diff --git a/Cargo.lock b/Cargo.lock
index 01269091dd4..56dbf7ba890 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -468,9 +468,9 @@ checksum = "6184e33543162437515c2e2b48714794e37845ec9851711914eec9d308f6ebe8"
 
 [[package]]
 name = "digest"
-version = "0.10.3"
+version = "0.10.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f2fb860ca6fafa5552fb6d0e816a69c8e49f0908bf524e30a90d97c85892d506"
+checksum = "adfbc57365a37acbd2ebf2b64d7e69bb766e2fea813521ed536f5d0520dcf86c"
 dependencies = [
  "block-buffer",
  "crypto-common",
@@ -754,6 +754,7 @@ dependencies = [
  "bytes",
  "chrono",
  "config",
+ "digest",
  "git2",
  "hex",
  "insta",
diff --git a/lib/Cargo.toml b/lib/Cargo.toml
index 5e3365b142e..026ac561fcc 100644
--- a/lib/Cargo.toml
+++ b/lib/Cargo.toml
@@ -24,6 +24,7 @@ bytes = "1.2.1"
 byteorder = "1.4.3"
 chrono = { version = "0.4.22", default-features = false, features = ["std", "clock"] }
 config = { version = "0.13.2", default-features = false, features = ["toml"] }
+digest = "0.10.5"
 git2 = "0.15.0"
 hex = "0.4.3"
 itertools = "0.10.5"
diff --git a/lib/src/backend.rs b/lib/src/backend.rs
index 08cd46fbed6..b3a323adadd 100644
--- a/lib/src/backend.rs
+++ b/lib/src/backend.rs
@@ -22,8 +22,10 @@ use thiserror::Error;
 
 use crate::repo_path::{RepoPath, RepoPathComponent};
 
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
-pub struct CommitId(Vec<u8>);
+content_hash! {
+    #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
+    pub struct CommitId(Vec<u8>);
+}
 
 impl Debug for CommitId {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
@@ -225,14 +227,18 @@ pub enum Phase {
     Draft,
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, PartialOrd, Ord)]
-pub struct MillisSinceEpoch(pub i64);
+content_hash! {
+    #[derive(Debug, PartialEq, Eq, Clone, PartialOrd, Ord)]
+    pub struct MillisSinceEpoch(pub i64);
+}
 
-#[derive(Debug, PartialEq, Eq, Clone, PartialOrd, Ord)]
-pub struct Timestamp {
-    pub timestamp: MillisSinceEpoch,
-    // time zone offset in minutes
-    pub tz_offset: i32,
+content_hash! {
+    #[derive(Debug, PartialEq, Eq, Clone, PartialOrd, Ord)]
+    pub struct Timestamp {
+        pub timestamp: MillisSinceEpoch,
+        // time zone offset in minutes
+        pub tz_offset: i32,
+    }
 }
 
 impl Timestamp {
diff --git a/lib/src/content_hash.rs b/lib/src/content_hash.rs
new file mode 100644
index 00000000000..4a79426dd96
--- /dev/null
+++ b/lib/src/content_hash.rs
@@ -0,0 +1,221 @@
+use itertools::Itertools as _;
+
+/// Portable, stable hashing suitable for identifying values
+///
+/// Variable-length sequences should hash a 64-bit little-endian representation
+/// of their length, then their elements in order. Unordered containers should
+/// order their elements according to their `Ord` implementation. Enums should
+/// hash a 32-bit little-endian encoding of the ordinal number of the enum
+/// variant, then the variant's fields in lexical order.
+pub trait ContentHash {
+    fn hash(&self, state: &mut impl digest::Update);
+}
+
+impl ContentHash for () {
+    fn hash(&self, _: &mut impl digest::Update) {}
+}
+
+impl ContentHash for u8 {
+    fn hash(&self, state: &mut impl digest::Update) {
+        state.update(&[*self]);
+    }
+}
+
+impl ContentHash for i32 {
+    fn hash(&self, state: &mut impl digest::Update) {
+        state.update(&self.to_le_bytes());
+    }
+}
+
+impl ContentHash for i64 {
+    fn hash(&self, state: &mut impl digest::Update) {
+        state.update(&self.to_le_bytes());
+    }
+}
+
+// TODO: Specialize for [u8] once specialization exists
+impl<T: ContentHash> ContentHash for [T] {
+    fn hash(&self, state: &mut impl digest::Update) {
+        state.update(&(self.len() as u64).to_le_bytes());
+        for x in self {
+            x.hash(state);
+        }
+    }
+}
+
+impl<T: ContentHash> ContentHash for Vec<T> {
+    fn hash(&self, state: &mut impl digest::Update) {
+        self.as_slice().hash(state)
+    }
+}
+
+impl ContentHash for String {
+    fn hash(&self, state: &mut impl digest::Update) {
+        self.as_bytes().hash(state);
+    }
+}
+
+impl<T: ContentHash> ContentHash for Option<T> {
+    fn hash(&self, state: &mut impl digest::Update) {
+        match *self {
+            None => state.update(&[0]),
+            Some(ref x) => {
+                state.update(&[1]);
+                x.hash(state)
+            }
+        }
+    }
+}
+
+impl<K, V> ContentHash for std::collections::HashMap<K, V>
+where
+    K: ContentHash + Ord,
+    V: ContentHash,
+{
+    fn hash(&self, state: &mut impl digest::Update) {
+        state.update(&(self.len() as u64).to_le_bytes());
+        let mut kv = self.iter().collect_vec();
+        kv.sort_unstable_by_key(|&(k, _)| k);
+        for (k, v) in kv {
+            k.hash(state);
+            v.hash(state);
+        }
+    }
+}
+
+impl<K> ContentHash for std::collections::HashSet<K>
+where
+    K: ContentHash + Ord,
+{
+    fn hash(&self, state: &mut impl digest::Update) {
+        state.update(&(self.len() as u64).to_le_bytes());
+        for k in self.iter().sorted() {
+            k.hash(state);
+        }
+    }
+}
+
+impl<K, V> ContentHash for std::collections::BTreeMap<K, V>
+where
+    K: ContentHash,
+    V: ContentHash,
+{
+    fn hash(&self, state: &mut impl digest::Update) {
+        state.update(&(self.len() as u64).to_le_bytes());
+        for (k, v) in self.iter() {
+            k.hash(state);
+            v.hash(state);
+        }
+    }
+}
+
+macro_rules! content_hash {
+    ($(#[$meta:meta])* $vis:vis struct $name:ident {
+        $($(#[$field_meta:meta])* $field_vis:vis $field:ident : $ty:ty),* $(,)?
+    }) => {
+        $(#[$meta])*
+        $vis struct $name {
+            $($(#[$field_meta])* $field_vis $field : $ty),*
+        }
+
+        impl crate::content_hash::ContentHash for $name {
+            fn hash(&self, state: &mut impl digest::Update) {
+                $(<$ty as crate::content_hash::ContentHash>::hash(&self.$field, state);)*
+            }
+        }
+    };
+    ($(#[$meta:meta])* $vis:vis struct $name:ident($field_vis:vis $ty:ty);) => {
+        $(#[$meta])*
+        $vis struct $name($field_vis $ty);
+
+        impl crate::content_hash::ContentHash for $name {
+            fn hash(&self, state: &mut impl digest::Update) {
+                <$ty as crate::content_hash::ContentHash>::hash(&self.0, state);
+            }
+        }
+    };
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::{BTreeMap, HashMap};
+
+    use blake2::{Blake2b512, Digest};
+
+    use super::*;
+
+    #[test]
+    fn test_string_sanity() {
+        let a = "a".to_string();
+        let b = "b".to_string();
+        assert_eq!(hash(&a), hash(&a.clone()));
+        assert_ne!(hash(&a), hash(&b));
+        assert_ne!(hash(&"a".to_string()), hash(&"a\0".to_string()));
+    }
+
+    #[test]
+    fn test_hash_map_key_value_distinction() {
+        let a = [("ab".to_string(), "cd".to_string())]
+            .into_iter()
+            .collect::<HashMap<_, _>>();
+        let b = [("a".to_string(), "bcd".to_string())]
+            .into_iter()
+            .collect::<HashMap<_, _>>();
+
+        assert_ne!(hash(&a), hash(&b));
+    }
+
+    #[test]
+    fn test_btree_map_key_value_distinction() {
+        let a = [("ab".to_string(), "cd".to_string())]
+            .into_iter()
+            .collect::<BTreeMap<_, _>>();
+        let b = [("a".to_string(), "bcd".to_string())]
+            .into_iter()
+            .collect::<BTreeMap<_, _>>();
+
+        assert_ne!(hash(&a), hash(&b));
+    }
+
+    #[test]
+    fn test_struct_sanity() {
+        content_hash! {
+            struct Foo { x: i32 }
+        }
+        assert_ne!(hash(&Foo { x: 42 }), hash(&Foo { x: 12 }));
+    }
+
+    #[test]
+    fn test_option_sanity() {
+        assert_ne!(hash(&Some(42)), hash(&42));
+        assert_ne!(hash(&None::<i32>), hash(&42i32));
+    }
+
+    #[test]
+    fn test_slice_sanity() {
+        assert_ne!(hash(&[42i32][..]), hash(&[12i32][..]));
+        assert_ne!(hash(&([] as [i32; 0])[..]), hash(&[42i32][..]));
+        assert_ne!(hash(&([] as [i32; 0])[..]), hash(&()));
+        assert_ne!(hash(&42i32), hash(&[42i32][..]));
+    }
+
+    #[test]
+    fn test_consistent_hashing() {
+        content_hash! {
+            struct Foo { x: Vec<Option<i32>>, y: i64 }
+        }
+        insta::assert_snapshot!(
+            hex::encode(&hash(&Foo {
+                x: vec![None, Some(42)],
+                y: 17
+            })),
+            @"14e42ea3d680bc815d0cea8ac20d3e872120014fb7bba8d82c3ffa7a8e6d63c41ef9631c60b73b150e3dd72efe50e8b0248321fe2b7eea09d879f3757b879372"
+        );
+    }
+
+    fn hash(x: &(impl ContentHash + ?Sized)) -> digest::Output<Blake2b512> {
+        let mut hasher = Blake2b512::default();
+        x.hash(&mut hasher);
+        hasher.finalize()
+    }
+}
diff --git a/lib/src/lib.rs b/lib/src/lib.rs
index a7053967630..612285aa5e6 100644
--- a/lib/src/lib.rs
+++ b/lib/src/lib.rs
@@ -14,6 +14,9 @@
 
 #![deny(unused_must_use)]
 
+#[macro_use]
+mod content_hash;
+
 pub mod backend;
 pub mod commit;
 pub mod commit_builder;
diff --git a/lib/src/op_store.rs b/lib/src/op_store.rs
index 3d74c7f555b..1e7387fe6c0 100644
--- a/lib/src/op_store.rs
+++ b/lib/src/op_store.rs
@@ -18,9 +18,12 @@ use std::fmt::{Debug, Error, Formatter};
 use thiserror::Error;
 
 use crate::backend::{CommitId, Timestamp};
+use crate::content_hash::ContentHash;
 
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
-pub struct WorkspaceId(String);
+content_hash! {
+    #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
+    pub struct WorkspaceId(String);
+}
 
 impl Debug for WorkspaceId {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
@@ -44,8 +47,10 @@ impl WorkspaceId {
     }
 }
 
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
-pub struct ViewId(Vec<u8>);
+content_hash! {
+    #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
+    pub struct ViewId(Vec<u8>);
+}
 
 impl Debug for ViewId {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
@@ -75,8 +80,10 @@ impl ViewId {
     }
 }
 
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
-pub struct OperationId(Vec<u8>);
+content_hash! {
+    #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
+    pub struct OperationId(Vec<u8>);
+}
 
 impl Debug for OperationId {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
@@ -115,6 +122,26 @@ pub enum RefTarget {
     },
 }
 
+impl ContentHash for RefTarget {
+    fn hash(&self, state: &mut impl digest::Update) {
+        use RefTarget::*;
+        match *self {
+            Normal(ref id) => {
+                state.update(&0u32.to_le_bytes());
+                id.hash(state);
+            }
+            Conflict {
+                ref removes,
+                ref adds,
+            } => {
+                state.update(&1u32.to_le_bytes());
+                removes.hash(state);
+                adds.hash(state);
+            }
+        }
+    }
+}
+
 impl RefTarget {
     pub fn is_conflict(&self) -> bool {
         matches!(self, RefTarget::Conflict { .. })
@@ -146,67 +173,75 @@ impl RefTarget {
     }
 }
 
-#[derive(Default, PartialEq, Eq, Clone, Debug)]
-pub struct BranchTarget {
-    /// The commit the branch points to locally. `None` if the branch has been
-    /// deleted locally.
-    pub local_target: Option<RefTarget>,
-    // TODO: Do we need to support tombstones for remote branches? For example, if the branch
-    // has been deleted locally and you pull from a remote, maybe it should make a difference
-    // whether the branch is known to have existed on the remote. We may not want to resurrect
-    // the branch if the branch's state on the remote was just not known.
-    pub remote_targets: BTreeMap<String, RefTarget>,
-}
-
-/// Represents the way the repo looks at a given time, just like how a Tree
-/// object represents how the file system looks at a given time.
-#[derive(PartialEq, Eq, Clone, Debug, Default)]
-pub struct View {
-    /// All head commits
-    pub head_ids: HashSet<CommitId>,
-    /// Heads of the set of public commits.
-    pub public_head_ids: HashSet<CommitId>,
-    pub branches: BTreeMap<String, BranchTarget>,
-    pub tags: BTreeMap<String, RefTarget>,
-    pub git_refs: BTreeMap<String, RefTarget>,
-    /// The commit the Git HEAD points to.
-    // TODO: Support multiple Git worktrees?
-    // TODO: Do we want to store the current branch name too?
-    pub git_head: Option<CommitId>,
-    // The commit that *should be* checked out in the workspace. Note that the working copy
-    // (.jj/working_copy/) has the source of truth about which commit *is* checked out (to be
-    // precise: the commit to which we most recently completed an update to).
-    pub wc_commit_ids: HashMap<WorkspaceId, CommitId>,
-}
-
-/// Represents an operation (transaction) on the repo view, just like how a
-/// Commit object represents an operation on the tree.
-///
-/// Operations and views are not meant to be exchanged between repos or users;
-/// they represent local state and history.
-///
-/// The operation history will almost always be linear. It will only have
-/// forks when parallel operations occurred. The parent is determined when
-/// the transaction starts. When the transaction commits, a lock will be
-/// taken and it will be checked that the current head of the operation
-/// graph is unchanged. If the current head has changed, there has been
-/// concurrent operation.
-#[derive(PartialEq, Eq, Clone, Debug)]
-pub struct Operation {
-    pub view_id: ViewId,
-    pub parents: Vec<OperationId>,
-    pub metadata: OperationMetadata,
+content_hash! {
+    #[derive(Default, PartialEq, Eq, Clone, Debug)]
+    pub struct BranchTarget {
+        /// The commit the branch points to locally. `None` if the branch has been
+        /// deleted locally.
+        pub local_target: Option<RefTarget>,
+        // TODO: Do we need to support tombstones for remote branches? For example, if the branch
+        // has been deleted locally and you pull from a remote, maybe it should make a difference
+        // whether the branch is known to have existed on the remote. We may not want to resurrect
+        // the branch if the branch's state on the remote was just not known.
+        pub remote_targets: BTreeMap<String, RefTarget>,
+    }
 }
 
-#[derive(PartialEq, Eq, Clone, Debug)]
-pub struct OperationMetadata {
-    pub start_time: Timestamp,
-    pub end_time: Timestamp,
-    // Whatever is useful to the user, such as exact command line call
-    pub description: String,
-    pub hostname: String,
-    pub username: String,
-    pub tags: HashMap<String, String>,
+content_hash! {
+    /// Represents the way the repo looks at a given time, just like how a Tree
+    /// object represents how the file system looks at a given time.
+    #[derive(PartialEq, Eq, Clone, Debug, Default)]
+    pub struct View {
+        /// All head commits
+        pub head_ids: HashSet<CommitId>,
+        /// Heads of the set of public commits.
+        pub public_head_ids: HashSet<CommitId>,
+        pub branches: BTreeMap<String, BranchTarget>,
+        pub tags: BTreeMap<String, RefTarget>,
+        pub git_refs: BTreeMap<String, RefTarget>,
+        /// The commit the Git HEAD points to.
+        // TODO: Support multiple Git worktrees?
+        // TODO: Do we want to store the current branch name too?
+        pub git_head: Option<CommitId>,
+        // The commit that *should be* checked out in the workspace. Note that the working copy
+        // (.jj/working_copy/) has the source of truth about which commit *is* checked out (to be
+        // precise: the commit to which we most recently completed an update to).
+        pub wc_commit_ids: HashMap<WorkspaceId, CommitId>,
+    }
+}
+
+content_hash! {
+    /// Represents an operation (transaction) on the repo view, just like how a
+    /// Commit object represents an operation on the tree.
+    ///
+    /// Operations and views are not meant to be exchanged between repos or users;
+    /// they represent local state and history.
+    ///
+    /// The operation history will almost always be linear. It will only have
+    /// forks when parallel operations occurred. The parent is determined when
+    /// the transaction starts. When the transaction commits, a lock will be
+    /// taken and it will be checked that the current head of the operation
+    /// graph is unchanged. If the current head has changed, there has been
+    /// concurrent operation.
+    #[derive(PartialEq, Eq, Clone, Debug)]
+    pub struct Operation {
+        pub view_id: ViewId,
+        pub parents: Vec<OperationId>,
+        pub metadata: OperationMetadata,
+    }
+}
+
+content_hash! {
+    #[derive(PartialEq, Eq, Clone, Debug)]
+    pub struct OperationMetadata {
+        pub start_time: Timestamp,
+        pub end_time: Timestamp,
+        // Whatever is useful to the user, such as exact command line call
+        pub description: String,
+        pub hostname: String,
+        pub username: String,
+        pub tags: HashMap<String, String>,
+    }
 }
 
 impl OperationMetadata {
diff --git a/lib/src/simple_op_store.rs b/lib/src/simple_op_store.rs
index 372b19cff58..54a950184e3 100644
--- a/lib/src/simple_op_store.rs
+++ b/lib/src/simple_op_store.rs
@@ -16,15 +16,16 @@ use std::collections::BTreeMap;
 use std::fmt::Debug;
 use std::fs;
 use std::fs::File;
-use std::io::{ErrorKind, Write};
+use std::io::ErrorKind;
 use std::path::PathBuf;
 
-use blake2::{Blake2b512, Digest};
+use blake2::Blake2b512;
 use itertools::Itertools;
 use protobuf::{Message, MessageField};
 use tempfile::{NamedTempFile, PersistError};
 
 use crate::backend::{CommitId, MillisSinceEpoch, Timestamp};
+use crate::content_hash::ContentHash;
 use crate::file_util::persist_content_addressed_temp_file;
 use crate::op_store::{
     BranchTarget, OpStore, OpStoreError, OpStoreResult, Operation, OperationId, OperationMetadata,
@@ -95,12 +96,9 @@ impl OpStore for SimpleOpStore {
         let temp_file = NamedTempFile::new_in(&self.path)?;
 
         let proto = view_to_proto(view);
-        let mut proto_bytes: Vec<u8> = Vec::new();
-        proto.write_to_writer(&mut proto_bytes)?;
+        proto.write_to_writer(&mut temp_file.as_file())?;
 
-        temp_file.as_file().write_all(&proto_bytes)?;
-
-        let id = ViewId::new(Blake2b512::digest(&proto_bytes).to_vec());
+        let id = ViewId::new(hash(view).to_vec());
 
         persist_content_addressed_temp_file(temp_file, self.view_path(&id))?;
         Ok(id)
@@ -118,12 +116,9 @@ impl OpStore for SimpleOpStore {
         let temp_file = NamedTempFile::new_in(&self.path)?;
 
         let proto = operation_to_proto(operation);
-        let mut proto_bytes: Vec<u8> = Vec::new();
-        proto.write_to_writer(&mut proto_bytes)?;
-
-        temp_file.as_file().write_all(&proto_bytes)?;
+        proto.write_to_writer(&mut temp_file.as_file())?;
 
-        let id = OperationId::new(Blake2b512::digest(&proto_bytes).to_vec());
+        let id = OperationId::new(hash(operation).to_vec());
 
         persist_content_addressed_temp_file(temp_file, self.operation_path(&id))?;
         Ok(id)
@@ -363,6 +358,13 @@ fn ref_target_from_proto(proto: &crate::protos::op_store::RefTarget) -> RefTarge
     }
 }
 
+fn hash(x: &impl ContentHash) -> digest::Output<Blake2b512> {
+    use digest::Digest;
+    let mut hasher = Blake2b512::default();
+    x.hash(&mut hasher);
+    hasher.finalize()
+}
+
 #[cfg(test)]
 mod tests {
     use maplit::{btreemap, hashmap, hashset};