[red-knot] Default python-platform to current platform

crates/red_knot/src/args.rs

@@ -75,7 +75,8 @@ pub(crate) struct CheckCommand {
     ///
     /// This is used to specialize the type of `sys.platform` and will affect the visibility
     /// of platform-specific functions and attributes. If the value is set to `all`, no
-    /// assumptions are made about the target platform.
+    /// assumptions are made about the target platform. If unspecified, the current system's
+    /// platform will be used.
     #[arg(long, value_name = "PLATFORM", alias = "platform")]
     pub(crate) python_platform: Option<String>,
 

crates/red_knot_project/src/metadata/options.rs

@@ -54,20 +54,25 @@ impl Options {
         project_root: &SystemPath,
         system: &dyn System,
     ) -> ProgramSettings {
-        let (python_version, python_platform) = self
+        let python_version = self
             .environment
             .as_ref()
-            .map(|env| {
-                (
-                    env.python_version.as_deref().copied(),
-                    env.python_platform.as_deref(),
-                )
-            })
+            .and_then(|env| env.python_version.as_deref().copied())
             .unwrap_or_default();
-
+        let python_platform = self
+            .environment
+            .as_ref()
+            .and_then(|env| env.python_platform.as_deref().cloned())
+            .unwrap_or_else(|| {
+                let default = PythonPlatform::default();
+                tracing::info!(
+                    "Defaulting to default python version for this platform: '{default}'",
+                );
+                default
+            });
         ProgramSettings {
-            python_version: python_version.unwrap_or_default(),
-            python_platform: python_platform.cloned().unwrap_or_default(),
+            python_version,
+            python_platform,
             search_paths: self.to_search_path_settings(project_root, system),
         }
     }
@@ -237,7 +242,12 @@ pub struct EnvironmentOptions {
     /// If specified, Red Knot will tailor its use of type stub files,
     /// which conditionalize type definitions based on the platform.
     ///
-    /// If no platform is specified, knot will use `all` or the current platform in the LSP use case.
+    /// If no platform is specified, knot will use the current platform:
+    /// - `win32` for Windows
+    /// - `darwin` for macOS
+    /// - `android` for Android
+    /// - `ios` for iOS
+    /// - `linux` for everything else
     #[serde(skip_serializing_if = "Option::is_none")]
     pub python_platform: Option<RangedValue<PythonPlatform>>,
 

crates/red_knot_python_semantic/resources/mdtest/call/getattr_static.md

@@ -56,7 +56,7 @@ We can access attributes on objects of all kinds:
 ```py
 import sys
 
-reveal_type(inspect.getattr_static(sys, "platform"))  # revealed: LiteralString
+reveal_type(inspect.getattr_static(sys, "dont_write_bytecode"))  # revealed: bool
 reveal_type(inspect.getattr_static(inspect, "getattr_static"))  # revealed: Literal[getattr_static]
 
 reveal_type(inspect.getattr_static(1, "real"))  # revealed: property

crates/red_knot_python_semantic/resources/mdtest/sys_platform.md

@@ -1,23 +1,10 @@
 # `sys.platform`
 
-## Default value
+## Explicit selection of `all` platforms
 
-When no target platform is specified, we fall back to the type of `sys.platform` declared in
+When `python-platform="all"` is specified, we fall back to the type of `sys.platform` declared in
 typeshed:
 
-```toml
-[environment]
-# No python-platform entry
-```
-
-```py
-import sys
-
-reveal_type(sys.platform)  # revealed: LiteralString
-```
-
-## Explicit selection of `all` platforms
-
 ```toml
 [environment]
 python-platform = "all"

crates/red_knot_python_semantic/resources/mdtest/unreachable.md

@@ -195,24 +195,6 @@ if sys.platform == "win32":
     sys.getwindowsversion()
 ```
 
-##### Checking without a specified platform
-
-If `python-platform` is not specified, we currently default to `all`:
-
-```toml
-[environment]
-# python-platform not specified
-```
-
-```py
-import sys
-
-if sys.platform == "win32":
-    # TODO: we should not emit an error here
-    # error: [possibly-unbound-attribute]
-    sys.getwindowsversion()
-```
-
 ## No (incorrect) diagnostics in unreachable code
 
 ```toml

crates/red_knot_python_semantic/src/python_platform.rs

@@ -1,15 +1,14 @@
 use std::fmt::{Display, Formatter};
 
 /// The target platform to assume when resolving types.
-#[derive(Debug, Clone, Default, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 #[cfg_attr(
     feature = "serde",
     derive(serde::Serialize, serde::Deserialize),
     serde(rename_all = "kebab-case")
 )]
 pub enum PythonPlatform {
     /// Do not make any assumptions about the target platform.
-    #[default]
     All,
 
     /// Assume a specific target platform like `linux`, `darwin` or `win32`.
@@ -39,6 +38,22 @@ impl Display for PythonPlatform {
     }
 }
 
+impl Default for PythonPlatform {
+    fn default() -> Self {
+        if cfg!(target_os = "windows") {
+            PythonPlatform::Identifier("win32".to_string())
+        } else if cfg!(target_os = "macos") {
+            PythonPlatform::Identifier("darwin".to_string())
+        } else if cfg!(target_os = "android") {
+            PythonPlatform::Identifier("android".to_string())
+        } else if cfg!(target_os = "ios") {
+            PythonPlatform::Identifier("ios".to_string())
+        } else {
+            PythonPlatform::Identifier("linux".to_string())
+        }
+    }
+}
+
 #[cfg(feature = "schemars")]
 mod schema {
     use crate::PythonPlatform;

crates/red_knot_test/src/lib.rs

@@ -6,7 +6,7 @@ use config::SystemKind;
 use parser as test_parser;
 use red_knot_python_semantic::types::check_types;
 use red_knot_python_semantic::{
-    Program, ProgramSettings, PythonPath, SearchPathSettings, SysPrefixPathOrigin,
+    Program, ProgramSettings, PythonPath, PythonPlatform, SearchPathSettings, SysPrefixPathOrigin,
 };
 use ruff_db::diagnostic::{create_parse_diagnostic, Diagnostic, DisplayDiagnosticConfig};
 use ruff_db::files::{system_path_to_file, File};
@@ -265,7 +265,9 @@ fn run_test(
 
     let settings = ProgramSettings {
         python_version,
-        python_platform: configuration.python_platform().unwrap_or_default(),
+        python_platform: configuration
+            .python_platform()
+            .unwrap_or(PythonPlatform::Identifier("linux".to_string())),
         search_paths: SearchPathSettings {
             src_roots: vec![src_path],
             extra_paths: configuration.extra_paths().unwrap_or_default().to_vec(),

knot.schema.json

@@ -89,7 +89,7 @@
           ]
         },
         "python-platform": {
-          "description": "Specifies the target platform that will be used to analyze the source code. If specified, Red Knot will tailor its use of type stub files, which conditionalize type definitions based on the platform.\n\nIf no platform is specified, knot will use `all` or the current platform in the LSP use case.",
+          "description": "Specifies the target platform that will be used to analyze the source code. If specified, Red Knot will tailor its use of type stub files, which conditionalize type definitions based on the platform.\n\nIf no platform is specified, knot will use the current platform: - `win32` for Windows - `darwin` for macOS - `android` for Android - `ios` for iOS - `linux` for everything else",
           "anyOf": [
             {
               "$ref": "#/definitions/PythonPlatform"