From 8190ab2557488edab498d633c60636347f90dd7c Mon Sep 17 00:00:00 2001
From: RenzoMXD <170978465+RenzoMXD@users.noreply.github.com>
Date: Mon, 23 Mar 2026 18:37:14 +0100
Subject: [PATCH 1/2] Fix F507 false negative for literal non-tuple RHS in
 %-formatting

---
 .../resources/test/fixtures/pyflakes/F50x.py  | 20 +++++
 .../src/rules/pyflakes/rules/strings.rs       | 22 +++++
 ..._rules__pyflakes__tests__F507_F50x.py.snap | 89 +++++++++++++++++++
 3 files changed, 131 insertions(+)

diff --git a/crates/ruff_linter/resources/test/fixtures/pyflakes/F50x.py b/crates/ruff_linter/resources/test/fixtures/pyflakes/F50x.py
index 692bda5e19a43..7c90dcf68d1cc 100644
--- a/crates/ruff_linter/resources/test/fixtures/pyflakes/F50x.py
+++ b/crates/ruff_linter/resources/test/fixtures/pyflakes/F50x.py
@@ -25,3 +25,23 @@
 '%(k)s' % {**k}
 '%s' % [1, 2, 3]
 '%s' % {1, 2, 3}
+# F507: literal non-tuple RHS with multiple positional placeholders
+'%s %s' % 42  # F507
+'%s %s' % 3.14  # F507
+'%s %s' % "hello"  # F507
+'%s %s' % b"hello"  # F507
+'%s %s' % True  # F507
+'%s %s' % None  # F507
+'%s %s' % ...  # F507
+'%s %s' % f"hello {name}"  # F507
+# ok: single placeholder with literal RHS
+'%s' % 42
+'%s' % "hello"
+'%s' % True
+# ok: variables/expressions could be tuples at runtime
+'%s %s' % banana
+'%s %s' % obj.attr
+'%s %s' % arr[0]
+'%s %s' % get_args()
+'%s %s' % (a if cond else b)
+'%s %s' % (a + b)
diff --git a/crates/ruff_linter/src/rules/pyflakes/rules/strings.rs b/crates/ruff_linter/src/rules/pyflakes/rules/strings.rs
index 9df61638c40f5..59d0fb1bc4776 100644
--- a/crates/ruff_linter/src/rules/pyflakes/rules/strings.rs
+++ b/crates/ruff_linter/src/rules/pyflakes/rules/strings.rs
@@ -757,6 +757,28 @@ pub(crate) fn percent_format_positional_count_mismatch(
                 location,
             );
         }
+    } else if matches!(
+        right,
+        Expr::NumberLiteral(_)
+            | Expr::StringLiteral(_)
+            | Expr::BytesLiteral(_)
+            | Expr::BooleanLiteral(_)
+            | Expr::NoneLiteral(_)
+            | Expr::EllipsisLiteral(_)
+            | Expr::FString(_)
+    ) {
+        // A literal non-tuple right-hand side is always a single positional
+        // argument. Variables, attribute accesses, subscripts, etc. are not
+        // flagged because they could be tuples at runtime.
+        if summary.num_positional != 1 {
+            checker.report_diagnostic(
+                PercentFormatPositionalCountMismatch {
+                    wanted: summary.num_positional,
+                    got: 1,
+                },
+                location,
+            );
+        }
     }
 }
 
diff --git a/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F507_F50x.py.snap b/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F507_F50x.py.snap
index 6528dd1901388..1e2b20c2cd631 100644
--- a/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F507_F50x.py.snap
+++ b/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F507_F50x.py.snap
@@ -1,5 +1,6 @@
 ---
 source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+assertion_line: 192
 ---
 F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
  --> F50x.py:5:1
@@ -22,3 +23,91 @@ F507 `%`-format string has 2 placeholder(s) but 3 substitution(s)
 7 | '%(bar)s' % {}  # F505
 8 | '%(bar)s' % {'bar': 1, 'baz': 2}  # F504
   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:29:1
+   |
+27 | '%s' % {1, 2, 3}
+28 | # F507: literal non-tuple RHS with multiple positional placeholders
+29 | '%s %s' % 42  # F507
+   | ^^^^^^^^^^^^
+30 | '%s %s' % 3.14  # F507
+31 | '%s %s' % "hello"  # F507
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:30:1
+   |
+28 | # F507: literal non-tuple RHS with multiple positional placeholders
+29 | '%s %s' % 42  # F507
+30 | '%s %s' % 3.14  # F507
+   | ^^^^^^^^^^^^^^
+31 | '%s %s' % "hello"  # F507
+32 | '%s %s' % b"hello"  # F507
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:31:1
+   |
+29 | '%s %s' % 42  # F507
+30 | '%s %s' % 3.14  # F507
+31 | '%s %s' % "hello"  # F507
+   | ^^^^^^^^^^^^^^^^^
+32 | '%s %s' % b"hello"  # F507
+33 | '%s %s' % True  # F507
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:32:1
+   |
+30 | '%s %s' % 3.14  # F507
+31 | '%s %s' % "hello"  # F507
+32 | '%s %s' % b"hello"  # F507
+   | ^^^^^^^^^^^^^^^^^^
+33 | '%s %s' % True  # F507
+34 | '%s %s' % None  # F507
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:33:1
+   |
+31 | '%s %s' % "hello"  # F507
+32 | '%s %s' % b"hello"  # F507
+33 | '%s %s' % True  # F507
+   | ^^^^^^^^^^^^^^
+34 | '%s %s' % None  # F507
+35 | '%s %s' % ...  # F507
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:34:1
+   |
+32 | '%s %s' % b"hello"  # F507
+33 | '%s %s' % True  # F507
+34 | '%s %s' % None  # F507
+   | ^^^^^^^^^^^^^^
+35 | '%s %s' % ...  # F507
+36 | '%s %s' % f"hello {name}"  # F507
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:35:1
+   |
+33 | '%s %s' % True  # F507
+34 | '%s %s' % None  # F507
+35 | '%s %s' % ...  # F507
+   | ^^^^^^^^^^^^^
+36 | '%s %s' % f"hello {name}"  # F507
+37 | # ok: single placeholder with literal RHS
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:36:1
+   |
+34 | '%s %s' % None  # F507
+35 | '%s %s' % ...  # F507
+36 | '%s %s' % f"hello {name}"  # F507
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+37 | # ok: single placeholder with literal RHS
+38 | '%s' % 42
+   |

From e802e57df52376eba42dfe62e1f9a6c94c582d09 Mon Sep 17 00:00:00 2001
From: RenzoMXD <170978465+RenzoMXD@users.noreply.github.com>
Date: Tue, 24 Mar 2026 15:07:17 +0100
Subject: [PATCH 2/2] Use ResolvedPythonType for F507 non-tuple RHS detection

---
 .../resources/test/fixtures/pyflakes/F50x.py  |  7 ++
 .../src/rules/pyflakes/rules/strings.rs       | 21 ++---
 ..._rules__pyflakes__tests__F507_F50x.py.snap | 82 ++++++++++++++++++-
 3 files changed, 93 insertions(+), 17 deletions(-)

diff --git a/crates/ruff_linter/resources/test/fixtures/pyflakes/F50x.py b/crates/ruff_linter/resources/test/fixtures/pyflakes/F50x.py
index 7c90dcf68d1cc..4119de68ebaa2 100644
--- a/crates/ruff_linter/resources/test/fixtures/pyflakes/F50x.py
+++ b/crates/ruff_linter/resources/test/fixtures/pyflakes/F50x.py
@@ -34,6 +34,12 @@
 '%s %s' % None  # F507
 '%s %s' % ...  # F507
 '%s %s' % f"hello {name}"  # F507
+# F507: ResolvedPythonType catches compound expressions with known types
+'%s %s' % -1  # F507 (unary op on int → int)
+'%s %s' % (1 + 2)  # F507 (int + int → int)
+'%s %s' % (not x)  # F507 (not → bool)
+'%s %s' % ("a" + "b")  # F507 (str + str → str)
+'%s %s' % (1 if True else 2)  # F507 (int if ... else int → int)
 # ok: single placeholder with literal RHS
 '%s' % 42
 '%s' % "hello"
@@ -43,5 +49,6 @@
 '%s %s' % obj.attr
 '%s %s' % arr[0]
 '%s %s' % get_args()
+# ok: ternary/binop where one branch could be a tuple → Unknown
 '%s %s' % (a if cond else b)
 '%s %s' % (a + b)
diff --git a/crates/ruff_linter/src/rules/pyflakes/rules/strings.rs b/crates/ruff_linter/src/rules/pyflakes/rules/strings.rs
index 59d0fb1bc4776..4c5e1140434b2 100644
--- a/crates/ruff_linter/src/rules/pyflakes/rules/strings.rs
+++ b/crates/ruff_linter/src/rules/pyflakes/rules/strings.rs
@@ -2,6 +2,7 @@ use std::string::ToString;
 
 use ruff_diagnostics::Applicability;
 use ruff_python_ast::helpers::contains_effect;
+use ruff_python_semantic::analyze::type_inference::{PythonType, ResolvedPythonType};
 use rustc_hash::FxHashSet;
 
 use ruff_macros::{ViolationMetadata, derive_message_formats};
@@ -757,20 +758,12 @@ pub(crate) fn percent_format_positional_count_mismatch(
                 location,
             );
         }
-    } else if matches!(
-        right,
-        Expr::NumberLiteral(_)
-            | Expr::StringLiteral(_)
-            | Expr::BytesLiteral(_)
-            | Expr::BooleanLiteral(_)
-            | Expr::NoneLiteral(_)
-            | Expr::EllipsisLiteral(_)
-            | Expr::FString(_)
-    ) {
-        // A literal non-tuple right-hand side is always a single positional
-        // argument. Variables, attribute accesses, subscripts, etc. are not
-        // flagged because they could be tuples at runtime.
-        if summary.num_positional != 1 {
+    } else if let ResolvedPythonType::Atom(resolved_type) = ResolvedPythonType::from(right) {
+        // If we can infer a concrete non-tuple type for the RHS, it's always
+        // a single positional argument. Variables, attribute accesses, calls,
+        // etc. resolve to `Unknown` and are not flagged because they could be
+        // tuples at runtime.
+        if resolved_type != PythonType::Tuple && summary.num_positional != 1 {
             checker.report_diagnostic(
                 PercentFormatPositionalCountMismatch {
                     wanted: summary.num_positional,
diff --git a/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F507_F50x.py.snap b/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F507_F50x.py.snap
index 1e2b20c2cd631..0989f6c0e3f74 100644
--- a/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F507_F50x.py.snap
+++ b/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F507_F50x.py.snap
@@ -24,6 +24,27 @@ F507 `%`-format string has 2 placeholder(s) but 3 substitution(s)
 8 | '%(bar)s' % {'bar': 1, 'baz': 2}  # F504
   |
 
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:10:1
+   |
+ 8 | '%(bar)s' % {'bar': 1, 'baz': 2}  # F504
+ 9 | '%(bar)s' % (1, 2, 3)  # F502
+10 | '%s %s' % {'k': 'v'}  # F503
+   | ^^^^^^^^^^^^^^^^^^^^
+11 | '%(bar)*s' % {'bar': 'baz'}  # F506, F508
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:22:1
+   |
+20 | # ok *args and **kwargs
+21 | a = []
+22 | '%s %s' % [*a]
+   | ^^^^^^^^^^^^^^
+23 | '%s %s' % (*a,)
+24 | k = {}
+   |
+
 F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
   --> F50x.py:29:1
    |
@@ -98,7 +119,7 @@ F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
 35 | '%s %s' % ...  # F507
    | ^^^^^^^^^^^^^
 36 | '%s %s' % f"hello {name}"  # F507
-37 | # ok: single placeholder with literal RHS
+37 | # F507: ResolvedPythonType catches compound expressions with known types
    |
 
 F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
@@ -108,6 +129,61 @@ F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
 35 | '%s %s' % ...  # F507
 36 | '%s %s' % f"hello {name}"  # F507
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
-37 | # ok: single placeholder with literal RHS
-38 | '%s' % 42
+37 | # F507: ResolvedPythonType catches compound expressions with known types
+38 | '%s %s' % -1  # F507 (unary op on int → int)
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:38:1
+   |
+36 | '%s %s' % f"hello {name}"  # F507
+37 | # F507: ResolvedPythonType catches compound expressions with known types
+38 | '%s %s' % -1  # F507 (unary op on int → int)
+   | ^^^^^^^^^^^^
+39 | '%s %s' % (1 + 2)  # F507 (int + int → int)
+40 | '%s %s' % (not x)  # F507 (not → bool)
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:39:1
+   |
+37 | # F507: ResolvedPythonType catches compound expressions with known types
+38 | '%s %s' % -1  # F507 (unary op on int → int)
+39 | '%s %s' % (1 + 2)  # F507 (int + int → int)
+   | ^^^^^^^^^^^^^^^^^
+40 | '%s %s' % (not x)  # F507 (not → bool)
+41 | '%s %s' % ("a" + "b")  # F507 (str + str → str)
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:40:1
+   |
+38 | '%s %s' % -1  # F507 (unary op on int → int)
+39 | '%s %s' % (1 + 2)  # F507 (int + int → int)
+40 | '%s %s' % (not x)  # F507 (not → bool)
+   | ^^^^^^^^^^^^^^^^^
+41 | '%s %s' % ("a" + "b")  # F507 (str + str → str)
+42 | '%s %s' % (1 if True else 2)  # F507 (int if ... else int → int)
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:41:1
+   |
+39 | '%s %s' % (1 + 2)  # F507 (int + int → int)
+40 | '%s %s' % (not x)  # F507 (not → bool)
+41 | '%s %s' % ("a" + "b")  # F507 (str + str → str)
+   | ^^^^^^^^^^^^^^^^^^^^^
+42 | '%s %s' % (1 if True else 2)  # F507 (int if ... else int → int)
+43 | # ok: single placeholder with literal RHS
+   |
+
+F507 `%`-format string has 2 placeholder(s) but 1 substitution(s)
+  --> F50x.py:42:1
+   |
+40 | '%s %s' % (not x)  # F507 (not → bool)
+41 | '%s %s' % ("a" + "b")  # F507 (str + str → str)
+42 | '%s %s' % (1 if True else 2)  # F507 (int if ... else int → int)
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+43 | # ok: single placeholder with literal RHS
+44 | '%s' % 42
    |