Add InstanceMetadata builder (#269)

* Add InstanceMetadata builder, with context field for globbing

* Revert snapshot changes

* Port snapshot functions to InstanceMetadata builder-ish pattern

* Remove IgnoreGlob struct

* Elide lifetime

src/snapshot/metadata.rs

@@ -1,4 +1,7 @@
-use std::{fmt, path::PathBuf};
+use std::{
+    fmt,
+    path::{Path, PathBuf},
+};
 
 use serde::{Deserialize, Serialize};
 
@@ -42,14 +45,41 @@ pub struct InstanceMetadata {
     pub relevant_paths: Vec<PathBuf>,
 }
 
-impl Default for InstanceMetadata {
-    fn default() -> Self {
-        InstanceMetadata {
+impl InstanceMetadata {
+    pub fn new() -> Self {
+        Self {
             ignore_unknown_instances: false,
             instigating_source: None,
             relevant_paths: Vec::new(),
         }
     }
+
+    pub fn ignore_unknown_instances(self, ignore_unknown_instances: bool) -> Self {
+        Self {
+            ignore_unknown_instances,
+            ..self
+        }
+    }
+
+    pub fn instigating_source(self, instigating_source: impl Into<InstigatingSource>) -> Self {
+        Self {
+            instigating_source: Some(instigating_source.into()),
+            ..self
+        }
+    }
+
+    pub fn relevant_paths(self, relevant_paths: Vec<PathBuf>) -> Self {
+        Self {
+            relevant_paths,
+            ..self
+        }
+    }
+}
+
+impl Default for InstanceMetadata {
+    fn default() -> Self {
+        Self::new()
+    }
 }
 
 #[derive(Clone, PartialEq, Serialize, Deserialize)]
@@ -74,3 +104,9 @@ impl From<PathBuf> for InstigatingSource {
         InstigatingSource::Path(path)
     }
 }
+
+impl From<&Path> for InstigatingSource {
+    fn from(path: &Path) -> Self {
+        InstigatingSource::Path(path.to_path_buf())
+    }
+}