Add unreachable code rule (#5384)

Co-authored-by: Thomas de Zeeuw <[email protected]>
Co-authored-by: Micha Reiser <[email protected]>

.gitattributes

@@ -4,3 +4,4 @@ crates/ruff/resources/test/fixtures/isort/line_ending_crlf.py text eol=crlf
 crates/ruff/resources/test/fixtures/pycodestyle/W605_1.py text eol=crlf
 
 ruff.schema.json linguist-generated=true text=auto eol=lf
+*.md.snap linguist-language=Markdown

crates/ruff/Cargo.toml

@@ -17,6 +17,7 @@ name = "ruff"
 [dependencies]
 ruff_cache = { path = "../ruff_cache" }
 ruff_diagnostics = { path = "../ruff_diagnostics", features = ["serde"] }
+ruff_index = { path = "../ruff_index" }
 ruff_macros = { path = "../ruff_macros" }
 ruff_python_whitespace = { path = "../ruff_python_whitespace" }
 ruff_python_ast = { path = "../ruff_python_ast", features = ["serde"] }
@@ -88,3 +89,5 @@ colored = { workspace = true, features = ["no-color"] }
 [features]
 default = []
 schemars = ["dep:schemars"]
+# Enables the UnreachableCode rule
+unreachable-code = []

crates/ruff/resources/test/fixtures/control-flow-graph/assert.py

@@ -0,0 +1,11 @@
+def func():
+    assert True
+
+def func():
+    assert False
+
+def func():
+    assert True, "oops"
+
+def func():
+    assert False, "oops"

crates/ruff/resources/test/fixtures/control-flow-graph/async-for.py

@@ -0,0 +1,41 @@
+def func():
+    async for i in range(5):
+        print(i)
+
+def func():
+    async for i in range(20):
+        print(i)
+    else:
+        return 0
+
+def func():
+    async for i in range(10):
+        if i == 5:
+            return 1
+    return 0
+
+def func():
+    async for i in range(111):
+        if i == 5:
+            return 1
+    else:
+        return 0
+    return 2
+
+def func():
+    async for i in range(12):
+        continue
+
+def func():
+    async for i in range(1110):
+        if True:
+            continue
+
+def func():
+    async for i in range(13):
+        break
+
+def func():
+    async for i in range(1110):
+        if True:
+            break

crates/ruff/resources/test/fixtures/control-flow-graph/for.py

@@ -0,0 +1,41 @@
+def func():
+    for i in range(5):
+        print(i)
+
+def func():
+    for i in range(20):
+        print(i)
+    else:
+        return 0
+
+def func():
+    for i in range(10):
+        if i == 5:
+            return 1
+    return 0
+
+def func():
+    for i in range(111):
+        if i == 5:
+            return 1
+    else:
+        return 0
+    return 2
+
+def func():
+    for i in range(12):
+        continue
+
+def func():
+    for i in range(1110):
+        if True:
+            continue
+
+def func():
+    for i in range(13):
+        break
+
+def func():
+    for i in range(1110):
+        if True:
+            break

crates/ruff/resources/test/fixtures/control-flow-graph/if.py

@@ -0,0 +1,108 @@
+def func():
+    if False:
+        return 0
+    return 1
+
+def func():
+    if True:
+        return 1
+    return 0
+
+def func():
+    if False:
+        return 0
+    else:
+        return 1
+
+def func():
+    if True:
+        return 1
+    else:
+        return 0
+
+def func():
+    if False:
+        return 0
+    else:
+        return 1
+    return "unreachable"
+
+def func():
+    if True:
+        return 1
+    else:
+        return 0
+    return "unreachable"
+
+def func():
+    if True:
+        if True:
+            return 1
+        return 2
+    else:
+        return 3
+    return "unreachable2"
+
+def func():
+    if False:
+        return 0
+
+def func():
+    if True:
+        return 1
+
+def func():
+    if True:
+        return 1
+    elif False:
+        return 2
+    else:
+        return 0
+
+def func():
+    if False:
+        return 1
+    elif True:
+        return 2
+    else:
+        return 0
+
+def func():
+    if True:
+        if False:
+            return 0
+        elif True:
+            return 1
+        else:
+            return 2
+        return 3
+    elif True:
+        return 4
+    else:
+        return 5
+    return 6
+
+def func():
+    if False:
+        return "unreached"
+    elif False:
+        return "also unreached"
+    return "reached"
+
+# Test case found in the Bokeh repository that trigger a false positive.
+def func(self, obj: BytesRep) -> bytes:
+    data = obj["data"]
+
+    if isinstance(data, str):
+        return base64.b64decode(data)
+    elif isinstance(data, Buffer):
+        buffer = data
+    else:
+        id = data["id"]
+
+        if id in self._buffers:
+            buffer = self._buffers[id]
+        else:
+            self.error(f"can't resolve buffer '{id}'")
+
+    return buffer.data

crates/ruff/resources/test/fixtures/control-flow-graph/match.py

@@ -0,0 +1,131 @@
+def func(status):
+    match status:
+        case _:
+            return 0
+    return "unreachable"
+
+def func(status):
+    match status:
+        case 1:
+            return 1
+    return 0
+
+def func(status):
+    match status:
+        case 1:
+            return 1
+        case _:
+            return 0
+
+def func(status):
+    match status:
+        case 1 | 2 | 3:
+            return 5
+    return 6
+
+def func(status):
+    match status:
+        case 1 | 2 | 3:
+            return 5
+        case _:
+            return 10
+    return 0
+
+def func(status):
+    match status:
+        case 0:
+            return 0
+        case 1:
+            return 1
+        case 1:
+            return "1 again"
+        case _:
+            return 3
+
+def func(status):
+    i = 0
+    match status, i:
+        case _, _:
+            return 0
+
+def func(status):
+    i = 0
+    match status, i:
+        case _, 0:
+            return 0
+        case _, 2:
+            return 0
+
+def func(point):
+    match point:
+        case (0, 0):
+            print("Origin")
+        case _:
+            raise ValueError("oops")
+
+def func(point):
+    match point:
+        case (0, 0):
+            print("Origin")
+        case (0, y):
+            print(f"Y={y}")
+        case (x, 0):
+            print(f"X={x}")
+        case (x, y):
+            print(f"X={x}, Y={y}")
+        case _:
+            raise ValueError("Not a point")
+
+def where_is(point):
+    class Point:
+        x: int
+        y: int
+
+    match point:
+        case Point(x=0, y=0):
+            print("Origin")
+        case Point(x=0, y=y):
+            print(f"Y={y}")
+        case Point(x=x, y=0):
+            print(f"X={x}")
+        case Point():
+            print("Somewhere else")
+        case _:
+            print("Not a point")
+
+def func(points):
+    match points:
+        case []:
+            print("No points")
+        case [Point(0, 0)]:
+            print("The origin")
+        case [Point(x, y)]:
+            print(f"Single point {x}, {y}")
+        case [Point(0, y1), Point(0, y2)]:
+            print(f"Two on the Y axis at {y1}, {y2}")
+        case _:
+            print("Something else")
+
+def func(point):
+    match point:
+        case Point(x, y) if x == y:
+            print(f"Y=X at {x}")
+        case Point(x, y):
+            print(f"Not on the diagonal")
+
+def func():
+    from enum import Enum
+    class Color(Enum):
+        RED = 'red'
+        GREEN = 'green'
+        BLUE = 'blue'
+
+    color = Color(input("Enter your choice of 'red', 'blue' or 'green': "))
+
+    match color:
+        case Color.RED:
+            print("I see red!")
+        case Color.GREEN:
+            print("Grass is green")
+        case Color.BLUE:
+            print("I'm feeling the blues :(")

crates/ruff/resources/test/fixtures/control-flow-graph/raise.py

@@ -0,0 +1,5 @@
+def func():
+    raise Exception
+
+def func():
+    raise "a glass!"

crates/ruff/resources/test/fixtures/control-flow-graph/simple.py

@@ -0,0 +1,23 @@
+def func():
+    pass
+
+def func():
+    pass
+
+def func():
+    return
+
+def func():
+    return 1
+
+def func():
+    return 1
+    return "unreachable"
+
+def func():
+    i = 0
+
+def func():
+    i = 0
+    i += 2
+    return i