src/tools/clippy/clippy_lints/src/write.rs

   1 use std::borrow::Cow;
   2 use std::iter;
   3 use std::ops::{Deref, Range};
   4
   5 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_and_then};
   6 use clippy_utils::source::{snippet, snippet_opt, snippet_with_applicability};
   7 use rustc_ast::ast::{Expr, ExprKind, Impl, Item, ItemKind, MacCall, Path, StrLit, StrStyle};
   8 use rustc_ast::ptr::P;
   9 use rustc_ast::token::{self, LitKind};
  10 use rustc_ast::tokenstream::TokenStream;
  11 use rustc_errors::{Applicability, DiagnosticBuilder};
  12 use rustc_lexer::unescape::{self, EscapeError};
  13 use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
  14 use rustc_parse::parser;
  15 use rustc_session::{declare_tool_lint, impl_lint_pass};
  16 use rustc_span::symbol::{kw, Symbol};
  17 use rustc_span::{sym, BytePos, InnerSpan, Span, DUMMY_SP};
  18
  19 declare_clippy_lint! {
  20     /// ### What it does
  21     /// This lint warns when you use `println!("")` to
  22     /// print a newline.
  23     ///
  24     /// ### Why is this bad?
  25     /// You should use `println!()`, which is simpler.
  26     ///
  27     /// ### Example
  28     /// ```rust
  29     /// println!("");
  30     /// ```
  31     ///
  32     /// Use instead:
  33     /// ```rust
  34     /// println!();
  35     /// ```
  36     #[clippy::version = "pre 1.29.0"]
  37     pub PRINTLN_EMPTY_STRING,
  38     style,
  39     "using `println!(\"\")` with an empty string"
  40 }
  41
  42 declare_clippy_lint! {
  43     /// ### What it does
  44     /// This lint warns when you use `print!()` with a format
  45     /// string that ends in a newline.
  46     ///
  47     /// ### Why is this bad?
  48     /// You should use `println!()` instead, which appends the
  49     /// newline.
  50     ///
  51     /// ### Example
  52     /// ```rust
  53     /// # let name = "World";
  54     /// print!("Hello {}!\n", name);
  55     /// ```
  56     /// use println!() instead
  57     /// ```rust
  58     /// # let name = "World";
  59     /// println!("Hello {}!", name);
  60     /// ```
  61     #[clippy::version = "pre 1.29.0"]
  62     pub PRINT_WITH_NEWLINE,
  63     style,
  64     "using `print!()` with a format string that ends in a single newline"
  65 }
  66
  67 declare_clippy_lint! {
  68     /// ### What it does
  69     /// Checks for printing on *stdout*. The purpose of this lint
  70     /// is to catch debugging remnants.
  71     ///
  72     /// ### Why is this bad?
  73     /// People often print on *stdout* while debugging an
  74     /// application and might forget to remove those prints afterward.
  75     ///
  76     /// ### Known problems
  77     /// * Only catches `print!` and `println!` calls.
  78     /// * The lint level is unaffected by crate attributes. The level can still
  79     ///   be set for functions, modules and other items. To change the level for
  80     ///   the entire crate, please use command line flags. More information and a
  81     ///   configuration example can be found in [clippy#6610].
  82     ///
  83     /// [clippy#6610]: https://github.com/rust-lang/rust-clippy/issues/6610#issuecomment-977120558
  84     ///
  85     /// ### Example
  86     /// ```rust
  87     /// println!("Hello world!");
  88     /// ```
  89     #[clippy::version = "pre 1.29.0"]
  90     pub PRINT_STDOUT,
  91     restriction,
  92     "printing on stdout"
  93 }
  94
  95 declare_clippy_lint! {
  96     /// ### What it does
  97     /// Checks for printing on *stderr*. The purpose of this lint
  98     /// is to catch debugging remnants.
  99     ///
 100     /// ### Why is this bad?
 101     /// People often print on *stderr* while debugging an
 102     /// application and might forget to remove those prints afterward.
 103     ///
 104     /// ### Known problems
 105     /// * Only catches `eprint!` and `eprintln!` calls.
 106     /// * The lint level is unaffected by crate attributes. The level can still
 107     ///   be set for functions, modules and other items. To change the level for
 108     ///   the entire crate, please use command line flags. More information and a
 109     ///   configuration example can be found in [clippy#6610].
 110     ///
 111     /// [clippy#6610]: https://github.com/rust-lang/rust-clippy/issues/6610#issuecomment-977120558
 112     ///
 113     /// ### Example
 114     /// ```rust
 115     /// eprintln!("Hello world!");
 116     /// ```
 117     #[clippy::version = "1.50.0"]
 118     pub PRINT_STDERR,
 119     restriction,
 120     "printing on stderr"
 121 }
 122
 123 declare_clippy_lint! {
 124     /// ### What it does
 125     /// Checks for use of `Debug` formatting. The purpose of this
 126     /// lint is to catch debugging remnants.
 127     ///
 128     /// ### Why is this bad?
 129     /// The purpose of the `Debug` trait is to facilitate
 130     /// debugging Rust code. It should not be used in user-facing output.
 131     ///
 132     /// ### Example
 133     /// ```rust
 134     /// # let foo = "bar";
 135     /// println!("{:?}", foo);
 136     /// ```
 137     #[clippy::version = "pre 1.29.0"]
 138     pub USE_DEBUG,
 139     restriction,
 140     "use of `Debug`-based formatting"
 141 }
 142
 143 declare_clippy_lint! {
 144     /// ### What it does
 145     /// This lint warns about the use of literals as `print!`/`println!` args.
 146     ///
 147     /// ### Why is this bad?
 148     /// Using literals as `println!` args is inefficient
 149     /// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
 150     /// (i.e., just put the literal in the format string)
 151     ///
 152     /// ### Known problems
 153     /// Will also warn with macro calls as arguments that expand to literals
 154     /// -- e.g., `println!("{}", env!("FOO"))`.
 155     ///
 156     /// ### Example
 157     /// ```rust
 158     /// println!("{}", "foo");
 159     /// ```
 160     /// use the literal without formatting:
 161     /// ```rust
 162     /// println!("foo");
 163     /// ```
 164     #[clippy::version = "pre 1.29.0"]
 165     pub PRINT_LITERAL,
 166     style,
 167     "printing a literal with a format string"
 168 }
 169
 170 declare_clippy_lint! {
 171     /// ### What it does
 172     /// This lint warns when you use `writeln!(buf, "")` to
 173     /// print a newline.
 174     ///
 175     /// ### Why is this bad?
 176     /// You should use `writeln!(buf)`, which is simpler.
 177     ///
 178     /// ### Example
 179     /// ```rust
 180     /// # use std::fmt::Write;
 181     /// # let mut buf = String::new();
 182     /// writeln!(buf, "");
 183     /// ```
 184     ///
 185     /// Use instead:
 186     /// ```rust
 187     /// # use std::fmt::Write;
 188     /// # let mut buf = String::new();
 189     /// writeln!(buf);
 190     /// ```
 191     #[clippy::version = "pre 1.29.0"]
 192     pub WRITELN_EMPTY_STRING,
 193     style,
 194     "using `writeln!(buf, \"\")` with an empty string"
 195 }
 196
 197 declare_clippy_lint! {
 198     /// ### What it does
 199     /// This lint warns when you use `write!()` with a format
 200     /// string that
 201     /// ends in a newline.
 202     ///
 203     /// ### Why is this bad?
 204     /// You should use `writeln!()` instead, which appends the
 205     /// newline.
 206     ///
 207     /// ### Example
 208     /// ```rust
 209     /// # use std::fmt::Write;
 210     /// # let mut buf = String::new();
 211     /// # let name = "World";
 212     /// write!(buf, "Hello {}!\n", name);
 213     /// ```
 214     ///
 215     /// Use instead:
 216     /// ```rust
 217     /// # use std::fmt::Write;
 218     /// # let mut buf = String::new();
 219     /// # let name = "World";
 220     /// writeln!(buf, "Hello {}!", name);
 221     /// ```
 222     #[clippy::version = "pre 1.29.0"]
 223     pub WRITE_WITH_NEWLINE,
 224     style,
 225     "using `write!()` with a format string that ends in a single newline"
 226 }
 227
 228 declare_clippy_lint! {
 229     /// ### What it does
 230     /// This lint warns about the use of literals as `write!`/`writeln!` args.
 231     ///
 232     /// ### Why is this bad?
 233     /// Using literals as `writeln!` args is inefficient
 234     /// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
 235     /// (i.e., just put the literal in the format string)
 236     ///
 237     /// ### Known problems
 238     /// Will also warn with macro calls as arguments that expand to literals
 239     /// -- e.g., `writeln!(buf, "{}", env!("FOO"))`.
 240     ///
 241     /// ### Example
 242     /// ```rust
 243     /// # use std::fmt::Write;
 244     /// # let mut buf = String::new();
 245     /// writeln!(buf, "{}", "foo");
 246     /// ```
 247     ///
 248     /// Use instead:
 249     /// ```rust
 250     /// # use std::fmt::Write;
 251     /// # let mut buf = String::new();
 252     /// writeln!(buf, "foo");
 253     /// ```
 254     #[clippy::version = "pre 1.29.0"]
 255     pub WRITE_LITERAL,
 256     style,
 257     "writing a literal with a format string"
 258 }
 259
 260 declare_clippy_lint! {
 261     /// ### What it does
 262     /// This lint warns when a named parameter in a format string is used as a positional one.
 263     ///
 264     /// ### Why is this bad?
 265     /// It may be confused for an assignment and obfuscates which parameter is being used.
 266     ///
 267     /// ### Example
 268     /// ```rust
 269     /// println!("{}", x = 10);
 270     /// ```
 271     ///
 272     /// Use instead:
 273     /// ```rust
 274     /// println!("{x}", x = 10);
 275     /// ```
 276     #[clippy::version = "1.63.0"]
 277     pub POSITIONAL_NAMED_FORMAT_PARAMETERS,
 278     suspicious,
 279     "named parameter in a format string is used positionally"
 280 }
 281
 282 #[derive(Default)]
 283 pub struct Write {
 284     in_debug_impl: bool,
 285 }
 286
 287 impl_lint_pass!(Write => [
 288     PRINT_WITH_NEWLINE,
 289     PRINTLN_EMPTY_STRING,
 290     PRINT_STDOUT,
 291     PRINT_STDERR,
 292     USE_DEBUG,
 293     PRINT_LITERAL,
 294     WRITE_WITH_NEWLINE,
 295     WRITELN_EMPTY_STRING,
 296     WRITE_LITERAL,
 297     POSITIONAL_NAMED_FORMAT_PARAMETERS,
 298 ]);
 299
 300 impl EarlyLintPass for Write {
 301     fn check_item(&mut self, _: &EarlyContext<'_>, item: &Item) {
 302         if let ItemKind::Impl(box Impl {
 303             of_trait: Some(trait_ref),
 304             ..
 305         }) = &item.kind
 306         {
 307             let trait_name = trait_ref
 308                 .path
 309                 .segments
 310                 .iter()
 311                 .last()
 312                 .expect("path has at least one segment")
 313                 .ident
 314                 .name;
 315             if trait_name == sym::Debug {
 316                 self.in_debug_impl = true;
 317             }
 318         }
 319     }
 320
 321     fn check_item_post(&mut self, _: &EarlyContext<'_>, _: &Item) {
 322         self.in_debug_impl = false;
 323     }
 324
 325     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &MacCall) {
 326         fn is_build_script(cx: &EarlyContext<'_>) -> bool {
 327             // Cargo sets the crate name for build scripts to `build_script_build`
 328             cx.sess()
 329                 .opts
 330                 .crate_name
 331                 .as_ref()
 332                 .map_or(false, |crate_name| crate_name == "build_script_build")
 333         }
 334
 335         if mac.path == sym!(print) {
 336             if !is_build_script(cx) {
 337                 span_lint(cx, PRINT_STDOUT, mac.span(), "use of `print!`");
 338             }
 339             self.lint_print_with_newline(cx, mac);
 340         } else if mac.path == sym!(println) {
 341             if !is_build_script(cx) {
 342                 span_lint(cx, PRINT_STDOUT, mac.span(), "use of `println!`");
 343             }
 344             self.lint_println_empty_string(cx, mac);
 345         } else if mac.path == sym!(eprint) {
 346             span_lint(cx, PRINT_STDERR, mac.span(), "use of `eprint!`");
 347             self.lint_print_with_newline(cx, mac);
 348         } else if mac.path == sym!(eprintln) {
 349             span_lint(cx, PRINT_STDERR, mac.span(), "use of `eprintln!`");
 350             self.lint_println_empty_string(cx, mac);
 351         } else if mac.path == sym!(write) {
 352             if let (Some(fmt_str), dest) = self.check_tts(cx, mac.args.inner_tokens(), true) {
 353                 if check_newlines(&fmt_str) {
 354                     let (nl_span, only_nl) = newline_span(&fmt_str);
 355                     let nl_span = match (dest, only_nl) {
 356                         // Special case of `write!(buf, "\n")`: Mark everything from the end of
 357                         // `buf` for removal so no trailing comma [`writeln!(buf, )`] remains.
 358                         (Some(dest_expr), true) => nl_span.with_lo(dest_expr.span.hi()),
 359                         _ => nl_span,
 360                     };
 361                     span_lint_and_then(
 362                         cx,
 363                         WRITE_WITH_NEWLINE,
 364                         mac.span(),
 365                         "using `write!()` with a format string that ends in a single newline",
 366                         |err| {
 367                             err.multipart_suggestion(
 368                                 "use `writeln!()` instead",
 369                                 vec![(mac.path.span, String::from("writeln")), (nl_span, String::new())],
 370                                 Applicability::MachineApplicable,
 371                             );
 372                         },
 373                     );
 374                 }
 375             }
 376         } else if mac.path == sym!(writeln) {
 377             if let (Some(fmt_str), expr) = self.check_tts(cx, mac.args.inner_tokens(), true) {
 378                 if fmt_str.symbol == kw::Empty {
 379                     let mut applicability = Applicability::MachineApplicable;
 380                     let suggestion = if let Some(e) = expr {
 381                         snippet_with_applicability(cx, e.span, "v", &mut applicability)
 382                     } else {
 383                         applicability = Applicability::HasPlaceholders;
 384                         Cow::Borrowed("v")
 385                     };
 386
 387                     span_lint_and_sugg(
 388                         cx,
 389                         WRITELN_EMPTY_STRING,
 390                         mac.span(),
 391                         format!("using `writeln!({}, \"\")`", suggestion).as_str(),
 392                         "replace it with",
 393                         format!("writeln!({})", suggestion),
 394                         applicability,
 395                     );
 396                 }
 397             }
 398         }
 399     }
 400 }
 401
 402 /// Given a format string that ends in a newline and its span, calculates the span of the
 403 /// newline, or the format string itself if the format string consists solely of a newline.
 404 /// Return this and a boolean indicating whether it only consisted of a newline.
 405 fn newline_span(fmtstr: &StrLit) -> (Span, bool) {
 406     let sp = fmtstr.span;
 407     let contents = fmtstr.symbol.as_str();
 408
 409     if contents == r"\n" {
 410         return (sp, true);
 411     }
 412
 413     let newline_sp_hi = sp.hi()
 414         - match fmtstr.style {
 415             StrStyle::Cooked => BytePos(1),
 416             StrStyle::Raw(hashes) => BytePos((1 + hashes).into()),
 417         };
 418
 419     let newline_sp_len = if contents.ends_with('\n') {
 420         BytePos(1)
 421     } else if contents.ends_with(r"\n") {
 422         BytePos(2)
 423     } else {
 424         panic!("expected format string to contain a newline");
 425     };
 426
 427     (sp.with_lo(newline_sp_hi - newline_sp_len).with_hi(newline_sp_hi), false)
 428 }
 429
 430 /// Stores a list of replacement spans for each argument, but only if all the replacements used an
 431 /// empty format string.
 432 #[derive(Default)]
 433 struct SimpleFormatArgs {
 434     unnamed: Vec<Vec<Span>>,
 435     complex_unnamed: Vec<Vec<Span>>,
 436     named: Vec<(Symbol, Vec<Span>)>,
 437 }
 438 impl SimpleFormatArgs {
 439     fn get_unnamed(&self) -> impl Iterator<Item = &[Span]> {
 440         self.unnamed.iter().map(|x| match x.as_slice() {
 441             // Ignore the dummy span added from out of order format arguments.
 442             [DUMMY_SP] => &[],
 443             x => x,
 444         })
 445     }
 446
 447     fn get_complex_unnamed(&self) -> impl Iterator<Item = &[Span]> {
 448         self.complex_unnamed.iter().map(Vec::as_slice)
 449     }
 450
 451     fn get_named(&self, n: &Path) -> &[Span] {
 452         self.named.iter().find(|x| *n == x.0).map_or(&[], |x| x.1.as_slice())
 453     }
 454
 455     fn push(&mut self, arg: rustc_parse_format::Argument<'_>, span: Span) {
 456         use rustc_parse_format::{
 457             AlignUnknown, ArgumentImplicitlyIs, ArgumentIs, ArgumentNamed, CountImplied, FormatSpec,
 458         };
 459
 460         const SIMPLE: FormatSpec<'_> = FormatSpec {
 461             fill: None,
 462             align: AlignUnknown,
 463             flags: 0,
 464             precision: CountImplied,
 465             precision_span: None,
 466             width: CountImplied,
 467             width_span: None,
 468             ty: "",
 469             ty_span: None,
 470         };
 471
 472         match arg.position {
 473             ArgumentIs(n) | ArgumentImplicitlyIs(n) => {
 474                 if self.unnamed.len() <= n {
 475                     // Use a dummy span to mark all unseen arguments.
 476                     self.unnamed.resize_with(n, || vec![DUMMY_SP]);
 477                     if arg.format == SIMPLE {
 478                         self.unnamed.push(vec![span]);
 479                     } else {
 480                         self.unnamed.push(Vec::new());
 481                     }
 482                 } else {
 483                     let args = &mut self.unnamed[n];
 484                     match (args.as_mut_slice(), arg.format == SIMPLE) {
 485                         // A non-empty format string has been seen already.
 486                         ([], _) => (),
 487                         // Replace the dummy span, if it exists.
 488                         ([dummy @ DUMMY_SP], true) => *dummy = span,
 489                         ([_, ..], true) => args.push(span),
 490                         ([_, ..], false) => *args = Vec::new(),
 491                     }
 492                 }
 493             },
 494             ArgumentNamed(n) => {
 495                 let n = Symbol::intern(n);
 496                 if let Some(x) = self.named.iter_mut().find(|x| x.0 == n) {
 497                     match x.1.as_slice() {
 498                         // A non-empty format string has been seen already.
 499                         [] => (),
 500                         [_, ..] if arg.format == SIMPLE => x.1.push(span),
 501                         [_, ..] => x.1 = Vec::new(),
 502                     }
 503                 } else if arg.format == SIMPLE {
 504                     self.named.push((n, vec![span]));
 505                 } else {
 506                     self.named.push((n, Vec::new()));
 507                 }
 508             },
 509         };
 510     }
 511
 512     fn push_to_complex(&mut self, span: Span, position: usize) {
 513         if self.complex_unnamed.len() <= position {
 514             self.complex_unnamed.resize_with(position, Vec::new);
 515             self.complex_unnamed.push(vec![span]);
 516         } else {
 517             let args: &mut Vec<Span> = &mut self.complex_unnamed[position];
 518             args.push(span);
 519         }
 520     }
 521
 522     fn push_complex(
 523         &mut self,
 524         cx: &EarlyContext<'_>,
 525         arg: rustc_parse_format::Argument<'_>,
 526         str_lit_span: Span,
 527         fmt_span: Span,
 528     ) {
 529         use rustc_parse_format::{ArgumentImplicitlyIs, ArgumentIs, CountIsParam, CountIsStar};
 530
 531         let snippet = snippet_opt(cx, fmt_span);
 532
 533         let end = snippet
 534             .as_ref()
 535             .and_then(|s| s.find(':'))
 536             .or_else(|| fmt_span.hi().0.checked_sub(fmt_span.lo().0 + 1).map(|u| u as usize));
 537
 538         if let (ArgumentIs(n) | ArgumentImplicitlyIs(n), Some(end)) = (arg.position, end) {
 539             let span = fmt_span.from_inner(InnerSpan::new(1, end));
 540             self.push_to_complex(span, n);
 541         };
 542
 543         if let (CountIsParam(n) | CountIsStar(n), Some(span)) = (arg.format.precision, arg.format.precision_span) {
 544             // We need to do this hack as precision spans should be converted from .* to .foo$
 545             let hack = if snippet.as_ref().and_then(|s| s.find('*')).is_some() {
 546                 0
 547             } else {
 548                 1
 549             };
 550
 551             let span = str_lit_span.from_inner(InnerSpan {
 552                 start: span.start + 1,
 553                 end: span.end - hack,
 554             });
 555             self.push_to_complex(span, n);
 556         };
 557
 558         if let (CountIsParam(n), Some(span)) = (arg.format.width, arg.format.width_span) {
 559             let span = str_lit_span.from_inner(InnerSpan {
 560                 start: span.start,
 561                 end: span.end - 1,
 562             });
 563             self.push_to_complex(span, n);
 564         };
 565     }
 566 }
 567
 568 impl Write {
 569     /// Parses a format string into a collection of spans for each argument. This only keeps track
 570     /// of empty format arguments. Will also lint usages of debug format strings outside of debug
 571     /// impls.
 572     fn parse_fmt_string(&self, cx: &EarlyContext<'_>, str_lit: &StrLit) -> Option<SimpleFormatArgs> {
 573         use rustc_parse_format::{ParseMode, Parser, Piece};
 574
 575         let str_sym = str_lit.symbol_unescaped.as_str();
 576         let style = match str_lit.style {
 577             StrStyle::Cooked => None,
 578             StrStyle::Raw(n) => Some(n as usize),
 579         };
 580
 581         let mut parser = Parser::new(str_sym, style, snippet_opt(cx, str_lit.span), false, ParseMode::Format);
 582         let mut args = SimpleFormatArgs::default();
 583
 584         while let Some(arg) = parser.next() {
 585             let arg = match arg {
 586                 Piece::String(_) => continue,
 587                 Piece::NextArgument(arg) => arg,
 588             };
 589             let span = parser
 590                 .arg_places
 591                 .last()
 592                 .map_or(DUMMY_SP, |&x| str_lit.span.from_inner(InnerSpan::new(x.start, x.end)));
 593
 594             if !self.in_debug_impl && arg.format.ty == "?" {
 595                 // FIXME: modify rustc's fmt string parser to give us the current span
 596                 span_lint(cx, USE_DEBUG, span, "use of `Debug`-based formatting");
 597             }
 598             args.push(arg, span);
 599             args.push_complex(cx, arg, str_lit.span, span);
 600         }
 601
 602         parser.errors.is_empty().then_some(args)
 603     }
 604
 605     /// Checks the arguments of `print[ln]!` and `write[ln]!` calls. It will return a tuple of two
 606     /// `Option`s. The first `Option` of the tuple is the macro's format string. It includes
 607     /// the contents of the string, whether it's a raw string, and the span of the literal in the
 608     /// source. The second `Option` in the tuple is, in the `write[ln]!` case, the expression the
 609     /// `format_str` should be written to.
 610     ///
 611     /// Example:
 612     ///
 613     /// Calling this function on
 614     /// ```rust
 615     /// # use std::fmt::Write;
 616     /// # let mut buf = String::new();
 617     /// # let something = "something";
 618     /// writeln!(buf, "string to write: {}", something);
 619     /// ```
 620     /// will return
 621     /// ```rust,ignore
 622     /// (Some("string to write: {}"), Some(buf))
 623     /// ```
 624     fn check_tts<'a>(&self, cx: &EarlyContext<'a>, tts: TokenStream, is_write: bool) -> (Option<StrLit>, Option<Expr>) {
 625         let mut parser = parser::Parser::new(&cx.sess().parse_sess, tts, false, None);
 626         let expr = if is_write {
 627             match parser
 628                 .parse_expr()
 629                 .map(rustc_ast::ptr::P::into_inner)
 630                 .map_err(DiagnosticBuilder::cancel)
 631             {
 632                 // write!(e, ...)
 633                 Ok(p) if parser.eat(&token::Comma) => Some(p),
 634                 // write!(e) or error
 635                 e => return (None, e.ok()),
 636             }
 637         } else {
 638             None
 639         };
 640
 641         let fmtstr = match parser.parse_str_lit() {
 642             Ok(fmtstr) => fmtstr,
 643             Err(_) => return (None, expr),
 644         };
 645
 646         let args = match self.parse_fmt_string(cx, &fmtstr) {
 647             Some(args) => args,
 648             None => return (Some(fmtstr), expr),
 649         };
 650
 651         let lint = if is_write { WRITE_LITERAL } else { PRINT_LITERAL };
 652         let mut unnamed_args = args.get_unnamed();
 653         let mut complex_unnamed_args = args.get_complex_unnamed();
 654         loop {
 655             if !parser.eat(&token::Comma) {
 656                 return (Some(fmtstr), expr);
 657             }
 658
 659             let comma_span = parser.prev_token.span;
 660             let token_expr = if let Ok(expr) = parser.parse_expr().map_err(DiagnosticBuilder::cancel) {
 661                 expr
 662             } else {
 663                 return (Some(fmtstr), None);
 664             };
 665             let complex_unnamed_arg = complex_unnamed_args.next();
 666
 667             let (fmt_spans, lit) = match &token_expr.kind {
 668                 ExprKind::Lit(lit) => (unnamed_args.next().unwrap_or(&[]), lit),
 669                 ExprKind::Assign(lhs, rhs, _) => {
 670                     if let Some(span) = complex_unnamed_arg {
 671                         for x in span {
 672                             Self::report_positional_named_param(cx, *x, lhs, rhs);
 673                         }
 674                     }
 675                     match (&lhs.kind, &rhs.kind) {
 676                         (ExprKind::Path(_, p), ExprKind::Lit(lit)) => (args.get_named(p), lit),
 677                         _ => continue,
 678                     }
 679                 },
 680                 _ => {
 681                     unnamed_args.next();
 682                     continue;
 683                 },
 684             };
 685
 686             let replacement: String = match lit.token_lit.kind {
 687                 LitKind::StrRaw(_) | LitKind::ByteStrRaw(_) if matches!(fmtstr.style, StrStyle::Raw(_)) => {
 688                     lit.token_lit.symbol.as_str().replace('{', "{{").replace('}', "}}")
 689                 },
 690                 LitKind::Str | LitKind::ByteStr if matches!(fmtstr.style, StrStyle::Cooked) => {
 691                     lit.token_lit.symbol.as_str().replace('{', "{{").replace('}', "}}")
 692                 },
 693                 LitKind::StrRaw(_)
 694                 | LitKind::Str
 695                 | LitKind::ByteStrRaw(_)
 696                 | LitKind::ByteStr
 697                 | LitKind::Integer
 698                 | LitKind::Float
 699                 | LitKind::Err => continue,
 700                 LitKind::Byte | LitKind::Char => match lit.token_lit.symbol.as_str() {
 701                     "\"" if matches!(fmtstr.style, StrStyle::Cooked) => "\\\"",
 702                     "\"" if matches!(fmtstr.style, StrStyle::Raw(0)) => continue,
 703                     "\\\\" if matches!(fmtstr.style, StrStyle::Raw(_)) => "\\",
 704                     "\\'" => "'",
 705                     "{" => "{{",
 706                     "}" => "}}",
 707                     x if matches!(fmtstr.style, StrStyle::Raw(_)) && x.starts_with('\\') => continue,
 708                     x => x,
 709                 }
 710                 .into(),
 711                 LitKind::Bool => lit.token_lit.symbol.as_str().deref().into(),
 712             };
 713
 714             if !fmt_spans.is_empty() {
 715                 span_lint_and_then(
 716                     cx,
 717                     lint,
 718                     token_expr.span,
 719                     "literal with an empty format string",
 720                     |diag| {
 721                         diag.multipart_suggestion(
 722                             "try this",
 723                             iter::once((comma_span.to(token_expr.span), String::new()))
 724                                 .chain(fmt_spans.iter().copied().zip(iter::repeat(replacement)))
 725                                 .collect(),
 726                             Applicability::MachineApplicable,
 727                         );
 728                     },
 729                 );
 730             }
 731         }
 732     }
 733
 734     fn report_positional_named_param(cx: &EarlyContext<'_>, span: Span, lhs: &P<Expr>, _rhs: &P<Expr>) {
 735         if let ExprKind::Path(_, _p) = &lhs.kind {
 736             let mut applicability = Applicability::MachineApplicable;
 737             let name = snippet_with_applicability(cx, lhs.span, "name", &mut applicability);
 738             // We need to do this hack as precision spans should be converted from .* to .foo$
 739             let hack = snippet(cx, span, "").contains('*');
 740
 741             span_lint_and_sugg(
 742                 cx,
 743                 POSITIONAL_NAMED_FORMAT_PARAMETERS,
 744                 span,
 745                 &format!("named parameter {} is used as a positional parameter", name),
 746                 "replace it with",
 747                 if hack {
 748                     format!("{}$", name)
 749                 } else {
 750                     format!("{}", name)
 751                 },
 752                 applicability,
 753             );
 754         };
 755     }
 756
 757     fn lint_println_empty_string(&self, cx: &EarlyContext<'_>, mac: &MacCall) {
 758         if let (Some(fmt_str), _) = self.check_tts(cx, mac.args.inner_tokens(), false) {
 759             if fmt_str.symbol == kw::Empty {
 760                 let name = mac.path.segments[0].ident.name;
 761                 span_lint_and_sugg(
 762                     cx,
 763                     PRINTLN_EMPTY_STRING,
 764                     mac.span(),
 765                     &format!("using `{}!(\"\")`", name),
 766                     "replace it with",
 767                     format!("{}!()", name),
 768                     Applicability::MachineApplicable,
 769                 );
 770             }
 771         }
 772     }
 773
 774     fn lint_print_with_newline(&self, cx: &EarlyContext<'_>, mac: &MacCall) {
 775         if let (Some(fmt_str), _) = self.check_tts(cx, mac.args.inner_tokens(), false) {
 776             if check_newlines(&fmt_str) {
 777                 let name = mac.path.segments[0].ident.name;
 778                 let suggested = format!("{}ln", name);
 779                 span_lint_and_then(
 780                     cx,
 781                     PRINT_WITH_NEWLINE,
 782                     mac.span(),
 783                     &format!("using `{}!()` with a format string that ends in a single newline", name),
 784                     |err| {
 785                         err.multipart_suggestion(
 786                             &format!("use `{}!` instead", suggested),
 787                             vec![(mac.path.span, suggested), (newline_span(&fmt_str).0, String::new())],
 788                             Applicability::MachineApplicable,
 789                         );
 790                     },
 791                 );
 792             }
 793         }
 794     }
 795 }
 796
 797 /// Checks if the format string contains a single newline that terminates it.
 798 ///
 799 /// Literal and escaped newlines are both checked (only literal for raw strings).
 800 fn check_newlines(fmtstr: &StrLit) -> bool {
 801     let mut has_internal_newline = false;
 802     let mut last_was_cr = false;
 803     let mut should_lint = false;
 804
 805     let contents = fmtstr.symbol.as_str();
 806
 807     let mut cb = |r: Range<usize>, c: Result<char, EscapeError>| {
 808         let c = match c {
 809             Ok(c) => c,
 810             Err(e) if !e.is_fatal() => return,
 811             Err(e) => panic!("{:?}", e),
 812         };
 813
 814         if r.end == contents.len() && c == '\n' && !last_was_cr && !has_internal_newline {
 815             should_lint = true;
 816         } else {
 817             last_was_cr = c == '\r';
 818             if c == '\n' {
 819                 has_internal_newline = true;
 820             }
 821         }
 822     };
 823
 824     match fmtstr.style {
 825         StrStyle::Cooked => unescape::unescape_literal(contents, unescape::Mode::Str, &mut cb),
 826         StrStyle::Raw(_) => unescape::unescape_literal(contents, unescape::Mode::RawStr, &mut cb),
 827     }
 828
 829     should_lint
 830 }