Rename unreachable_lines to skipped_lines (#15483)

In #15164 we've made it so that `# type: ignore`s in lines skipped in
semantic analysis would not be flagged as unused.

In #15164 they were called "unreachable" lines but unreachability during
type-checking can result in the "Statement is unreachable" error, while
these statements are pruned before type-checking, so for clarity we'll
use the term "skipped".

mypy/build.py

@@ -2238,7 +2238,7 @@ def semantic_analysis_pass1(self) -> None:
         analyzer = SemanticAnalyzerPreAnalysis()
         with self.wrap_context():
             analyzer.visit_file(self.tree, self.xpath, self.id, options)
-        self.manager.errors.set_unreachable_lines(self.xpath, self.tree.unreachable_lines)
+        self.manager.errors.set_skipped_lines(self.xpath, self.tree.skipped_lines)
         # TODO: Do this while constructing the AST?
         self.tree.names = SymbolTable()
         if not self.tree.is_stub:

mypy/errors.py

@@ -223,8 +223,9 @@ class Errors:
     # (path -> line -> error-codes)
     ignored_lines: dict[str, dict[int, list[str]]]
 
-    # Lines that are statically unreachable (e.g. due to platform/version check).
-    unreachable_lines: dict[str, set[int]]
+    # Lines that were skipped during semantic analysis e.g. due to ALWAYS_FALSE, MYPY_FALSE,
+    # or platform/version checks. Those lines would not be type-checked.
+    skipped_lines: dict[str, set[int]]
 
     # Lines on which an error was actually ignored.
     used_ignored_lines: dict[str, dict[int, list[str]]]
@@ -281,7 +282,7 @@ def initialize(self) -> None:
         self.import_ctx = []
         self.function_or_member = [None]
         self.ignored_lines = {}
-        self.unreachable_lines = {}
+        self.skipped_lines = {}
         self.used_ignored_lines = defaultdict(lambda: defaultdict(list))
         self.ignored_files = set()
         self.only_once_messages = set()
@@ -330,8 +331,8 @@ def set_file_ignored_lines(
         if ignore_all:
             self.ignored_files.add(file)
 
-    def set_unreachable_lines(self, file: str, unreachable_lines: set[int]) -> None:
-        self.unreachable_lines[file] = unreachable_lines
+    def set_skipped_lines(self, file: str, skipped_lines: set[int]) -> None:
+        self.skipped_lines[file] = skipped_lines
 
     def current_target(self) -> str | None:
         """Retrieves the current target from the associated scope.
@@ -631,7 +632,7 @@ def generate_unused_ignore_errors(self, file: str) -> None:
         ignored_lines = self.ignored_lines[file]
         used_ignored_lines = self.used_ignored_lines[file]
         for line, ignored_codes in ignored_lines.items():
-            if line in self.unreachable_lines[file]:
+            if line in self.skipped_lines[file]:
                 continue
             if codes.UNUSED_IGNORE.code in ignored_codes:
                 continue

mypy/nodes.py

@@ -287,7 +287,7 @@ class MypyFile(SymbolNode):
         "names",
         "imports",
         "ignored_lines",
-        "unreachable_lines",
+        "skipped_lines",
         "is_stub",
         "is_cache_skeleton",
         "is_partial_stub_package",
@@ -314,8 +314,9 @@ class MypyFile(SymbolNode):
     # If the value is empty, ignore all errors; otherwise, the list contains all
     # error codes to ignore.
     ignored_lines: dict[int, list[str]]
-    # Lines that are statically unreachable (e.g. due to platform/version check).
-    unreachable_lines: set[int]
+    # Lines that were skipped during semantic analysis e.g. due to ALWAYS_FALSE, MYPY_FALSE,
+    # or platform/version checks. Those lines would not be type-checked.
+    skipped_lines: set[int]
     # Is this file represented by a stub file (.pyi)?
     is_stub: bool
     # Is this loaded from the cache and thus missing the actual body of the file?
@@ -348,7 +349,7 @@ def __init__(
             self.ignored_lines = ignored_lines
         else:
             self.ignored_lines = {}
-        self.unreachable_lines = set()
+        self.skipped_lines = set()
 
         self.path = ""
         self.is_stub = False

mypy/semanal_pass1.py

@@ -62,7 +62,7 @@ def visit_file(self, file: MypyFile, fnam: str, mod_id: str, options: Options) -
         self.cur_mod_node = file
         self.options = options
         self.is_global_scope = True
-        self.unreachable_lines: set[int] = set()
+        self.skipped_lines: set[int] = set()
 
         for i, defn in enumerate(file.defs):
             defn.accept(self)
@@ -74,10 +74,10 @@ def visit_file(self, file: MypyFile, fnam: str, mod_id: str, options: Options) -
                     next_def, last = file.defs[i + 1], file.defs[-1]
                     if last.end_line is not None:
                         # We are on a Python version recent enough to support end lines.
-                        self.unreachable_lines |= set(range(next_def.line, last.end_line + 1))
+                        self.skipped_lines |= set(range(next_def.line, last.end_line + 1))
                 del file.defs[i + 1 :]
                 break
-        file.unreachable_lines = self.unreachable_lines
+        file.skipped_lines = self.skipped_lines
 
     def visit_func_def(self, node: FuncDef) -> None:
         old_global_scope = self.is_global_scope
@@ -127,7 +127,7 @@ def visit_block(self, b: Block) -> None:
         if b.is_unreachable:
             if b.end_line is not None:
                 # We are on a Python version recent enough to support end lines.
-                self.unreachable_lines |= set(range(b.line, b.end_line + 1))
+                self.skipped_lines |= set(range(b.line, b.end_line + 1))
             return
         super().visit_block(b)
 

mypy/server/update.py

@@ -986,7 +986,7 @@ def key(node: FineGrainedDeferredNode) -> int:
     manager.errors.set_file_ignored_lines(
         file_node.path, file_node.ignored_lines, options.ignore_errors or state.ignore_all
     )
-    manager.errors.set_unreachable_lines(file_node.path, file_node.unreachable_lines)
+    manager.errors.set_skipped_lines(file_node.path, file_node.skipped_lines)
 
     targets = set()
     for node in nodes: