feat(init): add default-platforms config support

crates/pixi_cli/src/init.rs

@@ -299,7 +299,12 @@ pub async fn execute(args: Args) -> miette::Result<()> {
     let version = "0.1.0";
     let author = get_default_author();
     let platforms = if args.platforms.is_empty() {
-        vec![Platform::current().to_string()]
+        let config_platforms = config.default_platforms();
+        if config_platforms.is_empty() {
+            vec![Platform::current().to_string()]
+        } else {
+            config_platforms
+        }
     } else {
         args.platforms.clone()
     };
@@ -744,4 +749,72 @@ mod tests {
             );
         }
     }
+
+    #[tokio::test]
+    async fn test_default_platforms_usage() {
+        use pixi_config::Config;
+        use tempfile::tempdir;
+
+        let temp_dir = tempdir().unwrap();
+        let config_dir = temp_dir.path().join(".pixi");
+        fs_err::create_dir_all(&config_dir).unwrap();
+        let config_file = config_dir.join("config.toml");
+
+        // Create a config with default platforms
+        let config_content = r#"default-platforms = ["win-64", "linux-64", "osx-64"]"#;
+        fs_err::write(&config_file, config_content).unwrap();
+
+        // Parse the config
+        let (config, _) = Config::from_toml(config_content, Some(&config_file)).unwrap();
+
+        // Test that default_platforms() returns the expected values
+        assert_eq!(
+            config.default_platforms(),
+            vec!["win-64", "linux-64", "osx-64"]
+        );
+
+        // Test init args with empty platforms should use config defaults
+        let args = Args {
+            path: temp_dir.path().to_path_buf(),
+            channels: None,
+            platforms: vec![], // Empty platforms
+            env_file: None,
+            format: None,
+            pyproject_toml: false,
+            scm: None,
+        };
+
+        // Test the platform selection logic matches what's in execute()
+        let platforms = if args.platforms.is_empty() {
+            let config_platforms = config.default_platforms();
+            if config_platforms.is_empty() {
+                vec![Platform::current().to_string()]
+            } else {
+                config_platforms
+            }
+        } else {
+            args.platforms.clone()
+        };
+
+        assert_eq!(platforms, vec!["win-64", "linux-64", "osx-64"]);
+
+        // Test with explicit platforms should override config
+        let args_with_platforms = Args {
+            platforms: vec!["linux-aarch64".to_string()],
+            ..args
+        };
+
+        let platforms_override = if args_with_platforms.platforms.is_empty() {
+            let config_platforms = config.default_platforms();
+            if config_platforms.is_empty() {
+                vec![Platform::current().to_string()]
+            } else {
+                config_platforms
+            }
+        } else {
+            args_with_platforms.platforms.clone()
+        };
+
+        assert_eq!(platforms_override, vec!["linux-aarch64"]);
+    }
 }

crates/pixi_config/src/lib.rs

@@ -628,6 +628,11 @@ pub struct Config {
     #[serde(skip_serializing_if = "Vec::is_empty")]
     pub default_channels: Vec<NamedChannelOrUrl>,
 
+    #[serde(default)]
+    #[serde(alias = "default_platforms")] // BREAK: remove to stop supporting snake_case alias
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    pub default_platforms: Vec<String>,
+
     /// Path to the file containing the authentication token.
     #[serde(default)]
     #[serde(alias = "authentication_override_file")] // BREAK: remove to stop supporting snake_case alias
@@ -736,6 +741,7 @@ impl Default for Config {
     fn default() -> Self {
         Self {
             default_channels: Vec::new(),
+            default_platforms: Vec::new(),
             authentication_override_file: None,
             tls_no_verify: None,
             mirrors: HashMap::new(),
@@ -1339,6 +1345,11 @@ impl Config {
             } else {
                 other.default_channels
             },
+            default_platforms: if other.default_platforms.is_empty() {
+                self.default_platforms
+            } else {
+                other.default_platforms
+            },
             tls_no_verify: other.tls_no_verify.or(self.tls_no_verify),
             authentication_override_file: other
                 .authentication_override_file
@@ -1384,6 +1395,11 @@ impl Config {
         }
     }
 
+    /// Retrieve the value for the default_platforms field (defaults to empty).
+    pub fn default_platforms(&self) -> Vec<String> {
+        self.default_platforms.clone()
+    }
+
     /// Retrieve the value for the tls_no_verify field (defaults to false).
     pub fn tls_no_verify(&self) -> bool {
         self.tls_no_verify.unwrap_or(false)
@@ -2102,6 +2118,7 @@ UNUSED = "unused"
         let mut config = Config::default();
         let other = Config {
             default_channels: vec![NamedChannelOrUrl::from_str("conda-forge").unwrap()],
+            default_platforms: vec!["linux-64".to_string()],
             channel_config: ChannelConfig::default_with_root_dir(PathBuf::from("/root/dir")),
             tls_no_verify: Some(true),
             detached_environments: Some(DetachedEnvironments::Path(PathBuf::from("/path/to/envs"))),
@@ -2854,4 +2871,78 @@ UNUSED = "unused"
             }
         );
     }
+
+    #[test]
+    fn test_config_parse_default_platforms() {
+        // Test parsing default_platforms from TOML
+        let toml = r#"default-platforms = ["win-64", "linux-64", "osx-64"]"#;
+        let (config, _) = Config::from_toml(toml, None).unwrap();
+        assert_eq!(
+            config.default_platforms,
+            vec!["win-64", "linux-64", "osx-64"]
+        );
+        assert_eq!(
+            config.default_platforms(),
+            vec!["win-64", "linux-64", "osx-64"]
+        );
+
+        // Test empty default_platforms (should return empty vec)
+        let toml = r#"default-platforms = []"#;
+        let (config, _) = Config::from_toml(toml, None).unwrap();
+        assert_eq!(config.default_platforms, Vec::<String>::new());
+        assert_eq!(config.default_platforms(), Vec::<String>::new());
+
+        // Test missing default_platforms (should default to empty)
+        let toml = r#"tls-no-verify = true"#;
+        let (config, _) = Config::from_toml(toml, None).unwrap();
+        assert_eq!(config.default_platforms, Vec::<String>::new());
+        assert_eq!(config.default_platforms(), Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_config_merge_default_platforms() {
+        // Test that higher priority config overrides lower priority for default_platforms
+        let base_config = Config {
+            default_platforms: vec!["linux-64".to_string()],
+            ..Config::default()
+        };
+
+        let override_config = Config {
+            default_platforms: vec!["win-64".to_string(), "osx-64".to_string()],
+            ..Config::default()
+        };
+
+        let merged = base_config.merge_config(override_config);
+        assert_eq!(merged.default_platforms, vec!["win-64", "osx-64"]);
+
+        // Test that empty override doesn't change base
+        let base_config = Config {
+            default_platforms: vec!["linux-64".to_string()],
+            ..Config::default()
+        };
+
+        let empty_override = Config::default();
+
+        let merged = base_config.merge_config(empty_override);
+        assert_eq!(merged.default_platforms, vec!["linux-64"]);
+    }
+
+    #[test]
+    fn test_config_parse_combined_defaults() {
+        // Test that both default_channels and default_platforms work together
+        let toml = r#"
+default-channels = ["conda-forge", "bioconda"]
+default-platforms = ["win-64", "linux-64"]
+"#;
+        let (config, _) = Config::from_toml(toml, None).unwrap();
+
+        assert_eq!(
+            config.default_channels,
+            vec![
+                NamedChannelOrUrl::from_str("conda-forge").unwrap(),
+                NamedChannelOrUrl::from_str("bioconda").unwrap()
+            ]
+        );
+        assert_eq!(config.default_platforms, vec!["win-64", "linux-64"]);
+    }
 }

crates/pixi_config/src/snapshots/pixi_config__tests__config_merge_multiple.snap

@@ -14,6 +14,7 @@ Config {
             "defaults",
         ),
     ],
+    default_platforms: [],
     authentication_override_file: None,
     tls_no_verify: Some(
         false,

docs/reference/pixi_configuration.md

@@ -56,6 +56,7 @@ For backwards compatibility, the following configuration options can still be wr
 in `snake_case`:
 
     - `default_channels`
+    - `default_platforms`
     - `change_ps1`
     - `tls_no_verify`
     - `authentication_override_file`
@@ -77,6 +78,18 @@ This defaults to only conda-forge.
 The `default-channels` are only used when initializing a new project. Once initialized the `channels` are used from the
 project manifest.
 
+### `default-platforms`
+
+The default platforms to select when running `pixi init`.
+This defaults to the current platform if not specified.
+
+```toml title="config.toml"
+default-platforms = ["win-64", "linux-64", "osx-64"]
+```
+
+!!! note
+The `default-platforms` are only used when initializing a new project. You can override this by explicitly providing platforms with the `--platform` flag.
+
 ### `shell`
 
 - `change-ps1`:  When set to `false`, the `(pixi)` prefix in the shell prompt is removed.