4 use crate::utils::{snippet_with_applicability, span_lint, span_lint_and_sugg, span_lint_and_then};
5 use rustc_ast::ast::{Expr, ExprKind, Item, ItemKind, MacCall, StrLit, StrStyle};
7 use rustc_ast::tokenstream::TokenStream;
8 use rustc_errors::Applicability;
9 use rustc_lexer::unescape::{self, EscapeError};
10 use rustc_lint::{EarlyContext, EarlyLintPass};
11 use rustc_parse::parser;
12 use rustc_session::{declare_tool_lint, impl_lint_pass};
13 use rustc_span::symbol::kw;
14 use rustc_span::{sym, BytePos, Span};
16 declare_clippy_lint! {
17 /// **What it does:** This lint warns when you use `println!("")` to
20 /// **Why is this bad?** You should use `println!()`, which is simpler.
22 /// **Known problems:** None.
32 pub PRINTLN_EMPTY_STRING,
34 "using `println!(\"\")` with an empty string"
37 declare_clippy_lint! {
38 /// **What it does:** This lint warns when you use `print!()` with a format
39 /// string that ends in a newline.
41 /// **Why is this bad?** You should use `println!()` instead, which appends the
44 /// **Known problems:** None.
48 /// # let name = "World";
49 /// print!("Hello {}!\n", name);
51 /// use println!() instead
53 /// # let name = "World";
54 /// println!("Hello {}!", name);
56 pub PRINT_WITH_NEWLINE,
58 "using `print!()` with a format string that ends in a single newline"
61 declare_clippy_lint! {
62 /// **What it does:** Checks for printing on *stdout*. The purpose of this lint
63 /// is to catch debugging remnants.
65 /// **Why is this bad?** People often print on *stdout* while debugging an
66 /// application and might forget to remove those prints afterward.
68 /// **Known problems:** Only catches `print!` and `println!` calls.
72 /// println!("Hello world!");
79 declare_clippy_lint! {
80 /// **What it does:** Checks for printing on *stderr*. The purpose of this lint
81 /// is to catch debugging remnants.
83 /// **Why is this bad?** People often print on *stderr* while debugging an
84 /// application and might forget to remove those prints afterward.
86 /// **Known problems:** Only catches `eprint!` and `eprintln!` calls.
90 /// eprintln!("Hello world!");
97 declare_clippy_lint! {
98 /// **What it does:** Checks for use of `Debug` formatting. The purpose of this
99 /// lint is to catch debugging remnants.
101 /// **Why is this bad?** The purpose of the `Debug` trait is to facilitate
102 /// debugging Rust code. It should not be used in user-facing output.
106 /// # let foo = "bar";
107 /// println!("{:?}", foo);
111 "use of `Debug`-based formatting"
114 declare_clippy_lint! {
115 /// **What it does:** This lint warns about the use of literals as `print!`/`println!` args.
117 /// **Why is this bad?** Using literals as `println!` args is inefficient
118 /// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
119 /// (i.e., just put the literal in the format string)
121 /// **Known problems:** Will also warn with macro calls as arguments that expand to literals
122 /// -- e.g., `println!("{}", env!("FOO"))`.
126 /// println!("{}", "foo");
128 /// use the literal without formatting:
134 "printing a literal with a format string"
137 declare_clippy_lint! {
138 /// **What it does:** This lint warns when you use `writeln!(buf, "")` to
141 /// **Why is this bad?** You should use `writeln!(buf)`, which is simpler.
143 /// **Known problems:** None.
147 /// # use std::fmt::Write;
148 /// # let mut buf = String::new();
151 /// writeln!(buf, "");
156 pub WRITELN_EMPTY_STRING,
158 "using `writeln!(buf, \"\")` with an empty string"
161 declare_clippy_lint! {
162 /// **What it does:** This lint warns when you use `write!()` with a format
164 /// ends in a newline.
166 /// **Why is this bad?** You should use `writeln!()` instead, which appends the
169 /// **Known problems:** None.
173 /// # use std::fmt::Write;
174 /// # let mut buf = String::new();
175 /// # let name = "World";
178 /// write!(buf, "Hello {}!\n", name);
181 /// writeln!(buf, "Hello {}!", name);
183 pub WRITE_WITH_NEWLINE,
185 "using `write!()` with a format string that ends in a single newline"
188 declare_clippy_lint! {
189 /// **What it does:** This lint warns about the use of literals as `write!`/`writeln!` args.
191 /// **Why is this bad?** Using literals as `writeln!` args is inefficient
192 /// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
193 /// (i.e., just put the literal in the format string)
195 /// **Known problems:** Will also warn with macro calls as arguments that expand to literals
196 /// -- e.g., `writeln!(buf, "{}", env!("FOO"))`.
200 /// # use std::fmt::Write;
201 /// # let mut buf = String::new();
204 /// writeln!(buf, "{}", "foo");
207 /// writeln!(buf, "foo");
211 "writing a literal with a format string"
219 impl_lint_pass!(Write => [
221 PRINTLN_EMPTY_STRING,
227 WRITELN_EMPTY_STRING,
231 impl EarlyLintPass for Write {
232 fn check_item(&mut self, _: &EarlyContext<'_>, item: &Item) {
233 if let ItemKind::Impl {
234 of_trait: Some(trait_ref),
238 let trait_name = trait_ref
243 .expect("path has at least one segment")
246 if trait_name == sym::Debug {
247 self.in_debug_impl = true;
252 fn check_item_post(&mut self, _: &EarlyContext<'_>, _: &Item) {
253 self.in_debug_impl = false;
256 fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &MacCall) {
257 fn is_build_script(cx: &EarlyContext<'_>) -> bool {
258 // Cargo sets the crate name for build scripts to `build_script_build`
263 .map_or(false, |crate_name| crate_name == "build_script_build")
266 if mac.path == sym!(print) {
267 if !is_build_script(cx) {
268 span_lint(cx, PRINT_STDOUT, mac.span(), "use of `print!`");
270 self.lint_print_with_newline(cx, mac);
271 } else if mac.path == sym!(println) {
272 if !is_build_script(cx) {
273 span_lint(cx, PRINT_STDOUT, mac.span(), "use of `println!`");
275 self.lint_println_empty_string(cx, mac);
276 } else if mac.path == sym!(eprint) {
277 span_lint(cx, PRINT_STDERR, mac.span(), "use of `eprint!`");
278 self.lint_print_with_newline(cx, mac);
279 } else if mac.path == sym!(eprintln) {
280 span_lint(cx, PRINT_STDERR, mac.span(), "use of `eprintln!`");
281 self.lint_println_empty_string(cx, mac);
282 } else if mac.path == sym!(write) {
283 if let (Some(fmt_str), _) = self.check_tts(cx, mac.args.inner_tokens(), true) {
284 if check_newlines(&fmt_str) {
289 "using `write!()` with a format string that ends in a single newline",
291 err.multipart_suggestion(
292 "use `writeln!()` instead",
294 (mac.path.span, String::from("writeln")),
295 (newline_span(&fmt_str), String::new()),
297 Applicability::MachineApplicable,
303 } else if mac.path == sym!(writeln) {
304 if let (Some(fmt_str), expr) = self.check_tts(cx, mac.args.inner_tokens(), true) {
305 if fmt_str.symbol == kw::Empty {
306 let mut applicability = Applicability::MachineApplicable;
307 // FIXME: remove this `#[allow(...)]` once the issue #5822 gets fixed
308 #[allow(clippy::option_if_let_else)]
309 let suggestion = if let Some(e) = expr {
310 snippet_with_applicability(cx, e.span, "v", &mut applicability)
312 applicability = Applicability::HasPlaceholders;
318 WRITELN_EMPTY_STRING,
320 format!("using `writeln!({}, \"\")`", suggestion).as_str(),
322 format!("writeln!({})", suggestion),
331 /// Given a format string that ends in a newline and its span, calculates the span of the
332 /// newline, or the format string itself if the format string consists solely of a newline.
333 fn newline_span(fmtstr: &StrLit) -> Span {
334 let sp = fmtstr.span;
335 let contents = &fmtstr.symbol.as_str();
337 if *contents == r"\n" {
341 let newline_sp_hi = sp.hi()
342 - match fmtstr.style {
343 StrStyle::Cooked => BytePos(1),
344 StrStyle::Raw(hashes) => BytePos((1 + hashes).into()),
347 let newline_sp_len = if contents.ends_with('\n') {
349 } else if contents.ends_with(r"\n") {
352 panic!("expected format string to contain a newline");
355 sp.with_lo(newline_sp_hi - newline_sp_len).with_hi(newline_sp_hi)
359 /// Checks the arguments of `print[ln]!` and `write[ln]!` calls. It will return a tuple of two
360 /// `Option`s. The first `Option` of the tuple is the macro's format string. It includes
361 /// the contents of the string, whether it's a raw string, and the span of the literal in the
362 /// source. The second `Option` in the tuple is, in the `write[ln]!` case, the expression the
363 /// `format_str` should be written to.
367 /// Calling this function on
369 /// # use std::fmt::Write;
370 /// # let mut buf = String::new();
371 /// # let something = "something";
372 /// writeln!(buf, "string to write: {}", something);
376 /// (Some("string to write: {}"), Some(buf))
378 #[allow(clippy::too_many_lines)]
379 fn check_tts<'a>(&self, cx: &EarlyContext<'a>, tts: TokenStream, is_write: bool) -> (Option<StrLit>, Option<Expr>) {
380 use rustc_parse_format::{
381 AlignUnknown, ArgumentImplicitlyIs, ArgumentIs, ArgumentNamed, CountImplied, FormatSpec, ParseMode, Parser,
385 let mut parser = parser::Parser::new(&cx.sess.parse_sess, tts, false, None);
386 let mut expr: Option<Expr> = None;
388 expr = match parser.parse_expr().map_err(|mut err| err.cancel()) {
389 Ok(p) => Some(p.into_inner()),
390 Err(_) => return (None, None),
392 // might be `writeln!(foo)`
393 if parser.expect(&token::Comma).map_err(|mut err| err.cancel()).is_err() {
398 let fmtstr = match parser.parse_str_lit() {
399 Ok(fmtstr) => fmtstr,
400 Err(_) => return (None, expr),
402 let tmp = fmtstr.symbol.as_str();
403 let mut args = vec![];
404 let mut fmt_parser = Parser::new(&tmp, None, None, false, ParseMode::Format);
405 while let Some(piece) = fmt_parser.next() {
406 if !fmt_parser.errors.is_empty() {
409 if let Piece::NextArgument(arg) = piece {
410 if !self.in_debug_impl && arg.format.ty == "?" {
411 // FIXME: modify rustc's fmt string parser to give us the current span
412 span_lint(cx, USE_DEBUG, parser.prev_token.span, "use of `Debug`-based formatting");
417 let lint = if is_write { WRITE_LITERAL } else { PRINT_LITERAL };
420 const SIMPLE: FormatSpec<'_> = FormatSpec {
424 precision: CountImplied,
425 precision_span: None,
431 if !parser.eat(&token::Comma) {
432 return (Some(fmtstr), expr);
434 let token_expr = if let Ok(expr) = parser.parse_expr().map_err(|mut err| err.cancel()) {
437 return (Some(fmtstr), None);
439 match &token_expr.kind {
440 ExprKind::Lit(_) => {
441 let mut all_simple = true;
442 let mut seen = false;
445 ArgumentImplicitlyIs(n) | ArgumentIs(n) => {
447 all_simple &= arg.format == SIMPLE;
451 ArgumentNamed(_) => {},
454 if all_simple && seen {
455 span_lint(cx, lint, token_expr.span, "literal with an empty format string");
459 ExprKind::Assign(lhs, rhs, _) => {
460 if let ExprKind::Lit(_) = rhs.kind {
461 if let ExprKind::Path(_, p) = &lhs.kind {
462 let mut all_simple = true;
463 let mut seen = false;
466 ArgumentImplicitlyIs(_) | ArgumentIs(_) => {},
467 ArgumentNamed(name) => {
470 all_simple &= arg.format == SIMPLE;
475 if all_simple && seen {
476 span_lint(cx, lint, rhs.span, "literal with an empty format string");
486 fn lint_println_empty_string(&self, cx: &EarlyContext<'_>, mac: &MacCall) {
487 if let (Some(fmt_str), _) = self.check_tts(cx, mac.args.inner_tokens(), false) {
488 if fmt_str.symbol == kw::Empty {
489 let name = mac.path.segments[0].ident.name;
492 PRINTLN_EMPTY_STRING,
494 &format!("using `{}!(\"\")`", name),
496 format!("{}!()", name),
497 Applicability::MachineApplicable,
503 fn lint_print_with_newline(&self, cx: &EarlyContext<'_>, mac: &MacCall) {
504 if let (Some(fmt_str), _) = self.check_tts(cx, mac.args.inner_tokens(), false) {
505 if check_newlines(&fmt_str) {
506 let name = mac.path.segments[0].ident.name;
507 let suggested = format!("{}ln", name);
512 &format!("using `{}!()` with a format string that ends in a single newline", name),
514 err.multipart_suggestion(
515 &format!("use `{}!` instead", suggested),
516 vec![(mac.path.span, suggested), (newline_span(&fmt_str), String::new())],
517 Applicability::MachineApplicable,
526 /// Checks if the format string contains a single newline that terminates it.
528 /// Literal and escaped newlines are both checked (only literal for raw strings).
529 fn check_newlines(fmtstr: &StrLit) -> bool {
530 let mut has_internal_newline = false;
531 let mut last_was_cr = false;
532 let mut should_lint = false;
534 let contents = &fmtstr.symbol.as_str();
536 let mut cb = |r: Range<usize>, c: Result<char, EscapeError>| {
539 if r.end == contents.len() && c == '\n' && !last_was_cr && !has_internal_newline {
542 last_was_cr = c == '\r';
544 has_internal_newline = true;
550 StrStyle::Cooked => unescape::unescape_literal(contents, unescape::Mode::Str, &mut cb),
551 StrStyle::Raw(_) => unescape::unescape_literal(contents, unescape::Mode::RawStr, &mut cb),