rust-clippy/clippy_lints/src/write.rs

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use std::borrow::Cow;
use std::ops::Range;
use crate::utils::{span_lint, span_lint_and_sugg, span_lint_and_then};
use clippy_utils::source::snippet_with_applicability;
use if_chain::if_chain;
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use rustc_ast::ast::{Expr, ExprKind, ImplKind, Item, ItemKind, LitKind, MacCall, StrLit, StrStyle};
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use rustc_ast::token;
use rustc_ast::tokenstream::TokenStream;
use rustc_errors::Applicability;
use rustc_lexer::unescape::{self, EscapeError};
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use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_parse::parser;
use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::symbol::kw;
use rustc_span::{sym, BytePos, Span};
declare_clippy_lint! {
/// **What it does:** This lint warns when you use `println!("")` to
/// print a newline.
///
/// **Why is this bad?** You should use `println!()`, which is simpler.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
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/// // Bad
/// println!("");
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///
/// // Good
/// println!();
/// ```
pub PRINTLN_EMPTY_STRING,
style,
"using `println!(\"\")` with an empty string"
}
declare_clippy_lint! {
/// **What it does:** This lint warns when you use `print!()` with a format
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/// string that ends in a newline.
///
/// **Why is this bad?** You should use `println!()` instead, which appends the
/// newline.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # let name = "World";
/// print!("Hello {}!\n", name);
/// ```
/// use println!() instead
/// ```rust
/// # let name = "World";
/// println!("Hello {}!", name);
/// ```
pub PRINT_WITH_NEWLINE,
style,
"using `print!()` with a format string that ends in a single newline"
}
declare_clippy_lint! {
/// **What it does:** Checks for printing on *stdout*. The purpose of this lint
/// is to catch debugging remnants.
///
/// **Why is this bad?** People often print on *stdout* while debugging an
/// application and might forget to remove those prints afterward.
///
/// **Known problems:** Only catches `print!` and `println!` calls.
///
/// **Example:**
/// ```rust
/// println!("Hello world!");
/// ```
pub PRINT_STDOUT,
restriction,
"printing on stdout"
}
declare_clippy_lint! {
/// **What it does:** Checks for printing on *stderr*. The purpose of this lint
/// is to catch debugging remnants.
///
/// **Why is this bad?** People often print on *stderr* while debugging an
/// application and might forget to remove those prints afterward.
///
/// **Known problems:** Only catches `eprint!` and `eprintln!` calls.
///
/// **Example:**
/// ```rust
/// eprintln!("Hello world!");
/// ```
pub PRINT_STDERR,
restriction,
"printing on stderr"
}
declare_clippy_lint! {
/// **What it does:** Checks for use of `Debug` formatting. The purpose of this
/// lint is to catch debugging remnants.
///
/// **Why is this bad?** The purpose of the `Debug` trait is to facilitate
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/// debugging Rust code. It should not be used in user-facing output.
///
/// **Example:**
/// ```rust
/// # let foo = "bar";
/// println!("{:?}", foo);
/// ```
pub USE_DEBUG,
restriction,
"use of `Debug`-based formatting"
}
declare_clippy_lint! {
/// **What it does:** This lint warns about the use of literals as `print!`/`println!` args.
///
/// **Why is this bad?** Using literals as `println!` args is inefficient
/// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
/// (i.e., just put the literal in the format string)
///
/// **Known problems:** Will also warn with macro calls as arguments that expand to literals
/// -- e.g., `println!("{}", env!("FOO"))`.
///
/// **Example:**
/// ```rust
/// println!("{}", "foo");
/// ```
/// use the literal without formatting:
/// ```rust
/// println!("foo");
/// ```
pub PRINT_LITERAL,
style,
"printing a literal with a format string"
}
declare_clippy_lint! {
/// **What it does:** This lint warns when you use `writeln!(buf, "")` to
/// print a newline.
///
/// **Why is this bad?** You should use `writeln!(buf)`, which is simpler.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # use std::fmt::Write;
/// # let mut buf = String::new();
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/// // Bad
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/// writeln!(buf, "");
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///
/// // Good
/// writeln!(buf);
/// ```
pub WRITELN_EMPTY_STRING,
style,
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"using `writeln!(buf, \"\")` with an empty string"
}
declare_clippy_lint! {
/// **What it does:** This lint warns when you use `write!()` with a format
/// string that
/// ends in a newline.
///
/// **Why is this bad?** You should use `writeln!()` instead, which appends the
/// newline.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # use std::fmt::Write;
/// # let mut buf = String::new();
/// # let name = "World";
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/// // Bad
/// write!(buf, "Hello {}!\n", name);
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///
/// // Good
/// writeln!(buf, "Hello {}!", name);
/// ```
pub WRITE_WITH_NEWLINE,
style,
"using `write!()` with a format string that ends in a single newline"
}
declare_clippy_lint! {
/// **What it does:** This lint warns about the use of literals as `write!`/`writeln!` args.
///
/// **Why is this bad?** Using literals as `writeln!` args is inefficient
/// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
/// (i.e., just put the literal in the format string)
///
/// **Known problems:** Will also warn with macro calls as arguments that expand to literals
/// -- e.g., `writeln!(buf, "{}", env!("FOO"))`.
///
/// **Example:**
/// ```rust
/// # use std::fmt::Write;
/// # let mut buf = String::new();
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/// // Bad
/// writeln!(buf, "{}", "foo");
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///
/// // Good
/// writeln!(buf, "foo");
/// ```
pub WRITE_LITERAL,
style,
"writing a literal with a format string"
}
#[derive(Default)]
pub struct Write {
in_debug_impl: bool,
}
impl_lint_pass!(Write => [
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PRINT_WITH_NEWLINE,
PRINTLN_EMPTY_STRING,
PRINT_STDOUT,
PRINT_STDERR,
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USE_DEBUG,
PRINT_LITERAL,
WRITE_WITH_NEWLINE,
WRITELN_EMPTY_STRING,
WRITE_LITERAL
]);
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impl EarlyLintPass for Write {
fn check_item(&mut self, _: &EarlyContext<'_>, item: &Item) {
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if let ItemKind::Impl(box ImplKind {
of_trait: Some(trait_ref),
..
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}) = &item.kind
{
let trait_name = trait_ref
.path
.segments
.iter()
.last()
.expect("path has at least one segment")
.ident
.name;
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if trait_name == sym::Debug {
self.in_debug_impl = true;
}
}
}
fn check_item_post(&mut self, _: &EarlyContext<'_>, _: &Item) {
self.in_debug_impl = false;
}
fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &MacCall) {
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fn is_build_script(cx: &EarlyContext<'_>) -> bool {
// Cargo sets the crate name for build scripts to `build_script_build`
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cx.sess
.opts
.crate_name
.as_ref()
.map_or(false, |crate_name| crate_name == "build_script_build")
}
if mac.path == sym!(print) {
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if !is_build_script(cx) {
span_lint(cx, PRINT_STDOUT, mac.span(), "use of `print!`");
}
self.lint_print_with_newline(cx, mac);
} else if mac.path == sym!(println) {
if !is_build_script(cx) {
span_lint(cx, PRINT_STDOUT, mac.span(), "use of `println!`");
}
self.lint_println_empty_string(cx, mac);
} else if mac.path == sym!(eprint) {
span_lint(cx, PRINT_STDERR, mac.span(), "use of `eprint!`");
self.lint_print_with_newline(cx, mac);
} else if mac.path == sym!(eprintln) {
span_lint(cx, PRINT_STDERR, mac.span(), "use of `eprintln!`");
self.lint_println_empty_string(cx, mac);
} else if mac.path == sym!(write) {
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if let (Some(fmt_str), _) = self.check_tts(cx, mac.args.inner_tokens(), true) {
if check_newlines(&fmt_str) {
span_lint_and_then(
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cx,
WRITE_WITH_NEWLINE,
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mac.span(),
"using `write!()` with a format string that ends in a single newline",
|err| {
err.multipart_suggestion(
"use `writeln!()` instead",
vec![
(mac.path.span, String::from("writeln")),
(newline_span(&fmt_str), String::new()),
],
Applicability::MachineApplicable,
);
},
)
}
}
} else if mac.path == sym!(writeln) {
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if let (Some(fmt_str), expr) = self.check_tts(cx, mac.args.inner_tokens(), true) {
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if fmt_str.symbol == kw::Empty {
let mut applicability = Applicability::MachineApplicable;
// FIXME: remove this `#[allow(...)]` once the issue #5822 gets fixed
#[allow(clippy::option_if_let_else)]
let suggestion = if let Some(e) = expr {
snippet_with_applicability(cx, e.span, "v", &mut applicability)
} else {
applicability = Applicability::HasPlaceholders;
Cow::Borrowed("v")
};
span_lint_and_sugg(
cx,
WRITELN_EMPTY_STRING,
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mac.span(),
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format!("using `writeln!({}, \"\")`", suggestion).as_str(),
"replace it with",
format!("writeln!({})", suggestion),
applicability,
);
}
}
}
}
}
/// Given a format string that ends in a newline and its span, calculates the span of the
/// newline, or the format string itself if the format string consists solely of a newline.
fn newline_span(fmtstr: &StrLit) -> Span {
let sp = fmtstr.span;
let contents = &fmtstr.symbol.as_str();
if *contents == r"\n" {
return sp;
}
let newline_sp_hi = sp.hi()
- match fmtstr.style {
StrStyle::Cooked => BytePos(1),
StrStyle::Raw(hashes) => BytePos((1 + hashes).into()),
};
let newline_sp_len = if contents.ends_with('\n') {
BytePos(1)
} else if contents.ends_with(r"\n") {
BytePos(2)
} else {
panic!("expected format string to contain a newline");
};
sp.with_lo(newline_sp_hi - newline_sp_len).with_hi(newline_sp_hi)
}
impl Write {
/// Checks the arguments of `print[ln]!` and `write[ln]!` calls. It will return a tuple of two
/// `Option`s. The first `Option` of the tuple is the macro's format string. It includes
/// the contents of the string, whether it's a raw string, and the span of the literal in the
/// source. The second `Option` in the tuple is, in the `write[ln]!` case, the expression the
/// `format_str` should be written to.
///
/// Example:
///
/// Calling this function on
/// ```rust
/// # use std::fmt::Write;
/// # let mut buf = String::new();
/// # let something = "something";
/// writeln!(buf, "string to write: {}", something);
/// ```
/// will return
/// ```rust,ignore
/// (Some("string to write: {}"), Some(buf))
/// ```
#[allow(clippy::too_many_lines)]
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fn check_tts<'a>(&self, cx: &EarlyContext<'a>, tts: TokenStream, is_write: bool) -> (Option<StrLit>, Option<Expr>) {
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use rustc_parse_format::{
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AlignUnknown, ArgumentImplicitlyIs, ArgumentIs, ArgumentNamed, CountImplied, FormatSpec, ParseMode, Parser,
Piece,
};
let mut parser = parser::Parser::new(&cx.sess.parse_sess, tts, false, None);
let mut expr: Option<Expr> = None;
if is_write {
expr = match parser.parse_expr().map_err(|mut err| err.cancel()) {
Ok(p) => Some(p.into_inner()),
Err(_) => return (None, None),
};
// might be `writeln!(foo)`
if parser.expect(&token::Comma).map_err(|mut err| err.cancel()).is_err() {
return (None, expr);
}
}
let fmtstr = match parser.parse_str_lit() {
Ok(fmtstr) => fmtstr,
Err(_) => return (None, expr),
};
let tmp = fmtstr.symbol.as_str();
let mut args = vec![];
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let mut fmt_parser = Parser::new(&tmp, None, None, false, ParseMode::Format);
while let Some(piece) = fmt_parser.next() {
if !fmt_parser.errors.is_empty() {
return (None, expr);
}
if let Piece::NextArgument(arg) = piece {
if !self.in_debug_impl && arg.format.ty == "?" {
// FIXME: modify rustc's fmt string parser to give us the current span
span_lint(cx, USE_DEBUG, parser.prev_token.span, "use of `Debug`-based formatting");
}
args.push(arg);
}
}
let lint = if is_write { WRITE_LITERAL } else { PRINT_LITERAL };
let mut idx = 0;
loop {
const SIMPLE: FormatSpec<'_> = FormatSpec {
fill: None,
align: AlignUnknown,
flags: 0,
precision: CountImplied,
precision_span: None,
width: CountImplied,
width_span: None,
ty: "",
ty_span: None,
};
if !parser.eat(&token::Comma) {
return (Some(fmtstr), expr);
}
let token_expr = if let Ok(expr) = parser.parse_expr().map_err(|mut err| err.cancel()) {
expr
} else {
return (Some(fmtstr), None);
};
match &token_expr.kind {
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ExprKind::Lit(lit) if !matches!(lit.kind, LitKind::Int(..) | LitKind::Float(..)) => {
let mut all_simple = true;
let mut seen = false;
for arg in &args {
match arg.position {
ArgumentImplicitlyIs(n) | ArgumentIs(n) => {
if n == idx {
all_simple &= arg.format == SIMPLE;
seen = true;
}
},
ArgumentNamed(_) => {},
}
}
if all_simple && seen {
span_lint(cx, lint, token_expr.span, "literal with an empty format string");
}
idx += 1;
},
ExprKind::Assign(lhs, rhs, _) => {
if_chain! {
if let ExprKind::Lit(ref lit) = rhs.kind;
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if !matches!(lit.kind, LitKind::Int(..) | LitKind::Float(..));
if let ExprKind::Path(_, p) = &lhs.kind;
then {
let mut all_simple = true;
let mut seen = false;
for arg in &args {
match arg.position {
ArgumentImplicitlyIs(_) | ArgumentIs(_) => {},
ArgumentNamed(name) => {
if *p == name {
seen = true;
all_simple &= arg.format == SIMPLE;
}
},
}
}
if all_simple && seen {
span_lint(cx, lint, rhs.span, "literal with an empty format string");
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}
}
}
},
_ => idx += 1,
}
}
}
fn lint_println_empty_string(&self, cx: &EarlyContext<'_>, mac: &MacCall) {
if let (Some(fmt_str), _) = self.check_tts(cx, mac.args.inner_tokens(), false) {
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if fmt_str.symbol == kw::Empty {
let name = mac.path.segments[0].ident.name;
span_lint_and_sugg(
cx,
PRINTLN_EMPTY_STRING,
mac.span(),
&format!("using `{}!(\"\")`", name),
"replace it with",
format!("{}!()", name),
Applicability::MachineApplicable,
);
}
}
}
fn lint_print_with_newline(&self, cx: &EarlyContext<'_>, mac: &MacCall) {
if let (Some(fmt_str), _) = self.check_tts(cx, mac.args.inner_tokens(), false) {
if check_newlines(&fmt_str) {
let name = mac.path.segments[0].ident.name;
let suggested = format!("{}ln", name);
span_lint_and_then(
cx,
PRINT_WITH_NEWLINE,
mac.span(),
&format!("using `{}!()` with a format string that ends in a single newline", name),
|err| {
err.multipart_suggestion(
&format!("use `{}!` instead", suggested),
vec![(mac.path.span, suggested), (newline_span(&fmt_str), String::new())],
Applicability::MachineApplicable,
);
},
);
}
}
}
}
/// Checks if the format string contains a single newline that terminates it.
///
/// Literal and escaped newlines are both checked (only literal for raw strings).
fn check_newlines(fmtstr: &StrLit) -> bool {
let mut has_internal_newline = false;
let mut last_was_cr = false;
let mut should_lint = false;
let contents = &fmtstr.symbol.as_str();
let mut cb = |r: Range<usize>, c: Result<char, EscapeError>| {
let c = c.unwrap();
if r.end == contents.len() && c == '\n' && !last_was_cr && !has_internal_newline {
should_lint = true;
} else {
last_was_cr = c == '\r';
if c == '\n' {
has_internal_newline = true;
}
}
};
match fmtstr.style {
StrStyle::Cooked => unescape::unescape_literal(contents, unescape::Mode::Str, &mut cb),
StrStyle::Raw(_) => unescape::unescape_literal(contents, unescape::Mode::RawStr, &mut cb),
}
should_lint
}