Migrate format_args.rs to rustc_ast::FormatArgs

[Alexendoo]

changelog: none

Part of #10233

Empty precision specifiers are no longer linted as the span for that isn't present in FormatOptions

format!("{:.}", ...)

That could be fixed later with some hackery or a change upstream

r? @flip1995

[Alexendoo]

This is a slightly simplified version of

rust-clippy/clippy_utils/src/macros.rs

Lines 932 to 992 in f19db28

	/// Gets the spans of the commas inbetween the format string and explicit args, not including
	/// any trailing comma
	///
	/// ```ignore
	/// format!("{} {}", a, b)
	/// // ^ ^
	/// ```
	///
	/// Ensures that the format string and values aren't coming from a proc macro that sets the
	/// output span to that of its input
	fn comma_spans(cx: &LateContext<'_>, explicit_values: &[&Expr<'_>], fmt_span: Span) -> Option<Vec<Span>> {
	// `format!("{} {} {c}", "one", "two", c = "three")`
	// ^^^^^ ^^^^^ ^^^^^^^
	let value_spans = explicit_values
	.iter()
	.map(|val| hygiene::walk_chain(val.span, fmt_span.ctxt()));
	// `format!("{} {} {c}", "one", "two", c = "three")`
	// ^^ ^^ ^^^^^^
	let between_spans = once(fmt_span)
	.chain(value_spans)
	.tuple_windows()
	.map(|(start, end)| start.between(end));
	let mut comma_spans = Vec::new();
	for between_span in between_spans {
	let mut offset = 0;
	let mut seen_comma = false;
	for token in tokenize(&snippet_opt(cx, between_span)?) {
	match token.kind {
	TokenKind::LineComment { .. } | TokenKind::BlockComment { .. } | TokenKind::Whitespace => {},
	TokenKind::Comma if !seen_comma => {
	seen_comma = true;
	let base = between_span.data();
	comma_spans.push(Span::new(
	base.lo + BytePos(offset),
	base.lo + BytePos(offset + 1),
	base.ctxt,
	base.parent,
	));
	},
	// named arguments, `start_val, name = end_val`
	// ^^^^^^^^^ between_span
	TokenKind::Ident | TokenKind::Eq if seen_comma => {},
	// An unexpected token usually indicates the format string or a value came from a proc macro output
	// that sets the span of its output to an input, e.g. `println!(some_proc_macro!("input"), ..)` that
	// emits a string literal with the span set to that of `"input"`
	_ => return None,
	}
	offset += token.len;
	}
	if !seen_comma {
	return None;
	}
	}
	Some(comma_spans)
	}

[Alexendoo]

This is a bug with root_macro_call_first_node, not sure why but it doesn't pick up that format!() as a macro call

[Alexendoo]

clippy_utils depends on this already so it's not a new dependency

[m-ou-se]

Empty precision specifiers are no longer linted as the span for that isn't present in FormatOptions

format!("{:.}", ...)

We should probably just move that warning to rustc, since an empty . specifier is always useless.

[nyurik]

I tried to apply a similar change to explicit_write.rs , and root_macro_call_first_node wasn't a drop-in replacement for FormatArgsExpn::parse. Most likely i am doing something totally wrong. Something like this partially works, but is probably wrong as well:

if let ExprKind::MethodCall(unwrap_fun, write_call, [], _) = expr.kind
    && unwrap_fun.ident.name == sym::unwrap
    // match call to write_fmt
    && let ExprKind::MethodCall(write_fun, write_recv, [write_arg], _) = look_in_block(cx, &write_call.kind)
    && let ExprKind::Call(_, write_arg2) = look_in_block(cx, &write_arg.kind)
    && write_fun.ident.name == sym!(write_fmt)
    // match calls to std::io::stdout() / std::io::stderr ()
    && 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
    }
    && let Some(format_args) = root_macro_call_first_node(cx, write_call)
    && is_format_macro(cx, format_args.def_id)
    // && let Some(format_args2) = FormatArgsExpn::find_nested(cx, expr, format_args.expn)

[Alexendoo]

The replacement would be find_format_args. The root_macro_call_first_node would be detecting the write[ln] macro call there, not format_args

You wouldn't need is_format_macro as it's already checking the macro kind below that, but if you're using root_macro_call_first_node it could replace the two is_expn_of checks with a match cx.tcx.get_diagnostic_name(macro_call.def_id) { .. }

[Manishearth]

praise: this is neat

[Manishearth]

@bors r+

[bors]

📌 Commit 3259b48 has been approved by Manishearth

It is now in the queue for this repository.

[bors]

⌛ Testing commit 3259b48 with merge 84e42fb...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Manishearth
Pushing 84e42fb to master...