Break redaction stuff out into separate crate

rojo-insta-ext/Cargo.toml

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+[package]
+name = "rojo-insta-ext"
+version = "0.1.0"
+authors = ["Lucien Greathouse <me@lpghatguy.com>"]
+edition = "2018"
+publish = false
+
+[dependencies]
+serde = "1.0.99"
+serde_yaml = "0.8.9"
+
+[dependencies.insta]
+version = "0.11.0"
+features = ["redactions"]

rojo-insta-ext/README.md

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+# Rojo Insta Extensions
+This crate has add-ons intended for use with Insta that are useful for snapshot tests.

rojo-insta-ext/src/lib.rs

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+mod redaction_map;
+
+pub use redaction_map::*;

rojo-insta-ext/src/redaction_map.rs

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+use std::collections::HashMap;
+
+use serde::Serialize;
+
+/// Enables redacting any value that serializes as a string.
+///
+/// Used for transforming Rojo instance IDs into something deterministic.
+pub struct RedactionMap {
+    ids: HashMap<String, usize>,
+    last_id: usize,
+}
+
+impl RedactionMap {
+    pub fn new() -> Self {
+        Self {
+            ids: HashMap::new(),
+            last_id: 0,
+        }
+    }
+
+    pub fn intern(&mut self, id: impl ToString) {
+        let last_id = &mut self.last_id;
+
+        self.ids.entry(id.to_string()).or_insert_with(|| {
+            *last_id += 1;
+            *last_id
+        });
+    }
+
+    pub fn intern_iter<S: ToString>(&mut self, ids: impl Iterator<Item = S>) {
+        for id in ids {
+            self.intern(id.to_string());
+        }
+    }
+
+    pub fn redacted_yaml(&self, value: impl Serialize) -> serde_yaml::Value {
+        let mut encoded = serde_yaml::to_value(value).expect("Couldn't encode value as YAML");
+
+        self.redact(&mut encoded);
+        encoded
+    }
+
+    pub fn redact(&self, yaml_value: &mut serde_yaml::Value) {
+        use serde_yaml::{Mapping, Value};
+
+        match yaml_value {
+            Value::String(value) => {
+                if let Some(redacted) = self.ids.get(value) {
+                    *yaml_value = Value::String(format!("id-{}", *redacted));
+                }
+            }
+            Value::Sequence(sequence) => {
+                for value in sequence {
+                    self.redact(value);
+                }
+            }
+            Value::Mapping(mapping) => {
+                // We can't mutate the keys of a map in-place, so we take
+                // ownership of the map and rebuild it.
+
+                let owned_map = std::mem::replace(mapping, Mapping::new());
+                let mut new_map = Mapping::with_capacity(owned_map.len());
+
+                for (mut key, mut value) in owned_map {
+                    self.redact(&mut key);
+                    self.redact(&mut value);
+                    new_map.insert(key, value);
+                }
+
+                *mapping = new_map;
+            }
+            _ => {}
+        }
+    }
+}