Enable new semantic analyzer by default (#7174)

The old semantic analyzer is still there and can be used with `--no-new-semantic-analyzer`. For running tests one can use `NEWSEMANAL=0`.

.travis.yml

@@ -22,19 +22,19 @@ jobs:
     python: 3.6    # 3.6.3  pip  9.0.1
   - name: "run test suite with python 3.7"
     python: 3.7    # 3.7.0  pip 10.0.1
-  - name: "run test suite with python 3.5.1 (new semantic analyzer)"
+  - name: "run test suite with python 3.5.1 (old semantic analyzer)"
     python: 3.5.1
     dist: trusty
     env:
     - TOXENV=py
     - EXTRA_ARGS="-n 12"
-    - NEWSEMANAL=1
-  - name: "run test suite with python 3.7 (new semantic analyzer)"
+    - NEWSEMANAL=0
+  - name: "run test suite with python 3.7 (old semantic analyzer)"
     python: 3.7
     env:
     - TOXENV=py
     - EXTRA_ARGS="-n 12"
-    - NEWSEMANAL=1
+    - NEWSEMANAL=0
   - name: "run test suite with python 3.7 (compiled with mypyc)"
     python: 3.7
     env:

docs/source/command_line.rst

@@ -659,18 +659,17 @@ Miscellaneous
     have many scripts that import a large package, the behavior enabled
     by this flag is often more convenient.)
 
-``--new-semantic-analyzer``
-    This flag switches to an improved, experimental implementation of
+``--no-new-semantic-analyzer``
+    This flag disables the improved implementation of
     the *semantic analyzer* (the part of mypy that binds Python
     names to definitions). The old and the new semantic analyzers
     mostly behave identically. The new semantic analyzer is better at
     handling import cycles and forward references to definitions. It
     also fixes inconsistencies between the daemon and non-daemon modes,
     and it detects additional error conditions.
 
-    Likely, the next mypy release will use the new semantic analyzer by
-    default, and the old semantic analyzer will be removed in the next
-    release after that.
+    Likely, the old semantic analyzer will be removed in the next
+    release.
 
 .. _PEP 420: https://www.python.org/dev/peps/pep-0420/
 

docs/source/config_file.rst

@@ -470,6 +470,6 @@ Miscellaneous
 ``verbosity`` (integer, default 0)
     Controls how much debug output will be generated.  Higher numbers are more verbose.
 
-``new_semantic_analyzer`` (bool, default False)
-    Enables the experimental new semantic analyzer.
+``new_semantic_analyzer`` (bool, default True)
+    Enables the new, improved, semantic analyzer.
     (See :ref:`The mypy command line <command-line>` for more information.)

mypy/main.py

@@ -554,7 +554,8 @@ def add_invertible_flag(flag: str,
              "the contents of SHADOW_FILE instead.")
     add_invertible_flag('--fast-exit', default=False, help=argparse.SUPPRESS,
                         group=internals_group)
-    add_invertible_flag('--new-semantic-analyzer', default=False, help=argparse.SUPPRESS,
+    add_invertible_flag('--no-new-semantic-analyzer', dest='new_semantic_analyzer',
+                        default=True, help=argparse.SUPPRESS,
                         group=internals_group)
 
     error_group = parser.add_argument_group(

mypy/options.py

@@ -87,7 +87,12 @@ def __init__(self) -> None:
         self.namespace_packages = False
 
         # Use the new semantic analyzer
-        self.new_semantic_analyzer = bool(os.getenv('NEWSEMANAL'))
+        new_analyzer = os.getenv('NEWSEMANAL')
+        if new_analyzer:
+            # Use NEWSEMANAL=0 to change the default (for tests).
+            self.new_semantic_analyzer = bool(int(new_analyzer))
+        else:
+            self.new_semantic_analyzer = True
 
         # disallow_any options
         self.disallow_any_generics = False