[ty] Disable possibly-missing-imports by default (#22041)

@carljm put forth a reasonably compelling argument that just disabling
this lint might be advisable. If we agree, here's the implementation.

* Fixes https://github.com/astral-sh/ty/issues/309

---------

Co-authored-by: Carl Meyer <carl@astral.sh>

.github/mypy-primer-ty.toml

@@ -4,5 +4,6 @@
 # Enable off-by-default rules.
 [rules]
 possibly-unresolved-reference = "warn"
+possibly-missing-import = "warn"
 unused-ignore-comment = "warn"
 division-by-zero = "warn"

crates/ty/docs/rules.md

@@ -2511,38 +2511,6 @@ class A:
 A()[0]  # TypeError: 'A' object is not subscriptable
 ```
 
-## `possibly-missing-import`
-
-<small>
-Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
-Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.22">0.0.1-alpha.22</a> ·
-<a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20possibly-missing-import" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1575" target="_blank">View source</a>
-</small>
-
-
-**What it does**
-
-Checks for imports of symbols that may be missing.
-
-**Why is this bad?**
-
-Importing a missing module or name will raise a `ModuleNotFoundError`
-or `ImportError` at runtime.
-
-**Examples**
-
-```python
-# module.py
-import datetime
-
-if datetime.date.today().weekday() != 6:
-    a = 1
-
-# main.py
-from module import a  # ImportError: cannot import name 'a' from 'module'
-```
-
 ## `redundant-cast`
 
 <small>
@@ -2778,6 +2746,38 @@ Dividing by zero raises a `ZeroDivisionError` at runtime.
 5 / 0
 ```
 
+## `possibly-missing-import`
+
+<small>
+Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'ignore'."><code>ignore</code></a> ·
+Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.22">0.0.1-alpha.22</a> ·
+<a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20possibly-missing-import" target="_blank">Related issues</a> ·
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1575" target="_blank">View source</a>
+</small>
+
+
+**What it does**
+
+Checks for imports of symbols that may be missing.
+
+**Why is this bad?**
+
+Importing a missing module or name will raise a `ModuleNotFoundError`
+or `ImportError` at runtime.
+
+**Examples**
+
+```python
+# module.py
+import datetime
+
+if datetime.date.today().weekday() != 6:
+    a = 1
+
+# main.py
+from module import a  # ImportError: cannot import name 'a' from 'module'
+```
+
 ## `possibly-unresolved-reference`
 
 <small>

crates/ty_python_semantic/src/types/diagnostic.rs

@@ -1594,7 +1594,7 @@ declare_lint! {
     pub(crate) static POSSIBLY_MISSING_IMPORT = {
         summary: "detects possibly missing imports",
         status: LintStatus::stable("0.0.1-alpha.22"),
-        default_level: Level::Warn,
+        default_level: Level::Ignore,
     }
 }
 

crates/ty_server/tests/e2e/snapshots/e2e__commands__debug_command.snap

@@ -89,7 +89,6 @@ Settings: Settings {
         "positional-only-parameter-as-kwarg": Error (Default),
         "possibly-missing-attribute": Warning (Default),
         "possibly-missing-implicit-call": Warning (Default),
-        "possibly-missing-import": Warning (Default),
         "raw-string-type-annotation": Error (Default),
         "redundant-cast": Warning (Default),
         "static-assert-error": Error (Default),

ty.schema.json

@@ -926,7 +926,7 @@
         "possibly-missing-import": {
           "title": "detects possibly missing imports",
           "description": "## What it does\nChecks for imports of symbols that may be missing.\n\n## Why is this bad?\nImporting a missing module or name will raise a `ModuleNotFoundError`\nor `ImportError` at runtime.\n\n## Examples\n```python\n# module.py\nimport datetime\n\nif datetime.date.today().weekday() != 6:\n    a = 1\n\n# main.py\nfrom module import a  # ImportError: cannot import name 'a' from 'module'\n```",
-          "default": "warn",
+          "default": "ignore",
           "oneOf": [
             {
               "$ref": "#/definitions/Level"