Restrict SIM105 to try blocks with a body of one simple statement (#1948

)

If a `try` block has multiple statements, a compound statement, or
control flow, rewriting it with `contextlib.suppress` would obfuscate
the fact that the exception still short-circuits further statements in
the block.

Fixes #1947.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

resources/test/fixtures/flake8_simplify/SIM105.py

@@ -41,3 +41,21 @@ def foo():
     pass
 finally:
     print('bar')
+
+try:
+    foo()
+    foo()
+except ValueError:
+    pass
+
+try:
+    for i in range(3):
+        foo()
+except ValueError:
+    pass
+
+def bar():
+    try:
+        return foo()
+    except ValueError:
+        pass

src/checkers/ast.rs

@@ -1384,7 +1384,7 @@ where
                 }
                 if self.settings.rules.enabled(&RuleCode::SIM105) {
                     flake8_simplify::rules::use_contextlib_suppress(
-                        self, stmt, handlers, orelse, finalbody,
+                        self, stmt, body, handlers, orelse, finalbody,
                     );
                 }
                 if self.settings.rules.enabled(&RuleCode::SIM107) {

src/rules/flake8_simplify/rules/use_contextlib_suppress.rs

@@ -1,4 +1,4 @@
-use rustpython_ast::{Excepthandler, ExcepthandlerKind, Stmt, StmtKind};
+use rustpython_ast::{Excepthandler, ExcepthandlerKind, Located, Stmt, StmtKind};
 
 use crate::ast::helpers;
 use crate::ast::types::Range;
@@ -10,11 +10,29 @@ use crate::violations;
 pub fn use_contextlib_suppress(
     checker: &mut Checker,
     stmt: &Stmt,
+    body: &[Stmt],
     handlers: &[Excepthandler],
     orelse: &[Stmt],
     finalbody: &[Stmt],
 ) {
-    if handlers.len() != 1 || !orelse.is_empty() || !finalbody.is_empty() {
+    if !matches!(
+        body,
+        [Located {
+            node: StmtKind::Delete { .. }
+                | StmtKind::Assign { .. }
+                | StmtKind::AugAssign { .. }
+                | StmtKind::AnnAssign { .. }
+                | StmtKind::Assert { .. }
+                | StmtKind::Import { .. }
+                | StmtKind::ImportFrom { .. }
+                | StmtKind::Expr { .. }
+                | StmtKind::Pass,
+            ..
+        }]
+    ) || handlers.len() != 1
+        || !orelse.is_empty()
+        || !finalbody.is_empty()
+    {
         return;
     }
     let handler = &handlers[0];