refactor(write): split each lint into its own module

clippy_lints/src/write/empty_string.rs

@@ -0,0 +1,38 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::macros::MacroCall;
+use clippy_utils::source::expand_past_previous_comma;
+use clippy_utils::sym;
+use rustc_ast::{FormatArgs, FormatArgsPiece};
+use rustc_errors::Applicability;
+use rustc_lint::LateContext;
+
+use super::{PRINTLN_EMPTY_STRING, WRITELN_EMPTY_STRING};
+
+pub(super) fn check(cx: &LateContext<'_>, format_args: &FormatArgs, macro_call: &MacroCall, name: &str) {
+    if let [FormatArgsPiece::Literal(sym::LF)] = &format_args.template[..] {
+        let mut span = format_args.span;
+
+        let lint = if name == "writeln" {
+            span = expand_past_previous_comma(cx, span);
+
+            WRITELN_EMPTY_STRING
+        } else {
+            PRINTLN_EMPTY_STRING
+        };
+
+        span_lint_and_then(
+            cx,
+            lint,
+            macro_call.span,
+            format!("empty string literal in `{name}!`"),
+            |diag| {
+                diag.span_suggestion(
+                    span,
+                    "remove the empty string",
+                    String::new(),
+                    Applicability::MachineApplicable,
+                );
+            },
+        );
+    }
+}

clippy_lints/src/write/literal.rs

@@ -0,0 +1,285 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::macros::format_arg_removal_span;
+use clippy_utils::source::SpanRangeExt;
+use clippy_utils::sym;
+use rustc_ast::token::LitKind;
+use rustc_ast::{
+    FormatArgPosition, FormatArgPositionKind, FormatArgs, FormatArgsPiece, FormatCount, FormatOptions,
+    FormatPlaceholder, FormatTrait,
+};
+use rustc_errors::Applicability;
+use rustc_lint::LateContext;
+use rustc_span::Span;
+
+use super::{PRINT_LITERAL, WRITE_LITERAL};
+
+pub(super) fn check(cx: &LateContext<'_>, format_args: &FormatArgs, name: &str) {
+    let arg_index = |argument: &FormatArgPosition| argument.index.unwrap_or_else(|pos| pos);
+
+    let lint_name = if name.starts_with("write") {
+        WRITE_LITERAL
+    } else {
+        PRINT_LITERAL
+    };
+
+    let mut counts = vec![0u32; format_args.arguments.all_args().len()];
+    for piece in &format_args.template {
+        if let FormatArgsPiece::Placeholder(placeholder) = piece {
+            counts[arg_index(&placeholder.argument)] += 1;
+        }
+    }
+
+    let mut suggestion: Vec<(Span, String)> = vec![];
+    // holds index of replaced positional arguments; used to decrement the index of the remaining
+    // positional arguments.
+    let mut replaced_position: Vec<usize> = vec![];
+    let mut sug_span: Option<Span> = None;
+
+    for piece in &format_args.template {
+        if let FormatArgsPiece::Placeholder(FormatPlaceholder {
+            argument,
+            span: Some(placeholder_span),
+            format_trait: FormatTrait::Display,
+            format_options,
+        }) = piece
+            && *format_options == FormatOptions::default()
+            && let index = arg_index(argument)
+            && counts[index] == 1
+            && let Some(arg) = format_args.arguments.by_index(index)
+            && let rustc_ast::ExprKind::Lit(lit) = &arg.expr.kind
+            && !arg.expr.span.from_expansion()
+            && let Some(value_string) = arg.expr.span.get_source_text(cx)
+        {
+            let (replacement, replace_raw) = match lit.kind {
+                LitKind::Str | LitKind::StrRaw(_) => match extract_str_literal(&value_string) {
+                    Some(extracted) => extracted,
+                    None => return,
+                },
+                LitKind::Char => (
+                    match lit.symbol {
+                        sym::DOUBLE_QUOTE => "\\\"",
+                        sym::BACKSLASH_SINGLE_QUOTE => "'",
+                        _ => match value_string.strip_prefix('\'').and_then(|s| s.strip_suffix('\'')) {
+                            Some(stripped) => stripped,
+                            None => return,
+                        },
+                    }
+                    .to_string(),
+                    false,
+                ),
+                LitKind::Bool => (lit.symbol.to_string(), false),
+                _ => continue,
+            };
+
+            let Some(format_string_snippet) = format_args.span.get_source_text(cx) else {
+                continue;
+            };
+            let format_string_is_raw = format_string_snippet.starts_with('r');
+
+            let replacement = match (format_string_is_raw, replace_raw) {
+                (false, false) => Some(replacement),
+                (false, true) => Some(replacement.replace('\\', "\\\\").replace('"', "\\\"")),
+                (true, false) => match conservative_unescape(&replacement) {
+                    Ok(unescaped) => Some(unescaped),
+                    Err(UnescapeErr::Lint) => None,
+                    Err(UnescapeErr::Ignore) => continue,
+                },
+                (true, true) => {
+                    if replacement.contains(['#', '"']) {
+                        None
+                    } else {
+                        Some(replacement)
+                    }
+                },
+            };
+
+            sug_span = Some(sug_span.unwrap_or(arg.expr.span).to(arg.expr.span));
+
+            if let Some((_, index)) = format_arg_piece_span(piece) {
+                replaced_position.push(index);
+            }
+
+            if let Some(replacement) = replacement
+                // `format!("{}", "a")`, `format!("{named}", named = "b")
+                //              ~~~~~                      ~~~~~~~~~~~~~
+                && let Some(removal_span) = format_arg_removal_span(format_args, index)
+            {
+                let replacement = escape_braces(&replacement, !format_string_is_raw && !replace_raw);
+                suggestion.push((*placeholder_span, replacement));
+                suggestion.push((removal_span, String::new()));
+            }
+        }
+    }
+
+    // Decrement the index of the remaining by the number of replaced positional arguments
+    if !suggestion.is_empty() {
+        for piece in &format_args.template {
+            relocalize_format_args_indexes(piece, &mut suggestion, &replaced_position);
+        }
+    }
+
+    if let Some(span) = sug_span {
+        span_lint_and_then(cx, lint_name, span, "literal with an empty format string", |diag| {
+            if !suggestion.is_empty() {
+                diag.multipart_suggestion("try", suggestion, Applicability::MachineApplicable);
+            }
+        });
+    }
+}
+
+/// Extract Span and its index from the given `piece`
+fn format_arg_piece_span(piece: &FormatArgsPiece) -> Option<(Span, usize)> {
+    match piece {
+        FormatArgsPiece::Placeholder(FormatPlaceholder {
+            argument: FormatArgPosition { index: Ok(index), .. },
+            span: Some(span),
+            ..
+        }) => Some((*span, *index)),
+        _ => None,
+    }
+}
+
+/// Relocalizes the indexes of positional arguments in the format string
+fn relocalize_format_args_indexes(
+    piece: &FormatArgsPiece,
+    suggestion: &mut Vec<(Span, String)>,
+    replaced_position: &[usize],
+) {
+    if let FormatArgsPiece::Placeholder(FormatPlaceholder {
+        argument:
+            FormatArgPosition {
+                index: Ok(index),
+                // Only consider positional arguments
+                kind: FormatArgPositionKind::Number,
+                span: Some(span),
+            },
+        format_options,
+        ..
+    }) = piece
+    {
+        if suggestion.iter().any(|(s, _)| s.overlaps(*span)) {
+            // If the span is already in the suggestion, we don't need to process it again
+            return;
+        }
+
+        // lambda to get the decremented index based on the replaced positions
+        let decremented_index = |index: usize| -> usize {
+            let decrement = replaced_position.iter().filter(|&&i| i < index).count();
+            index - decrement
+        };
+
+        suggestion.push((*span, decremented_index(*index).to_string()));
+
+        // If there are format options, we need to handle them as well
+        if *format_options != FormatOptions::default() {
+            // lambda to process width and precision format counts and add them to the suggestion
+            let mut process_format_count = |count: &Option<FormatCount>, formatter: &dyn Fn(usize) -> String| {
+                if let Some(FormatCount::Argument(FormatArgPosition {
+                    index: Ok(format_arg_index),
+                    kind: FormatArgPositionKind::Number,
+                    span: Some(format_arg_span),
+                })) = count
+                {
+                    suggestion.push((*format_arg_span, formatter(decremented_index(*format_arg_index))));
+                }
+            };
+
+            process_format_count(&format_options.width, &|index: usize| format!("{index}$"));
+            process_format_count(&format_options.precision, &|index: usize| format!(".{index}$"));
+        }
+    }
+}
+
+/// Removes the raw marker, `#`s and quotes from a str, and returns if the literal is raw
+///
+/// `r#"a"#` -> (`a`, true)
+///
+/// `"b"` -> (`b`, false)
+fn extract_str_literal(literal: &str) -> Option<(String, bool)> {
+    let (literal, raw) = match literal.strip_prefix('r') {
+        Some(stripped) => (stripped.trim_matches('#'), true),
+        None => (literal, false),
+    };
+
+    Some((literal.strip_prefix('"')?.strip_suffix('"')?.to_string(), raw))
+}
+
+enum UnescapeErr {
+    /// Should still be linted, can be manually resolved by author, e.g.
+    ///
+    /// ```ignore
+    /// print!(r"{}", '"');
+    /// ```
+    Lint,
+    /// Should not be linted, e.g.
+    ///
+    /// ```ignore
+    /// print!(r"{}", '\r');
+    /// ```
+    Ignore,
+}
+
+/// Unescape a normal string into a raw string
+fn conservative_unescape(literal: &str) -> Result<String, UnescapeErr> {
+    let mut unescaped = String::with_capacity(literal.len());
+    let mut chars = literal.chars();
+    let mut err = false;
+
+    while let Some(ch) = chars.next() {
+        match ch {
+            '#' => err = true,
+            '\\' => match chars.next() {
+                Some('\\') => unescaped.push('\\'),
+                Some('"') => err = true,
+                _ => return Err(UnescapeErr::Ignore),
+            },
+            _ => unescaped.push(ch),
+        }
+    }
+
+    if err { Err(UnescapeErr::Lint) } else { Ok(unescaped) }
+}
+
+/// Replaces `{` with `{{` and `}` with `}}`. If `preserve_unicode_escapes` is `true` the braces
+/// in `\u{xxxx}` are left unmodified
+#[expect(clippy::match_same_arms)]
+fn escape_braces(literal: &str, preserve_unicode_escapes: bool) -> String {
+    #[derive(Clone, Copy)]
+    enum State {
+        Normal,
+        Backslash,
+        UnicodeEscape,
+    }
+
+    let mut escaped = String::with_capacity(literal.len());
+    let mut state = State::Normal;
+
+    for ch in literal.chars() {
+        state = match (ch, state) {
+            // Escape braces outside of unicode escapes by doubling them up
+            ('{' | '}', State::Normal) => {
+                escaped.push(ch);
+                State::Normal
+            },
+            // If `preserve_unicode_escapes` isn't enabled stay in `State::Normal`, otherwise:
+            //
+            // \u{aaaa} \\ \x01
+            // ^        ^  ^
+            ('\\', State::Normal) if preserve_unicode_escapes => State::Backslash,
+            // \u{aaaa}
+            //  ^
+            ('u', State::Backslash) => State::UnicodeEscape,
+            // \xAA \\
+            //  ^    ^
+            (_, State::Backslash) => State::Normal,
+            // \u{aaaa}
+            //        ^
+            ('}', State::UnicodeEscape) => State::Normal,
+            _ => state,
+        };
+
+        escaped.push(ch);
+    }
+
+    escaped
+}