Lint nested format_args! for uninlined args

Previously a `format_args!` call or a macro marked `clippy::format_args`
would not be linted for uninlined arguments when one of the arguments
was in turn a `format_args!` call.

Author: Linus Kirkwood

clippy_lints/src/format_args.rs

@@ -295,7 +295,7 @@ impl<'tcx> LateLintPass<'tcx> for FormatArgs<'tcx> {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
         if let Some(macro_call) = root_macro_call_first_node(cx, expr)
             && is_format_macro(cx, macro_call.def_id)
-            && let Some(format_args) = self.format_args.get(cx, expr, macro_call.expn)
+            && let Some(mut format_args) = self.format_args.get(cx, expr, macro_call.expn)
         {
             let mut linter = FormatArgsExpr {
                 cx,
@@ -312,8 +312,34 @@ impl<'tcx> LateLintPass<'tcx> for FormatArgs<'tcx> {
             linter.check_trailing_comma();
             linter.check_templates();
 
-            if self.msrv.meets(cx, msrvs::FORMAT_ARGS_CAPTURE) {
-                linter.check_uninlined_args();
+            if !self.msrv.meets(cx, msrvs::FORMAT_ARGS_CAPTURE) {
+                return;
+            }
+
+            let mut uninlined_queue = vec![];
+            loop {
+                if linter.check_uninlined_args() {
+                    break;
+                }
+
+                uninlined_queue.extend(self.format_args.get_nested(format_args));
+                if let Some(inner_format_args) = uninlined_queue.pop() {
+                    format_args = inner_format_args;
+
+                    linter = FormatArgsExpr {
+                        cx,
+                        expr,
+                        macro_call: &macro_call,
+                        format_args,
+                        ignore_mixed: self.ignore_mixed,
+                        msrv: &self.msrv,
+                        ty_msrv_map: &self.ty_msrv_map,
+                        has_derived_debug: &mut self.has_derived_debug,
+                        has_pointer_format: &mut self.has_pointer_format,
+                    };
+                } else {
+                    break;
+                }
             }
         }
     }
@@ -442,16 +468,16 @@ impl<'tcx> FormatArgsExpr<'_, 'tcx> {
         }
     }
 
-    fn check_uninlined_args(&self) {
+    fn check_uninlined_args(&self) -> bool {
         if self.format_args.span.from_expansion() {
-            return;
+            return false;
         }
         if self.macro_call.span.edition() < Edition2021
             && (is_panic(self.cx, self.macro_call.def_id) || is_assert_macro(self.cx, self.macro_call.def_id))
         {
             // panic!, assert!, and debug_assert! before 2021 edition considers a single string argument as
             // non-format
-            return;
+            return false;
         }
 
         let mut fixes = Vec::new();
@@ -462,12 +488,12 @@ impl<'tcx> FormatArgsExpr<'_, 'tcx> {
         // Example of an un-inlinable format:  print!("{}{1}", foo, 2)
         for (pos, usage) in self.format_arg_positions() {
             if !self.check_one_arg(pos, usage, &mut fixes) {
-                return;
+                return !fixes.is_empty();
             }
         }
 
         if fixes.is_empty() {
-            return;
+            return false;
         }
 
         // multiline span display suggestion is sometimes broken: https://github.com/rust-lang/rust/pull/102729#discussion_r988704308
@@ -494,6 +520,8 @@ impl<'tcx> FormatArgsExpr<'_, 'tcx> {
                 );
             },
         );
+
+        true
     }
 
     fn check_one_arg(&self, pos: &FormatArgPosition, usage: FormatParamUsage, fixes: &mut Vec<(Span, String)>) -> bool {

clippy_utils/src/macros.rs

@@ -433,6 +433,25 @@ impl FormatArgsStorage {
         self.0.get()?.get(&format_args_expr.span.with_parent(None))
     }
 
+    /// Returns AST [`FormatArgs`] nodes if there are any nested inside `parent_format_args`.
+    pub fn get_nested(&self, parent_format_args: &FormatArgs) -> Vec<&FormatArgs> {
+        let mut nested = Vec::new();
+        let format_args_map = match self.0.get() {
+            Some(map) => map,
+            None => return nested,
+        };
+
+        for arg in parent_format_args.arguments.all_args() {
+            if matches!(arg.expr.kind, rustc_ast::ExprKind::FormatArgs(_))
+                && let Some(format_args) = format_args_map.get(&arg.expr.span.with_parent(None))
+            {
+                nested.push(format_args);
+            }
+        }
+
+        nested
+    }
+
     /// Should only be called by `FormatArgsCollector`
     pub fn set(&self, format_args: FxHashMap<Span, FormatArgs>) {
         self.0

tests/ui/uninlined_format_args.fixed

@@ -376,9 +376,10 @@ fn nested_format_args_user() {
     let local_i32 = 1;
     let local_f64 = 2.0;
 
-    // false negative: should warn but currently doesn't because the inner format_args
-    // is not processed when it's used as an argument to another format_args
-    nested_format_args!("{}", local_i32);
-    nested_format_args!("val='{}'", local_i32);
-    nested_format_args!("{:.1}", local_f64);
+    nested_format_args!("{local_i32}");
+    //~^ uninlined_format_args
+    nested_format_args!("val='{local_i32}'");
+    //~^ uninlined_format_args
+    nested_format_args!("{local_f64:.1}");
+    //~^ uninlined_format_args
 }

tests/ui/uninlined_format_args.rs

@@ -381,9 +381,10 @@ fn nested_format_args_user() {
     let local_i32 = 1;
     let local_f64 = 2.0;
 
-    // false negative: should warn but currently doesn't because the inner format_args
-    // is not processed when it's used as an argument to another format_args
     nested_format_args!("{}", local_i32);
+    //~^ uninlined_format_args
     nested_format_args!("val='{}'", local_i32);
+    //~^ uninlined_format_args
     nested_format_args!("{:.1}", local_f64);
+    //~^ uninlined_format_args
 }

tests/ui/uninlined_format_args.stderr

@@ -895,5 +895,41 @@ LL -     usr_println!(true, "{:.1}", local_f64);
 LL +     usr_println!(true, "{local_f64:.1}");
    |
 
-error: aborting due to 75 previous errors
+error: variables can be used directly in the `format!` string
+  --> tests/ui/uninlined_format_args.rs:384:5
+   |
+LL |     nested_format_args!("{}", local_i32);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: change this to
+   |
+LL -     nested_format_args!("{}", local_i32);
+LL +     nested_format_args!("{local_i32}");
+   |
+
+error: variables can be used directly in the `format!` string
+  --> tests/ui/uninlined_format_args.rs:386:5
+   |
+LL |     nested_format_args!("val='{}'", local_i32);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: change this to
+   |
+LL -     nested_format_args!("val='{}'", local_i32);
+LL +     nested_format_args!("val='{local_i32}'");
+   |
+
+error: variables can be used directly in the `format!` string
+  --> tests/ui/uninlined_format_args.rs:388:5
+   |
+LL |     nested_format_args!("{:.1}", local_f64);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: change this to
+   |
+LL -     nested_format_args!("{:.1}", local_f64);
+LL +     nested_format_args!("{local_f64:.1}");
+   |
+
+error: aborting due to 78 previous errors