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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::macros::FormatArgsExpn;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::{is_expn_of, match_function_call, paths};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::def::Res;
use rustc_hir::{BindingAnnotation, Block, BlockCheckMode, Expr, ExprKind, Node, PatKind, QPath, Stmt, StmtKind};
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";
/// writeln!(&mut std::io::stderr(), "foo: {:?}", bar).unwrap();
/// writeln!(&mut std::io::stdout(), "foo: {:?}", bar).unwrap();
/// ```
///
/// Use instead:
/// ```rust
/// # use std::io::Write;
/// # let bar = "furchtbar";
/// eprintln!("foo: {:?}", bar);
/// println!("foo: {:?}", bar);
/// ```
#[clippy::version = "pre 1.29.0"]
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], _) = look_in_block(cx, &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(cx, 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 mut applicability = Applicability::MachineApplicable;
let inputs_snippet = snippet_with_applicability(
cx,
format_args.inputs_span(),
"..",
&mut applicability,
);
span_lint_and_sugg(
cx,
EXPLICIT_WRITE,
expr.span,
&format!("use of `{}.unwrap()`", used),
"try this",
format!("{}{}!({})", prefix, sugg_mac, inputs_snippet),
applicability,
)
}
}
}
}
/// If `kind` is a block that looks like `{ let result = $expr; result }` then
/// returns $expr. Otherwise returns `kind`.
fn look_in_block<'tcx, 'hir>(cx: &LateContext<'tcx>, kind: &'tcx ExprKind<'hir>) -> &'tcx ExprKind<'hir> {
if_chain! {
if let ExprKind::Block(block, _label @ None) = kind;
if let Block {
stmts: [Stmt { kind: StmtKind::Local(local), .. }],
expr: Some(expr_end_of_block),
rules: BlockCheckMode::DefaultBlock,
..
} = block;
// Find id of the local that expr_end_of_block resolves to
if let ExprKind::Path(QPath::Resolved(None, expr_path)) = expr_end_of_block.kind;
if let Res::Local(expr_res) = expr_path.res;
if let Some(Node::Pat(res_pat)) = cx.tcx.hir().find(expr_res);
// Find id of the local we found in the block
if let PatKind::Binding(BindingAnnotation::Unannotated, local_hir_id, _ident, None) = local.pat.kind;
// If those two are the same hir id
if res_pat.hir_id == local_hir_id;
if let Some(init) = local.init;
then {
return &init.kind;
}
}
kind
}
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