Add allow-mixed-uninlined-format-args config

Implement `allow-mixed-uninlined-format-args` config param to change the behavior of the `uninlined_format_args` lint. Now it is a part of `style`, and won't propose inlining in case of a mixed usage, e.g. `print!("{} {}", var, 1+2)`. If the user sets allow-mixed-uninlined-format-args config param to `false`, then it would behave like before, proposing to inline args even in the mixed case.

Author: nyurik

clippy_lints/src/format_args.rs

@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
 use clippy_utils::is_diag_trait_item;
-use clippy_utils::macros::FormatParamKind::{Implicit, Named, Numbered, Starred};
+use clippy_utils::macros::FormatParamKind::{Implicit, Named, NamedInline, Numbered, Starred};
 use clippy_utils::macros::{
     is_format_macro, is_panic, root_macro_call, Count, FormatArg, FormatArgsExpn, FormatParam, FormatParamUsage,
 };
@@ -106,19 +106,25 @@ declare_clippy_lint! {
     /// format!("{var:.prec$}");
     /// ```
     ///
-    /// ### Known Problems
-    ///
-    /// There may be a false positive if the format string is expanded from certain proc macros:
-    ///
-    /// ```ignore
-    /// println!(indoc!("{}"), var);
+    /// If allow-mixed-uninlined-format-args is set to false in clippy.toml,
+    /// the following code will also trigger the lint:
+    /// ```rust
+    /// # let var = 42;
+    /// format!("{} {}", var, 1+2);
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// # let var = 42;
+    /// format!("{var} {}", 1+2);
     /// ```
     ///
+    /// ### Known Problems
+    ///
     /// If a format string contains a numbered argument that cannot be inlined
     /// nothing will be suggested, e.g. `println!("{0}={1}", var, 1+2)`.
     #[clippy::version = "1.65.0"]
     pub UNINLINED_FORMAT_ARGS,
-    pedantic,
+    style,
     "using non-inlined variables in `format!` calls"
 }
 
@@ -162,12 +168,16 @@ impl_lint_pass!(FormatArgs => [
 
 pub struct FormatArgs {
     msrv: Msrv,
+    ignore_mixed: bool,
 }
 
 impl FormatArgs {
     #[must_use]
-    pub fn new(msrv: Msrv) -> Self {
-        Self { msrv }
+    pub fn new(msrv: Msrv, allow_mixed_uninlined_format_args: bool) -> Self {
+        Self {
+            msrv,
+            ignore_mixed: allow_mixed_uninlined_format_args,
+        }
     }
 }
 
@@ -192,7 +202,7 @@ impl<'tcx> LateLintPass<'tcx> for FormatArgs {
                 check_to_string_in_format_args(cx, name, arg.param.value);
             }
             if self.msrv.meets(msrvs::FORMAT_ARGS_CAPTURE) {
-                check_uninlined_args(cx, &format_args, outermost_expn_data.call_site, macro_def_id);
+                check_uninlined_args(cx, &format_args, outermost_expn_data.call_site, macro_def_id, self.ignore_mixed);
             }
         }
     }
@@ -270,7 +280,13 @@ fn check_unused_format_specifier(cx: &LateContext<'_>, arg: &FormatArg<'_>) {
     }
 }
 
-fn check_uninlined_args(cx: &LateContext<'_>, args: &FormatArgsExpn<'_>, call_site: Span, def_id: DefId) {
+fn check_uninlined_args(
+    cx: &LateContext<'_>,
+    args: &FormatArgsExpn<'_>,
+    call_site: Span,
+    def_id: DefId,
+    ignore_mixed: bool,
+) {
     if args.format_string.span.from_expansion() {
         return;
     }
@@ -285,7 +301,7 @@ fn check_uninlined_args(cx: &LateContext<'_>, args: &FormatArgsExpn<'_>, call_si
     // we cannot remove any other arguments in the format string,
     // because the index numbers might be wrong after inlining.
     // Example of an un-inlinable format:  print!("{}{1}", foo, 2)
-    if !args.params().all(|p| check_one_arg(args, &p, &mut fixes)) || fixes.is_empty() {
+    if !args.params().all(|p| check_one_arg(args, &p, &mut fixes, ignore_mixed)) || fixes.is_empty() {
         return;
     }
 
@@ -305,11 +321,23 @@ fn check_uninlined_args(cx: &LateContext<'_>, args: &FormatArgsExpn<'_>, call_si
                 Applicability::MachineApplicable,
                 if multiline_fix { CompletelyHidden } else { ShowCode },
             );
+            if ignore_mixed {
+                // Improve lint config discoverability
+                diag.note_once(
+                    "this lint can also fix mixed format arg inlining if \
+                    `allow-mixed-uninlined-format-args = false` is set in the `clippy.toml` file",
+                );
+            }
         },
     );
 }
 
-fn check_one_arg(args: &FormatArgsExpn<'_>, param: &FormatParam<'_>, fixes: &mut Vec<(Span, String)>) -> bool {
+fn check_one_arg(
+    args: &FormatArgsExpn<'_>,
+    param: &FormatParam<'_>,
+    fixes: &mut Vec<(Span, String)>,
+    ignore_mixed: bool,
+) -> bool {
     if matches!(param.kind, Implicit | Starred | Named(_) | Numbered)
         && let ExprKind::Path(QPath::Resolved(None, path)) = param.value.kind
         && let [segment] = path.segments
@@ -324,8 +352,10 @@ fn check_one_arg(args: &FormatArgsExpn<'_>, param: &FormatParam<'_>, fixes: &mut
         fixes.push((arg_span, String::new()));
         true  // successful inlining, continue checking
     } else {
-        // if we can't inline a numbered argument, we can't continue
-        param.kind != Numbered
+        // Do not continue inlining (return false) in case
+        // * if we can't inline a numbered argument, e.g. `print!("{0} ...", foo.bar, ...)`
+        // * if allow_mixed_uninlined_format_args is false and this arg hasn't been inlined already
+        param.kind != Numbered && (!ignore_mixed || matches!(param.kind, NamedInline(_)))
     }
 }
 

clippy_lints/src/lib.rs

@@ -828,7 +828,8 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         ))
     });
     store.register_late_pass(move |_| Box::new(undocumented_unsafe_blocks::UndocumentedUnsafeBlocks));
-    store.register_late_pass(move |_| Box::new(format_args::FormatArgs::new(msrv())));
+    let allow_mixed_uninlined = conf.allow_mixed_uninlined_format_args;
+    store.register_late_pass(move |_| Box::new(format_args::FormatArgs::new(msrv(), allow_mixed_uninlined)));
     store.register_late_pass(|_| Box::new(trailing_empty_array::TrailingEmptyArray));
     store.register_early_pass(|| Box::new(octal_escapes::OctalEscapes));
     store.register_late_pass(|_| Box::new(needless_late_init::NeedlessLateInit));

clippy_lints/src/utils/conf.rs

@@ -402,6 +402,10 @@ define_Conf! {
     /// A list of paths to types that should be treated like `Arc`, i.e. ignored but
     /// for the generic parameters for determining interior mutability
     (ignore_interior_mutability: Vec<String> = Vec::from(["bytes::Bytes".into()])),
+    /// Lint: UNINLINED_FORMAT_ARGS.
+    ///
+    /// Whether to allow mixed uninlined format args, e.g. `format!("{} {}", a, foo.bar)`
+    (allow_mixed_uninlined_format_args: bool = true),
 }
 
 /// Search for the configuration file.

tests/ui-toml/allow_mixed_uninlined_format_args/auxiliary/proc_macro_with_span.rs

@@ -0,0 +1,32 @@
+// compile-flags: --emit=link
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+
+use proc_macro::{token_stream::IntoIter, Group, Span, TokenStream, TokenTree};
+
+#[proc_macro]
+pub fn with_span(input: TokenStream) -> TokenStream {
+    let mut iter = input.into_iter();
+    let span = iter.next().unwrap().span();
+    let mut res = TokenStream::new();
+    write_with_span(span, iter, &mut res);
+    res
+}
+
+fn write_with_span(s: Span, input: IntoIter, out: &mut TokenStream) {
+    for mut tt in input {
+        if let TokenTree::Group(g) = tt {
+            let mut stream = TokenStream::new();
+            write_with_span(s, g.stream().into_iter(), &mut stream);
+            let mut group = Group::new(g.delimiter(), stream);
+            group.set_span(s);
+            out.extend([TokenTree::Group(group)]);
+        } else {
+            tt.set_span(s);
+            out.extend([tt]);
+        }
+    }
+}

tests/ui-toml/allow_mixed_uninlined_format_args/clippy.toml

@@ -0,0 +1 @@
+allow-mixed-uninlined-format-args = false

tests/ui-toml/allow_mixed_uninlined_format_args/uninlined_format_args.fixed

@@ -0,0 +1,177 @@
+// aux-build:proc_macro_with_span.rs
+// run-rustfix
+#![feature(custom_inner_attributes)]
+#![warn(clippy::uninlined_format_args)]
+#![allow(named_arguments_used_positionally, unused_imports, unused_macros, unused_variables)]
+#![allow(clippy::eq_op, clippy::format_in_format_args, clippy::print_literal)]
+
+extern crate proc_macro_with_span;
+use proc_macro_with_span::with_span;
+
+macro_rules! no_param_str {
+    () => {
+        "{}"
+    };
+}
+
+macro_rules! my_println {
+   ($($args:tt),*) => {{
+        println!($($args),*)
+    }};
+}
+
+macro_rules! my_println_args {
+    ($($args:tt),*) => {{
+        println!("foo: {}", format_args!($($args),*))
+    }};
+}
+
+fn tester(fn_arg: i32) {
+    let local_i32 = 1;
+    let local_f64 = 2.0;
+    let local_opt: Option<i32> = Some(3);
+    let width = 4;
+    let prec = 5;
+    let val = 6;
+
+    // make sure this file hasn't been corrupted with tabs converted to spaces
+    // let _ = '	';  // <- this is a single tab character
+    let _: &[u8; 3] = b"	 	"; // <- <tab><space><tab>
+
+    println!("val='{local_i32}'");
+    println!("val='{local_i32}'"); // 3 spaces
+    println!("val='{local_i32}'"); // tab
+    println!("val='{local_i32}'"); // space+tab
+    println!("val='{local_i32}'"); // tab+space
+    println!(
+        "val='{local_i32}'"
+    );
+    println!("{local_i32}");
+    println!("{fn_arg}");
+    println!("{local_i32:?}");
+    println!("{local_i32:#?}");
+    println!("{local_i32:4}");
+    println!("{local_i32:04}");
+    println!("{local_i32:<3}");
+    println!("{local_i32:#010x}");
+    println!("{local_f64:.1}");
+    println!("Hello {} is {local_f64:.local_i32$}", "x");
+    println!("Hello {local_i32} is {local_f64:.*}", 5);
+    println!("Hello {local_i32} is {local_f64:.*}", 5);
+    println!("{local_i32} {local_f64}");
+    println!("{local_i32}, {}", local_opt.unwrap());
+    println!("{val}");
+    println!("{val}");
+    println!("{} {1}", local_i32, 42);
+    println!("val='{local_i32}'");
+    println!("val='{local_i32}'");
+    println!("val='{local_i32}'");
+    println!("val='{fn_arg}'");
+    println!("{local_i32}");
+    println!("{local_i32:?}");
+    println!("{local_i32:#?}");
+    println!("{local_i32:04}");
+    println!("{local_i32:<3}");
+    println!("{local_i32:#010x}");
+    println!("{local_f64:.1}");
+    println!("{local_i32} {local_i32}");
+    println!("{local_f64} {local_i32} {local_i32} {local_f64}");
+    println!("{local_i32} {local_f64}");
+    println!("{local_f64} {local_i32}");
+    println!("{local_f64} {local_i32} {local_f64} {local_i32}");
+    println!("{1} {0}", "str", local_i32);
+    println!("{local_i32}");
+    println!("{local_i32:width$}");
+    println!("{local_i32:width$}");
+    println!("{local_i32:.prec$}");
+    println!("{local_i32:.prec$}");
+    println!("{val:val$}");
+    println!("{val:val$}");
+    println!("{val:val$.val$}");
+    println!("{val:val$.val$}");
+    println!("{val:val$.val$}");
+    println!("{val:val$.val$}");
+    println!("{val:val$.val$}");
+    println!("{val:val$.val$}");
+    println!("{val:val$.val$}");
+    println!("{val:val$.val$}");
+    println!("{width:width$}");
+    println!("{local_i32:width$}");
+    println!("{width:width$}");
+    println!("{local_i32:width$}");
+    println!("{prec:.prec$}");
+    println!("{local_i32:.prec$}");
+    println!("{prec:.prec$}");
+    println!("{local_i32:.prec$}");
+    println!("{width:width$.prec$}");
+    println!("{width:width$.prec$}");
+    println!("{local_f64:width$.prec$}");
+    println!("{local_f64:width$.prec$} {local_f64} {width} {prec}");
+    println!(
+        "{local_i32:width$.prec$} {local_i32:prec$.width$} {width:local_i32$.prec$} {width:prec$.local_i32$} {prec:local_i32$.width$} {prec:width$.local_i32$}",
+    );
+    println!(
+        "{0:1$.2$} {0:2$.1$} {1:0$.2$} {1:2$.0$} {2:0$.1$} {2:1$.0$} {3}",
+        local_i32,
+        width,
+        prec,
+        1 + 2
+    );
+    println!("Width = {local_i32}, value with width = {local_f64:local_i32$}");
+    println!("{local_i32:width$.prec$}");
+    println!("{width:width$.prec$}");
+    println!("{}", format!("{local_i32}"));
+    my_println!("{}", local_i32);
+    my_println_args!("{}", local_i32);
+
+    // these should NOT be modified by the lint
+    println!(concat!("nope ", "{}"), local_i32);
+    println!("val='{local_i32}'");
+    println!("val='{local_i32 }'");
+    println!("val='{local_i32	}'"); // with tab
+    println!("val='{local_i32\n}'");
+    println!("{}", usize::MAX);
+    println!("{}", local_opt.unwrap());
+    println!(
+        "val='{local_i32
+    }'"
+    );
+    println!(no_param_str!(), local_i32);
+
+    println!(
+        "{val}",
+    );
+    println!("{val}");
+
+    println!(with_span!("{0} {1}" "{1} {0}"), local_i32, local_f64);
+    println!("{}", with_span!(span val));
+
+    if local_i32 > 0 {
+        panic!("p1 {local_i32}");
+    }
+    if local_i32 > 0 {
+        panic!("p2 {local_i32}");
+    }
+    if local_i32 > 0 {
+        panic!("p3 {local_i32}");
+    }
+    if local_i32 > 0 {
+        panic!("p4 {local_i32}");
+    }
+}
+
+fn main() {
+    tester(42);
+}
+
+fn _under_msrv() {
+    #![clippy::msrv = "1.57"]
+    let local_i32 = 1;
+    println!("don't expand='{}'", local_i32);
+}
+
+fn _meets_msrv() {
+    #![clippy::msrv = "1.58"]
+    let local_i32 = 1;
+    println!("expand='{local_i32}'");
+}