Port commands to use common setup code

Initialization logic needed for serve, build, and upload is now
much more clear than it was when these functions were written.

This commit refactors all of them to use a new common_setup
module for all of their initialization that's the same.

src/common_setup.rs

@@ -0,0 +1,66 @@
+//! Initialization routines that are used by more than one Rojo command or
+//! utility.
+
+use std::path::Path;
+
+use rbx_dom_weak::RbxInstanceProperties;
+
+use crate::{
+    imfs::{Imfs, ImfsFetcher},
+    project::{Project, ProjectLoadError},
+    snapshot::{apply_patch_set, compute_patch_set, InstancePropertiesWithMeta, RojoTree},
+    snapshot_middleware::{snapshot_from_imfs, InstanceSnapshotContext, SnapshotPluginContext},
+};
+
+pub fn start<F: ImfsFetcher>(
+    fuzzy_project_path: &Path,
+    imfs: &mut Imfs<F>,
+) -> (Option<Project>, RojoTree) {
+    log::trace!("Loading project file from {}", fuzzy_project_path.display());
+    let maybe_project = match Project::load_fuzzy(fuzzy_project_path) {
+        Ok(project) => Some(project),
+        Err(ProjectLoadError::NotFound) => None,
+        Err(other) => panic!("{}", other), // TODO: return error upward
+    };
+
+    log::trace!("Constructing initial tree");
+    let mut tree = RojoTree::new(InstancePropertiesWithMeta {
+        properties: RbxInstanceProperties {
+            name: "ROOT".to_owned(),
+            class_name: "Folder".to_owned(),
+            properties: Default::default(),
+        },
+        metadata: Default::default(),
+    });
+
+    let root_id = tree.get_root_id();
+
+    log::trace!("Constructing snapshot context");
+    let mut snapshot_context = InstanceSnapshotContext::default();
+    if let Some(project) = &maybe_project {
+        // If the project file defines no plugins, then there's no need to
+        // initialize the snapshot plugin context.
+        if !project.plugins.is_empty() {
+            snapshot_context.plugin_context =
+                Some(SnapshotPluginContext::new(project.plugins.clone()));
+        }
+    }
+
+    log::trace!("Reading project root");
+    let entry = imfs
+        .get(fuzzy_project_path)
+        .expect("could not get project path");
+
+    log::trace!("Generating snapshot of instances from IMFS");
+    let snapshot = snapshot_from_imfs(&mut snapshot_context, imfs, &entry)
+        .expect("snapshot failed")
+        .expect("snapshot did not return an instance");
+
+    log::trace!("Computing patch set");
+    let patch_set = compute_patch_set(&snapshot, &tree, root_id);
+
+    log::trace!("Applying patch set");
+    apply_patch_set(&mut tree, patch_set);
+
+    (maybe_project, tree)
+}