Add do_migrate_from_v0() implementation

cargo-dist/src/errors.rs

@@ -74,6 +74,10 @@ pub enum DistError {
     #[error(transparent)]
     TripleError(#[from] dist_schema::target_lexicon::ParseError),
 
+    /// error when using axoasset::toml::to_string() or similar
+    #[error(transparent)]
+    AxoassetTomlSerErr(#[from] axoasset::toml::ser::Error),
+
     /// A problem with a jinja template, which is always a dist bug
     #[error("Failed to render template")]
     #[diagnostic(

cargo-dist/src/migrate/from_v0.rs

@@ -1,5 +1,50 @@
-use crate::errors::DistResult;
+use crate::{config, errors::DistResult};
+use crate::config::v0::V0DistConfig;
+use crate::config::v1::DistConfig;
+use axoasset::toml;
+
+// A purely-functional subset of `do_migrate_from_v0()`:
+// takes a DistMetadata (v0) and returns an equivalent DistConfig (v1)
+// without touching files on disk.
+//
+// This could theoretically have unit tests written for it, but we would
+// need to make every piece of DistConfig derive/impl PartialEq, which is
+// a lot. -duckinator
+fn migrate_from_v0_dist_config(old_config: V0DistConfig) -> DistConfig {
+    let dist = old_config.dist.map(|dist| dist.to_toml_layer(true));
+    let workspace = old_config.workspace;
+    let package = old_config.package;
+
+    config::v1::DistConfig {
+        dist,
+        workspace,
+        package,
+    }
+}
 
 pub fn do_migrate_from_v0() -> DistResult<()> {
-    unimplemented!()
+    let workspaces = config::get_project()?;
+    let root_workspace = workspaces.root_workspace();
+    let manifest_path = &root_workspace.manifest_path;
+
+    if config::v1::load(manifest_path).is_ok() {
+        // We're already on a V1 config, no need to migrate!
+        return Ok(());
+    }
+
+    // Load in the root workspace toml to edit and write back
+    let Ok(old_config) = config::v0::load(manifest_path) else {
+        // We don't have a valid v0 _or_ v1 config. No migration can be done.
+        // It feels weird to return Ok(()) here, but I think it's right?
+        return Ok(());
+    };
+
+    let config = migrate_from_v0_dist_config(old_config);
+
+    let workspace_toml_text = toml::to_string(&config)?;
+
+    // Write new config file.
+    axoasset::LocalAsset::write_new(&workspace_toml_text, manifest_path)?;
+
+    Ok(())
 }