Fix match statement issue

.gitignore

@@ -125,4 +125,10 @@ junit.xml
 Thumbs.db
 
 # Potential venv
-.venv
+.venv
+
+# Agent files
+serena/
+.beads/
+AGENTS.md
+

packages/pyright-internal/src/analyzer/patternMatching.ts

@@ -1423,6 +1423,12 @@ function getSequencePatternInfo(
                     // If the tuple contains an indeterminate entry, expand or remove that
                     // entry to match the length of the pattern if possible.
                     let expandedIndeterminate = false;
+                    // Track when we remove an unbounded entry. When removedIndeterminate is true,
+                    // tupleIndeterminateIndex becomes -1, making isUnboundedTuple false in the
+                    // sequenceInfo entry. This is safe because isPotentialNoMatch=true (set below)
+                    // prevents incorrect elimination at the isDefiniteMatch check before the
+                    // isIndeterminateLength || isUnboundedTuple guard matters.
+                    let removedIndeterminate = false;
                     if (tupleIndeterminateIndex >= 0) {
                         tupleDeterminateEntryCount--;
 
@@ -1435,6 +1441,7 @@ function getSequencePatternInfo(
 
                         if (typeArgs.length > patternEntryCount && patternStarEntryIndex === undefined) {
                             typeArgs.splice(tupleIndeterminateIndex, 1);
+                            removedIndeterminate = true;
                             tupleIndeterminateIndex = -1;
                         }
                     }
@@ -1474,6 +1481,13 @@ function getSequencePatternInfo(
                         let isDefiniteNoMatch = false;
                         let isPotentialNoMatch = tupleIndeterminateIndex >= 0;
 
+                        // If we removed an unbounded entry to make the lengths match,
+                        // this is a potential match (not definite) because the original
+                        // tuple could have different lengths.
+                        if (removedIndeterminate) {
+                            isPotentialNoMatch = true;
+                        }
+
                         // If the pattern includes a "star entry" and the tuple includes an
                         // indeterminate-length entry that aligns to the star entry, we can
                         // assume it will always match.

packages/pyright-internal/src/tests/samples/matchSequenceVariadic.py

@@ -0,0 +1,34 @@
+# This sample tests pattern matching with variadic tuple types.
+# From the regression report for Pyright 1.1.408.
+
+from typing import TypeAlias, assert_type
+
+Func6Input: TypeAlias = tuple[int] | tuple[str, str] | tuple[int, *tuple[str, ...], int]
+
+
+def func6(val: Func6Input):
+    match val:
+        case (x,):
+            # Type may be narrowed to tuple[int].
+            # E: Argument of type "tuple[int]" cannot be assigned to parameter of type "tuple[int] | tuple[str, str] | tuple[int, *tuple[str, ...], int]"
+            assert_type(val, Func6Input)
+            assert_type(val, tuple[int])
+
+        case (x, y):
+            # Type may be narrowed to tuple[str, str] | tuple[int, int].
+            # E: Argument of type "tuple[str, str] | tuple[int, int]" cannot be assigned to parameter of type "tuple[int] | tuple[str, str] | tuple[int, *tuple[str, ...], int]"
+            assert_type(val, Func6Input)
+            assert_type(val, tuple[str, str] | tuple[int, int])
+
+        case (x, y, z):
+            # Type may be narrowed to tuple[int, str, int].
+            # This case should be reachable!
+            # E: Argument of type "tuple[int, str, int]" cannot be assigned to parameter of type "tuple[int] | tuple[str, str] | tuple[int, *tuple[str, ...], int]"
+            assert_type(val, Func6Input)
+            assert_type(val, tuple[int, str, int])
+
+        case (w, x, y, z):
+            # Type may be narrowed to tuple[int, str, str, int].
+            # E: Argument of type "tuple[int, str, str, int]" cannot be assigned to parameter of type "tuple[int] | tuple[str, str] | tuple[int, *tuple[str, ...], int]"
+            assert_type(val, Func6Input)
+            assert_type(val, tuple[int, str, str, int])

packages/pyright-internal/src/tests/typeEvaluator6.test.ts

@@ -471,6 +471,15 @@ test('MatchSequence2', () => {
     TestUtils.validateResults(analysisResults, 0);
 });
 
+test('MatchSequenceVariadic', () => {
+    const configOptions = new ConfigOptions(Uri.empty());
+
+    configOptions.defaultPythonVersion = pythonVersion3_12;
+    const analysisResults = TestUtils.typeAnalyzeSampleFiles(['matchSequenceVariadic.py'], configOptions);
+    // After fix: should be 4 errors and 0 unreachable code
+    TestUtils.validateResults(analysisResults, 4, 0, undefined, undefined, 0);
+});
+
 test('MatchClass1', () => {
     const configOptions = new ConfigOptions(Uri.empty());