Got some basic stuff in

resources/test/fixtures/pyupgrade/UP031.py

@@ -0,0 +1,3 @@
+'%s %s' % (a, b)
+
+# Make sure to include assignment and inside a call, also multi-line

src/checkers/ast.rs

@@ -2589,6 +2589,9 @@ where
                             }
                         }
                     }
+                    if self.settings.enabled.contains(&RuleCode::UP031) {
+                        pyupgrade::rules::printf_string_formatting(self, left, right);
+                    }
                 }
             }
             ExprKind::BinOp {

src/pyupgrade/rules/mod.rs

@@ -30,6 +30,7 @@ pub(crate) use use_pep585_annotation::use_pep585_annotation;
 pub(crate) use use_pep604_annotation::use_pep604_annotation;
 pub(crate) use useless_metaclass_type::useless_metaclass_type;
 pub(crate) use useless_object_inheritance::useless_object_inheritance;
+pub(crate) use printf_string_formatting::printf_string_formatting;
 
 use crate::ast::helpers::{self};
 use crate::ast::types::{Range, Scope, ScopeKind};
@@ -65,6 +66,7 @@ mod use_pep585_annotation;
 mod use_pep604_annotation;
 mod useless_metaclass_type;
 mod useless_object_inheritance;
+mod printf_string_formatting;
 
 /// UP008
 pub fn super_args(

src/pyupgrade/rules/printf_string_formatting.rs

@@ -0,0 +1,9 @@
+use crate::checkers::ast::Checker;
+use rustpython_ast::Expr;
+
+/// UP031
+pub fn printf_string_formatting(checker: &mut Checker, left: &Expr, right: &Expr) {
+    println!("{:?}", left);
+    println!("==========");
+    println!("{:?}", right);
+}

src/registry.rs

@@ -347,6 +347,7 @@ define_rule_mapping!(
     UP028 => violations::RewriteYieldFrom,
     UP029 => violations::UnnecessaryBuiltinImport,
     UP030 => violations::FormatLiterals,
+    UP031 => violations::PrintfStringFormatting,
     // pydocstyle
     D100 => violations::PublicModule,
     D101 => violations::PublicClass,

src/violations.rs

@@ -3486,6 +3486,25 @@ impl AlwaysAutofixableViolation for ReplaceUniversalNewlines {
     }
 }
 
+define_violation!(
+    pub struct PrintfStringFormatting;
+);
+impl AlwaysAutofixableViolation for PrintfStringFormatting {
+    fn message(&self) -> String {
+        "Use builtin `open`".to_string()
+    }
+
+    fn autofix_title(&self) -> String {
+        "Replace with builtin `open`".to_string()
+    }
+
+    fn placeholder() -> Self {
+        // FOR REVIEWER: Should we switch all of these to self? Is there any way to do this automatically when
+        // defining the trait (im pretty sure the answer is no, but I want to confirm)
+        Self
+    }
+}
+
 define_violation!(
     pub struct ReplaceStdoutStderr;
 );