From d6c1146c730a2d3500d3b43ac014d7087ad8e3fd Mon Sep 17 00:00:00 2001
From: Charlie Marsh <charlie.r.marsh@gmail.com>
Date: Sat, 2 Mar 2024 19:18:42 -0500
Subject: [PATCH] Avoid false-positives for parens-on-raise with
 futures.exception()

---
 .../test/fixtures/flake8_raise/RSE102.py      | 12 +++++++
 .../unnecessary_paren_on_raise_exception.rs   | 33 +++++++++++++++----
 ...ry-paren-on-raise-exception_RSE102.py.snap | 14 ++++++++
 3 files changed, 53 insertions(+), 6 deletions(-)

diff --git a/crates/ruff_linter/resources/test/fixtures/flake8_raise/RSE102.py b/crates/ruff_linter/resources/test/fixtures/flake8_raise/RSE102.py
index bba0e98b17caf4..0d737c8ca4fb07 100644
--- a/crates/ruff_linter/resources/test/fixtures/flake8_raise/RSE102.py
+++ b/crates/ruff_linter/resources/test/fixtures/flake8_raise/RSE102.py
@@ -93,3 +93,15 @@ def func():
 
 # OK
 raise func()
+
+
+# OK
+future = executor.submit(float, "a")
+if future.exception():
+    raise future.exception()
+
+
+# RSE102
+future = executor.submit(float, "a")
+if future.exception():
+    raise future.Exception()
diff --git a/crates/ruff_linter/src/rules/flake8_raise/rules/unnecessary_paren_on_raise_exception.rs b/crates/ruff_linter/src/rules/flake8_raise/rules/unnecessary_paren_on_raise_exception.rs
index a056bbc755f8d1..c64e7132e522a3 100644
--- a/crates/ruff_linter/src/rules/flake8_raise/rules/unnecessary_paren_on_raise_exception.rs
+++ b/crates/ruff_linter/src/rules/flake8_raise/rules/unnecessary_paren_on_raise_exception.rs
@@ -76,17 +76,38 @@ pub(crate) fn unnecessary_paren_on_raise_exception(checker: &mut Checker, expr:
             None
         };
 
-        // `ctypes.WinError()` is a function, not a class. It's part of the standard library, so
-        // we might as well get it right.
-        if exception_type.is_none()
-            && checker
+        if exception_type.is_none() {
+            // If the method name doesn't _look_ like a class (i.e., it's lowercase), it's
+            // probably a function call, not a class.
+            let identifier = match func.as_ref() {
+                Expr::Name(ast::ExprName { id, .. }) => Some(id.as_str()),
+                Expr::Attribute(ast::ExprAttribute { attr, .. }) => Some(attr.as_str()),
+                _ => None,
+            };
+            if identifier.is_some_and(|identifier| {
+                identifier
+                    .strip_prefix('_')
+                    .unwrap_or_else(|| identifier)
+                    .chars()
+                    .next()
+                    .is_some_and(char::is_lowercase)
+            }) {
+                return;
+            }
+
+            // `ctypes.WinError()` is a function, not a class. It's part of the standard library, so
+            // we might as well get it right.
+            if checker
                 .semantic()
                 .resolve_call_path(func)
                 .is_some_and(|call_path| matches!(call_path.as_slice(), ["ctypes", "WinError"]))
-        {
-            return;
+            {
+                return;
+            }
         }
 
+        // If the
+
         let mut diagnostic = Diagnostic::new(UnnecessaryParenOnRaiseException, arguments.range());
 
         // If the arguments are immediately followed by a `from`, insert whitespace to avoid
diff --git a/crates/ruff_linter/src/rules/flake8_raise/snapshots/ruff_linter__rules__flake8_raise__tests__unnecessary-paren-on-raise-exception_RSE102.py.snap b/crates/ruff_linter/src/rules/flake8_raise/snapshots/ruff_linter__rules__flake8_raise__tests__unnecessary-paren-on-raise-exception_RSE102.py.snap
index d1d89829c673f2..d0dd2b4084b53d 100644
--- a/crates/ruff_linter/src/rules/flake8_raise/snapshots/ruff_linter__rules__flake8_raise__tests__unnecessary-paren-on-raise-exception_RSE102.py.snap
+++ b/crates/ruff_linter/src/rules/flake8_raise/snapshots/ruff_linter__rules__flake8_raise__tests__unnecessary-paren-on-raise-exception_RSE102.py.snap
@@ -281,4 +281,18 @@ RSE102.py:84:10: RSE102 [*] Unnecessary parentheses on raised exception
 86 86 | # OK
 87 87 | raise ctypes.WinError()
 
+RSE102.py:107:27: RSE102 [*] Unnecessary parentheses on raised exception
+    |
+105 | future = executor.submit(float, "a")
+106 | if future.exception():
+107 |     raise future.Exception()
+    |                           ^^ RSE102
+    |
+    = help: Remove unnecessary parentheses
 
+ℹ Unsafe fix
+104 104 | # RSE102
+105 105 | future = executor.submit(float, "a")
+106 106 | if future.exception():
+107     |-    raise future.Exception()
+    107 |+    raise future.Exception