += 1;
+                containers.push(Container::Blockquote);
+            },
+            End(BlockQuote) => {
+                blockquote_level -= 1;
+                containers.pop();
+            },
             Start(CodeBlock(ref kind)) => {
                 in_code = true;
                 if let CodeBlockKind::Fenced(lang) = kind {
@@ -633,13 +710,23 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
                 if let Start(Heading(_, _, _)) = event {
                     in_heading = true;
                 }
+                if let Start(Item) = event {
+                    if let Some((_next_event, next_range)) = events.peek() {
+                        containers.push(Container::List(next_range.start - range.start));
+                    } else {
+                        containers.push(Container::List(0));
+                    }
+                }
                 ticks_unbalanced = false;
                 paragraph_range = range;
             },
             End(Heading(_, _, _) | Paragraph | Item) => {
                 if let End(Heading(_, _, _)) = event {
                     in_heading = false;
                 }
+                if let End(Item) = event {
+                    containers.pop();
+                }
                 if ticks_unbalanced && let Some(span) = fragments.span(cx, paragraph_range.clone()) {
                     span_lint_and_help(
                         cx,
@@ -658,8 +745,26 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
                 }
                 text_to_check = Vec::new();
             },
+            Start(FootnoteDefinition(..)) => in_footnote_definition = true,
+            End(FootnoteDefinition(..)) => in_footnote_definition = false,
             Start(_tag) | End(_tag) => (), // We don't care about other tags
-            SoftBreak | HardBreak | TaskListMarker(_) | Code(_) | Rule => (),
+            SoftBreak | HardBreak => {
+                if !containers.is_empty()
+                    && let Some((_next_event, next_range)) = events.peek()
+                    && let Some(next_span) = fragments.span(cx, next_range.clone())
+                    && let Some(span) = fragments.span(cx, range.clone())
+                    && !in_footnote_definition
+                {
+                    lazy_continuation::check(
+                        cx,
+                        doc,
+                        range.end..next_range.start,
+                        Span::new(span.hi(), next_span.lo(), span.ctxt(), span.parent()),
+                        &containers[..],
+                    );
+                }
+            },
+            TaskListMarker(_) | Code(_) | Rule => (),
             FootnoteReference(text) | Text(text) => {
                 paragraph_range.end = range.end;
                 ticks_unbalanced |= text.contains('`') && !in_code;

clippy_lints/src/manual_clamp.rs

@@ -611,15 +611,22 @@ impl<'tcx> BinaryOp<'tcx> {
 
 /// The clamp meta pattern is a pattern shared between many (but not all) patterns.
 /// In summary, this pattern consists of two if statements that meet many criteria,
+///
 /// - binary operators that are one of [`>`, `<`, `>=`, `<=`].
+///
 /// - Both binary statements must have a shared argument
+///
 ///     - Which can appear on the left or right side of either statement
+///
 ///     - The binary operators must define a finite range for the shared argument. To put this in
 ///       the terms of Rust `std` library, the following ranges are acceptable
+///
 ///         - `Range`
 ///         - `RangeInclusive`
+///
 ///       And all other range types are not accepted. For the purposes of `clamp` it's irrelevant
 ///       whether the range is inclusive or not, the output is the same.
+///
 /// - The result of each if statement must be equal to the argument unique to that if statement. The
 ///   result can not be the shared argument in either case.
 fn is_clamp_meta_pattern<'tcx>(

clippy_lints/src/methods/iter_filter.rs

@@ -126,15 +126,15 @@ enum FilterType {
 ///
 /// How this is done:
 /// 1. we know that this is invoked in a method call with `filter` as the method name via `mod.rs`
-/// 2. we check that we are in a trait method. Therefore we are in an
-/// `(x as Iterator).filter({filter_arg})` method call.
+/// 2. we check that we are in a trait method. Therefore we are in an `(x as
+///    Iterator).filter({filter_arg})` method call.
 /// 3. we check that the parent expression is not a map. This is because we don't want to lint
 ///    twice, and we already have a specialized lint for that.
 /// 4. we check that the span of the filter does not contain a comment.
 /// 5. we get the type of the `Item` in the `Iterator`, and compare against the type of Option and
-///   Result.
+///    Result.
 /// 6. we finally check the contents of the filter argument to see if it is a call to `is_some` or
-///   `is_ok`.
+///    `is_ok`.
 /// 7. if all of the above are true, then we return the `FilterType`
 fn expression_type(
     cx: &LateContext<'_>,

clippy_lints/src/methods/iter_kv_map.rs

@@ -12,8 +12,10 @@ use rustc_middle::ty;
 use rustc_span::{sym, Span};
 
 /// lint use of:
+///
 /// - `hashmap.iter().map(|(_, v)| v)`
 /// - `hashmap.into_iter().map(|(_, v)| v)`
+///
 /// on `HashMaps` and `BTreeMaps` in std
 
 pub(super) fn check<'tcx>(

clippy_lints/src/methods/utils.rs

@@ -120,6 +120,7 @@ fn pat_bindings(pat: &Pat<'_>) -> Vec<HirId> {
 /// operations performed on `binding_hir_ids` are:
 /// * to take non-mutable references to them
 /// * to use them as non-mutable `&self` in method calls
+///
 /// If any of `binding_hir_ids` is used in any other way, then `clone_or_copy_needed` will be true
 /// when `CloneOrCopyVisitor` is done visiting.
 struct CloneOrCopyVisitor<'cx, 'tcx> {