Implement nested-if detection

README.md

@@ -964,6 +964,7 @@ For more, see [flake8-simplify](https://pypi.org/project/flake8-simplify/0.19.3/
 
 | Code | Name | Message | Fix |
 | ---- | ---- | ------- | --- |
+| SIM102 | NestedIfStatements | Use a single if-statement instead of nested if-statements |  |
 | SIM105 | UseContextlibSuppress | Use `contextlib.suppress(...)` instead of try-except-pass |  |
 | SIM118 | KeyInDict | Use `key in dict` instead of `key in dict.keys()` | 🛠 |
 | SIM220 | AAndNotA | Use `False` instead of `... and not ...` | 🛠 |

resources/test/fixtures/flake8_simplify/SIM102.py

@@ -0,0 +1,25 @@
+if a:  # SIM102
+    if b:
+        c
+
+
+if a:
+    pass
+elif b:  # SIM102
+    if c:
+        d
+
+if a:
+    if b:
+        c
+    else:
+        d
+
+if __name__ == "__main__":
+    if foo():
+        ...
+
+if a:
+    d
+    if b:
+        c

src/checkers/ast.rs

@@ -1177,6 +1177,9 @@ where
                 if self.settings.enabled.contains(&CheckCode::F634) {
                     pyflakes::plugins::if_tuple(self, stmt, test);
                 }
+                if self.settings.enabled.contains(&CheckCode::SIM102) {
+                    flake8_simplify::plugins::nested_if_statements(self, stmt);
+                }
             }
             StmtKind::Assert { test, msg } => {
                 if self.settings.enabled.contains(&CheckCode::F631) {

src/flake8_simplify/mod.rs

@@ -19,6 +19,7 @@ mod tests {
     #[test_case(CheckCode::SIM300, Path::new("SIM300.py"); "SIM300")]
     #[test_case(CheckCode::SIM221, Path::new("SIM221.py"); "SIM221")]
     #[test_case(CheckCode::SIM220, Path::new("SIM220.py"); "SIM220")]
+    #[test_case(CheckCode::SIM102, Path::new("SIM102.py"); "SIM102")]
     fn checks(check_code: CheckCode, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", check_code.as_ref(), path.to_string_lossy());
         let checks = test_path(

src/flake8_simplify/plugins/ast_if.rs

@@ -0,0 +1,64 @@
+use rustpython_ast::{Constant, Expr, ExprKind, Stmt, StmtKind};
+
+use crate::ast::types::Range;
+use crate::checkers::ast::Checker;
+use crate::registry::{Check, CheckKind};
+
+fn is_main_check(expr: &Expr) -> bool {
+    if let ExprKind::Compare {
+        left, comparators, ..
+    } = &expr.node
+    {
+        if let ExprKind::Name { id, .. } = &left.node {
+            if id == "__name__" {
+                if comparators.len() == 1 {
+                    if let ExprKind::Constant {
+                        value: Constant::Str(value),
+                        ..
+                    } = &comparators[0].node
+                    {
+                        if value == "__main__" {
+                            return true;
+                        }
+                    }
+                }
+            }
+        }
+    }
+    false
+}
+
+/// SIM102
+pub fn nested_if_statements(checker: &mut Checker, stmt: &Stmt) {
+    let StmtKind::If { test, body, orelse } = &stmt.node else {
+        return;
+    };
+
+    // if a: <---
+    //     if b: <---
+    //         c
+    let is_nested_if = {
+        if orelse.is_empty() && body.len() == 1 {
+            if let StmtKind::If { orelse, .. } = &body[0].node {
+                orelse.is_empty()
+            } else {
+                false
+            }
+        } else {
+            false
+        }
+    };
+
+    if !is_nested_if {
+        return;
+    };
+
+    if is_main_check(test) {
+        return;
+    }
+
+    checker.add_check(Check::new(
+        CheckKind::NestedIfStatements,
+        Range::from_located(stmt),
+    ));
+}

src/flake8_simplify/plugins/mod.rs

@@ -1,9 +1,11 @@
-pub use bool_ops::{a_and_not_a, a_or_not_a, and_false, or_true};
+pub use ast_bool_op::{a_and_not_a, a_or_not_a, and_false, or_true};
+pub use ast_if::nested_if_statements;
 pub use key_in_dict::{key_in_dict_compare, key_in_dict_for};
 pub use use_contextlib_suppress::use_contextlib_suppress;
 pub use yoda_conditions::yoda_conditions;
 
-mod bool_ops;
+mod ast_bool_op;
+mod ast_if;
 mod key_in_dict;
 mod use_contextlib_suppress;
 mod yoda_conditions;

src/flake8_simplify/snapshots/ruff__flake8_simplify__tests__SIM102_SIM102.py.snap

@@ -0,0 +1,23 @@
+---
+source: src/flake8_simplify/mod.rs
+expression: checks
+---
+- kind: NestedIfStatements
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 3
+    column: 9
+  fix: ~
+  parent: ~
+- kind: NestedIfStatements
+  location:
+    row: 8
+    column: 0
+  end_location:
+    row: 10
+    column: 9
+  fix: ~
+  parent: ~
+

src/registry.rs

@@ -217,6 +217,7 @@ pub enum CheckCode {
     YTT302,
     YTT303,
     // flake8-simplify
+    SIM102,
     SIM105,
     SIM118,
     SIM220,
@@ -951,6 +952,7 @@ pub enum CheckKind {
     SysVersionCmpStr10,
     SysVersionSlice1Referenced,
     // flake8-simplify
+    NestedIfStatements,
     AAndNotA(String),
     AOrNotA(String),
     KeyInDict(String, String),
@@ -1383,6 +1385,7 @@ impl CheckCode {
             // flake8-blind-except
             CheckCode::BLE001 => CheckKind::BlindExcept("Exception".to_string()),
             // flake8-simplify
+            CheckCode::SIM102 => CheckKind::NestedIfStatements,
             CheckCode::SIM105 => CheckKind::UseContextlibSuppress("...".to_string()),
             CheckCode::SIM118 => CheckKind::KeyInDict("key".to_string(), "dict".to_string()),
             CheckCode::SIM220 => CheckKind::AAndNotA("...".to_string()),
@@ -1914,6 +1917,7 @@ impl CheckCode {
             CheckCode::S106 => CheckCategory::Flake8Bandit,
             CheckCode::S107 => CheckCategory::Flake8Bandit,
             // flake8-simplify
+            CheckCode::SIM102 => CheckCategory::Flake8Simplify,
             CheckCode::SIM105 => CheckCategory::Flake8Simplify,
             CheckCode::SIM118 => CheckCategory::Flake8Simplify,
             CheckCode::SIM220 => CheckCategory::Flake8Simplify,
@@ -2167,6 +2171,7 @@ impl CheckKind {
             CheckKind::SysVersionCmpStr10 => &CheckCode::YTT302,
             CheckKind::SysVersionSlice1Referenced => &CheckCode::YTT303,
             // flake8-simplify
+            CheckKind::NestedIfStatements => &CheckCode::SIM102,
             CheckKind::UseContextlibSuppress(..) => &CheckCode::SIM105,
             CheckKind::KeyInDict(..) => &CheckCode::SIM118,
             CheckKind::AAndNotA(..) => &CheckCode::SIM220,
@@ -2930,6 +2935,9 @@ impl CheckKind {
                 "`sys.version[:1]` referenced (python10), use `sys.version_info`".to_string()
             }
             // flake8-simplify
+            CheckKind::NestedIfStatements => {
+                "Use a single if-statement instead of nested if-statements".to_string()
+            }
             CheckKind::KeyInDict(key, dict) => {
                 format!("Use `{key} in {dict}` instead of `{key} in {dict}.keys()`")
             }

src/registry_gen.rs

@@ -517,6 +517,7 @@ pub enum CheckCodePrefix {
     SIM,
     SIM1,
     SIM10,
+    SIM102,
     SIM105,
     SIM11,
     SIM118,
@@ -805,6 +806,7 @@ impl CheckCodePrefix {
                 CheckCode::YTT301,
                 CheckCode::YTT302,
                 CheckCode::YTT303,
+                CheckCode::SIM102,
                 CheckCode::SIM105,
                 CheckCode::SIM118,
                 CheckCode::SIM220,
@@ -2623,6 +2625,7 @@ impl CheckCodePrefix {
             CheckCodePrefix::S106 => vec![CheckCode::S106],
             CheckCodePrefix::S107 => vec![CheckCode::S107],
             CheckCodePrefix::SIM => vec![
+                CheckCode::SIM102,
                 CheckCode::SIM105,
                 CheckCode::SIM118,
                 CheckCode::SIM220,
@@ -2631,8 +2634,9 @@ impl CheckCodePrefix {
                 CheckCode::SIM223,
                 CheckCode::SIM300,
             ],
-            CheckCodePrefix::SIM1 => vec![CheckCode::SIM105, CheckCode::SIM118],
-            CheckCodePrefix::SIM10 => vec![CheckCode::SIM105],
+            CheckCodePrefix::SIM1 => vec![CheckCode::SIM102, CheckCode::SIM105, CheckCode::SIM118],
+            CheckCodePrefix::SIM10 => vec![CheckCode::SIM102, CheckCode::SIM105],
+            CheckCodePrefix::SIM102 => vec![CheckCode::SIM102],
             CheckCodePrefix::SIM105 => vec![CheckCode::SIM105],
             CheckCodePrefix::SIM11 => vec![CheckCode::SIM118],
             CheckCodePrefix::SIM118 => vec![CheckCode::SIM118],
@@ -3605,6 +3609,7 @@ impl CheckCodePrefix {
             CheckCodePrefix::SIM => SuffixLength::Zero,
             CheckCodePrefix::SIM1 => SuffixLength::One,
             CheckCodePrefix::SIM10 => SuffixLength::Two,
+            CheckCodePrefix::SIM102 => SuffixLength::Three,
             CheckCodePrefix::SIM105 => SuffixLength::Three,
             CheckCodePrefix::SIM11 => SuffixLength::Two,
             CheckCodePrefix::SIM118 => SuffixLength::Three,