From b1eaf0e75ef9749f51e5aef1333790753c94a779 Mon Sep 17 00:00:00 2001
From: Brent Westbrook <brentrwestbrook@gmail.com>
Date: Thu, 27 Feb 2025 17:05:15 -0500
Subject: [PATCH 1/3] reproduce issue

---
 crates/ruff/tests/lint.rs | 44 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/crates/ruff/tests/lint.rs b/crates/ruff/tests/lint.rs
index 15591314ce2bae..d3e2f5d767ea13 100644
--- a/crates/ruff/tests/lint.rs
+++ b/crates/ruff/tests/lint.rs
@@ -2701,3 +2701,47 @@ match 2:
     "
     );
 }
+
+/// Regression test for <https://github.com/astral-sh/ruff/issues/16417>
+#[test]
+fn cache_syntax_errors() -> Result<()> {
+    let tempdir = TempDir::new()?;
+    fs::write(tempdir.path().join("main.py"), "match 2:\n    case 1: ...")?;
+
+    let mut cmd = Command::new(get_cargo_bin(BIN_NAME));
+    // inline STDIN_BASE_OPTIONS to remove --no-cache
+    cmd.args(["check", "--output-format", "concise"])
+        .arg("--target-version=py39")
+        .arg("--preview")
+        .current_dir(&tempdir);
+
+    assert_cmd_snapshot!(
+        cmd,
+        @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    main.py:1:1: SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)
+    Found 1 error.
+
+    ----- stderr -----
+    warning: Detected debug build without --no-cache.
+    "
+    );
+
+    // this should *not* be cached, like normal parse errors
+    assert_cmd_snapshot!(
+        cmd,
+        @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    All checks passed!
+
+    ----- stderr -----
+    warning: Detected debug build without --no-cache.
+    "
+    );
+
+    Ok(())
+}

From e920515e9fcdb16eb048507957ee0447e919a257 Mon Sep 17 00:00:00 2001
From: Brent Westbrook <brentrwestbrook@gmail.com>
Date: Thu, 27 Feb 2025 17:14:43 -0500
Subject: [PATCH 2/3] check for unsupported_syntax_errors in has_syntax_error

---
 crates/ruff/tests/lint.rs        | 7 ++++---
 crates/ruff_linter/src/linter.rs | 4 ++--
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/crates/ruff/tests/lint.rs b/crates/ruff/tests/lint.rs
index d3e2f5d767ea13..1add511de6af35 100644
--- a/crates/ruff/tests/lint.rs
+++ b/crates/ruff/tests/lint.rs
@@ -2733,10 +2733,11 @@ fn cache_syntax_errors() -> Result<()> {
     assert_cmd_snapshot!(
         cmd,
         @r"
-    success: true
-    exit_code: 0
+    success: false
+    exit_code: 1
     ----- stdout -----
-    All checks passed!
+    main.py:1:1: SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)
+    Found 1 error.
 
     ----- stderr -----
     warning: Detected debug build without --no-cache.
diff --git a/crates/ruff_linter/src/linter.rs b/crates/ruff_linter/src/linter.rs
index be0362f9b1244b..51dfec63b58d38 100644
--- a/crates/ruff_linter/src/linter.rs
+++ b/crates/ruff_linter/src/linter.rs
@@ -445,7 +445,7 @@ pub fn lint_only(
             &locator,
             &directives,
         ),
-        has_syntax_error: !parsed.is_valid(),
+        has_syntax_error: !parsed.is_valid() || !parsed.unsupported_syntax_errors().is_empty(),
     }
 }
 
@@ -546,7 +546,7 @@ pub fn lint_fix<'a>(
         );
 
         if iterations == 0 {
-            is_valid_syntax = parsed.is_valid();
+            is_valid_syntax = parsed.is_valid() && parsed.unsupported_syntax_errors().is_empty();
         } else {
             // If the source code was parseable on the first pass, but is no
             // longer parseable on a subsequent pass, then we've introduced a

From bd441511125c9538a99781dd0929787c066d1046 Mon Sep 17 00:00:00 2001
From: Brent Westbrook <brentrwestbrook@gmail.com>
Date: Thu, 27 Feb 2025 17:50:08 -0500
Subject: [PATCH 3/3] add `--quiet` to match snapshots in release tests

---
 crates/ruff/tests/lint.rs | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/crates/ruff/tests/lint.rs b/crates/ruff/tests/lint.rs
index 1add511de6af35..31589aa3a8ef95 100644
--- a/crates/ruff/tests/lint.rs
+++ b/crates/ruff/tests/lint.rs
@@ -2713,6 +2713,7 @@ fn cache_syntax_errors() -> Result<()> {
     cmd.args(["check", "--output-format", "concise"])
         .arg("--target-version=py39")
         .arg("--preview")
+        .arg("--quiet") // suppress `debug build without --no-cache` warnings
         .current_dir(&tempdir);
 
     assert_cmd_snapshot!(
@@ -2722,10 +2723,8 @@ fn cache_syntax_errors() -> Result<()> {
     exit_code: 1
     ----- stdout -----
     main.py:1:1: SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)
-    Found 1 error.
 
     ----- stderr -----
-    warning: Detected debug build without --no-cache.
     "
     );
 
@@ -2737,10 +2736,8 @@ fn cache_syntax_errors() -> Result<()> {
     exit_code: 1
     ----- stdout -----
     main.py:1:1: SyntaxError: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)
-    Found 1 error.
 
     ----- stderr -----
-    warning: Detected debug build without --no-cache.
     "
     );