De-duplicate SIM102 (#2050)

The idea is the same as #1867. Avoids emitting `SIM102` twice for the following code:

```python
if a:
    if b:
        if c:
            d
```

```
resources/test/fixtures/flake8_simplify/SIM102.py:1:1: SIM102 Use a single `if` statement instead of nested `if` statements
resources/test/fixtures/flake8_simplify/SIM102.py:2:5: SIM102 Use a single `if` statement instead of nested `if` statements
```

resources/test/fixtures/flake8_simplify/SIM102.py

@@ -3,6 +3,12 @@ if a:
     if b:
         c
 
+# SIM102
+if a:
+    if b:
+        if c:
+            d
+
 # SIM102
 if a:
     pass

src/checkers/ast.rs

@@ -1359,7 +1359,13 @@ where
                     flake8_type_checking::rules::empty_type_checking_block(self, test, body);
                 }
                 if self.settings.rules.enabled(&Rule::NestedIfStatements) {
-                    flake8_simplify::rules::nested_if_statements(self, stmt);
+                    flake8_simplify::rules::nested_if_statements(
+                        self,
+                        stmt,
+                        test,
+                        body,
+                        self.current_stmt_parent().map(Into::into),
+                    );
                 }
                 if self
                     .settings

src/rules/flake8_simplify/rules/ast_if.rs

@@ -3,8 +3,8 @@ use rustpython_ast::{Cmpop, Constant, Expr, ExprContext, ExprKind, Stmt, StmtKin
 
 use crate::ast::comparable::ComparableExpr;
 use crate::ast::helpers::{
-    contains_call_path, contains_effect, create_expr, create_stmt, has_comments_in, unparse_expr,
-    unparse_stmt,
+    contains_call_path, contains_effect, create_expr, create_stmt, first_colon_range,
+    has_comments_in, unparse_expr, unparse_stmt,
 };
 use crate::ast::types::Range;
 use crate::checkers::ast::Checker;
@@ -37,36 +37,64 @@ fn is_main_check(expr: &Expr) -> bool {
     false
 }
 
+/// Find the last nested if statement and return the test expression and the
+/// first statement.
+///
+/// ```python
+/// if xxx:
+///     if yyy:
+///      # ^^^ returns this expression
+///         z = 1
+///       # ^^^^^ and this statement
+///         ...
+/// ```
+fn find_last_nested_if(body: &[Stmt]) -> Option<(&Expr, &Stmt)> {
+    let [Stmt { node: StmtKind::If { test, body: inner_body, orelse }, ..}] = body else { return None };
+    if !(orelse.is_empty() && body.len() == 1) {
+        return None;
+    }
+    find_last_nested_if(inner_body).or_else(|| {
+        Some((
+            test,
+            inner_body.last().expect("Expected body to be non-empty"),
+        ))
+    })
+}
+
 /// 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;
-    };
-
+pub fn nested_if_statements(
+    checker: &mut Checker,
+    stmt: &Stmt,
+    test: &Expr,
+    body: &[Stmt],
+    parent: Option<&Stmt>,
+) {
     if is_main_check(test) {
         return;
     }
 
-    let mut diagnostic = Diagnostic::new(violations::NestedIfStatements, Range::from_located(stmt));
+    if let Some(parent) = parent {
+        if let StmtKind::If { body, orelse, .. } = &parent.node {
+            if orelse.is_empty() && body.len() == 1 {
+                return;
+            }
+        }
+    }
+
+    let Some((test, first_stmt)) = find_last_nested_if(body) else {
+        return;
+    };
+    let colon = first_colon_range(
+        Range::new(test.end_location.unwrap(), first_stmt.location),
+        checker.locator,
+    );
+    let mut diagnostic = Diagnostic::new(
+        violations::NestedIfStatements,
+        colon.map_or_else(
+            || Range::from_located(stmt),
+            |colon| Range::new(stmt.location, colon.end_location),
+        ),
+    );
     if checker.patch(&Rule::NestedIfStatements) {
         // The fixer preserves comments in the nested body, but removes comments between
         // the outer and inner if statements.

src/rules/flake8_simplify/snapshots/ruff__rules__flake8_simplify__tests__SIM102_SIM102.py.snap

@@ -8,7 +8,7 @@ expression: diagnostics
     row: 2
     column: 0
   end_location:
-    row: 4
+    row: 3
     column: 9
   fix:
     content: "if a and b:\n    c\n"
@@ -22,29 +22,36 @@ expression: diagnostics
 - kind:
     NestedIfStatements: ~
   location:
-    row: 9
+    row: 7
     column: 0
   end_location:
-    row: 11
-    column: 9
+    row: 9
+    column: 13
   fix:
-    content: "elif b and c:\n    d\n"
+    content: "if a and b:\n    if c:\n        d\n"
     location:
-      row: 9
+      row: 7
       column: 0
     end_location:
-      row: 12
+      row: 11
       column: 0
   parent: ~
 - kind:
     NestedIfStatements: ~
   location:
-    row: 14
+    row: 15
     column: 0
   end_location:
-    row: 17
+    row: 16
     column: 9
-  fix: ~
+  fix:
+    content: "elif b and c:\n    d\n"
+    location:
+      row: 15
+      column: 0
+    end_location:
+      row: 18
+      column: 0
   parent: ~
 - kind:
     NestedIfStatements: ~
@@ -52,83 +59,93 @@ expression: diagnostics
     row: 20
     column: 0
   end_location:
-    row: 23
+    row: 22
+    column: 9
+  fix: ~
+  parent: ~
+- kind:
+    NestedIfStatements: ~
+  location:
+    row: 26
+    column: 0
+  end_location:
+    row: 27
     column: 9
   fix:
     content: "if a and b:\n    # Fixable due to placement of this comment.\n    c\n"
     location:
-      row: 20
+      row: 26
       column: 0
     end_location:
-      row: 24
+      row: 30
       column: 0
   parent: ~
 - kind:
     NestedIfStatements: ~
   location:
-    row: 45
+    row: 51
     column: 4
   end_location:
-    row: 57
-    column: 23
+    row: 52
+    column: 16
   fix:
     content: "    if True and True:\n        \"\"\"this\nis valid\"\"\"\n\n        \"\"\"the indentation on\n            this line is significant\"\"\"\n\n        \"this is\" \\\n\"allowed too\"\n\n        (\"so is\"\n\"this for some reason\")\n"
     location:
-      row: 45
+      row: 51
       column: 0
     end_location:
-      row: 58
+      row: 64
       column: 0
   parent: ~
 - kind:
     NestedIfStatements: ~
   location:
-    row: 61
+    row: 67
     column: 0
   end_location:
-    row: 73
-    column: 23
+    row: 68
+    column: 12
   fix:
     content: "if True and True:\n    \"\"\"this\nis valid\"\"\"\n\n    \"\"\"the indentation on\n        this line is significant\"\"\"\n\n    \"this is\" \\\n\"allowed too\"\n\n    (\"so is\"\n\"this for some reason\")\n"
     location:
-      row: 61
+      row: 67
       column: 0
     end_location:
-      row: 74
+      row: 80
       column: 0
   parent: ~
 - kind:
     NestedIfStatements: ~
   location:
-    row: 77
+    row: 83
     column: 4
   end_location:
-    row: 81
-    column: 32
+    row: 86
+    column: 10
   fix:
     content: "    if node.module and (node.module == \"multiprocessing\" or node.module.startswith(\n        \"multiprocessing.\"\n    )):\n        print(\"Bad module!\")\n"
     location:
-      row: 77
+      row: 83
       column: 0
     end_location:
-      row: 82
+      row: 88
       column: 0
   parent: ~
 - kind:
     NestedIfStatements: ~
   location:
-    row: 84
+    row: 90
     column: 0
   end_location:
-    row: 88
-    column: 28
+    row: 93
+    column: 6
   fix:
     content: "if node.module and (node.module == \"multiprocessing\" or node.module.startswith(\n    \"multiprocessing.\"\n)):\n    print(\"Bad module!\")\n"
     location:
-      row: 84
+      row: 90
       column: 0
     end_location:
-      row: 89
+      row: 95
       column: 0
   parent: ~