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use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
use clippy_utils::higher::FormatArgsExpn;
use clippy_utils::{is_expn_of, match_function_call, paths};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for usage of `write!()` / `writeln()!` which can be
/// replaced with `(e)print!()` / `(e)println!()`
///
/// ### Why is this bad?
/// Using `(e)println! is clearer and more concise
///
/// ### Example
/// ```rust
/// # use std::io::Write;
/// # let bar = "furchtbar";
/// // this would be clearer as `eprintln!("foo: {:?}", bar);`
/// writeln!(&mut std::io::stderr(), "foo: {:?}", bar).unwrap();
/// ```
pub EXPLICIT_WRITE,
complexity,
"using the `write!()` family of functions instead of the `print!()` family of functions, when using the latter would work"
}
declare_lint_pass!(ExplicitWrite => [EXPLICIT_WRITE]);
impl<'tcx> LateLintPass<'tcx> for ExplicitWrite {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if_chain! {
// match call to unwrap
if let ExprKind::MethodCall(unwrap_fun, _, [write_call], _) = expr.kind;
if unwrap_fun.ident.name == sym::unwrap;
// match call to write_fmt
if let ExprKind::MethodCall(write_fun, _, [write_recv, write_arg], _) = write_call.kind;
if write_fun.ident.name == sym!(write_fmt);
// match calls to std::io::stdout() / std::io::stderr ()
if let Some(dest_name) = if match_function_call(cx, write_recv, &paths::STDOUT).is_some() {
Some("stdout")
} else if match_function_call(cx, write_recv, &paths::STDERR).is_some() {
Some("stderr")
} else {
None
};
if let Some(format_args) = FormatArgsExpn::parse(write_arg);
then {
let calling_macro =
// ordering is important here, since `writeln!` uses `write!` internally
if is_expn_of(write_call.span, "writeln").is_some() {
Some("writeln")
} else if is_expn_of(write_call.span, "write").is_some() {
Some("write")
} else {
None
};
let prefix = if dest_name == "stderr" {
"e"
} else {
""
};
// We need to remove the last trailing newline from the string because the
// underlying `fmt::write` function doesn't know whether `println!` or `print!` was
// used.
let (used, sugg_mac) = if let Some(macro_name) = calling_macro {
(
format!("{}!({}(), ...)", macro_name, dest_name),
macro_name.replace("write", "print"),
)
} else {
(
format!("{}().write_fmt(...)", dest_name),
"print".into(),
)
};
let msg = format!("use of `{}.unwrap()`", used);
if let [write_output] = *format_args.format_string_symbols {
let mut write_output = write_output.to_string();
if write_output.ends_with('\n') {
write_output.pop();
}
let sugg = format!("{}{}!(\"{}\")", prefix, sugg_mac, write_output.escape_default());
span_lint_and_sugg(
cx,
EXPLICIT_WRITE,
expr.span,
&msg,
"try this",
sugg,
Applicability::MachineApplicable
);
} else {
// We don't have a proper suggestion
let help = format!("consider using `{}{}!` instead", prefix, sugg_mac);
span_lint_and_help(cx, EXPLICIT_WRITE, expr.span, &msg, None, &help);
}
}
}
}
}
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