Merge #264: Virtual hidden nodes

29dd9ea refactor: Remove Error::DisconnectCommitTime (Christian Lewe)
cdf28e0 refactor: Simplify policy satisfier (Christian Lewe)
ba5c7ef fix: Handle missing assembly fragments (Christian Lewe)
d79c6bc feat: Add Hiding node (Christian Lewe)
776b23c feat: Add HasCmr trait (Christian Lewe)
7d862b8 fix: Update fuzz CI (Christian Lewe)

Pull request description:

  This PR adds the wrapper type `Hiding<N>` which allows the use of hidden nodes during the construction of a program. The hidden nodes exist only in the wrapper and the `Inner` struct remains untouched _(therefore "virtual hidden nodes")_.

  We use `Hiding<N>` to simplify the policy satisfier and to represent missing assembly fragments, which removes one error path.

ACKs for top commit:
  apoelstra:
    ACK 29dd9ea; successfully ran local tests; awesome, thanks!

Tree-SHA512: 1ea6d93cfdbfb8af91b7702debf66c36354dc19c54efd36db49c81ee5bc55d227056914b44e158431021ab3d51771a2becb5380aea1ed5fc367b16d226b6b423

Author: apoelstra

.github/workflows/fuzz.yml

@@ -10,6 +10,7 @@ on:
 
 jobs:
   fuzz:
+    name: Run Fuzz Target
     if: ${{ !github.event.act }}
     runs-on: ubuntu-latest
     strategy:
@@ -24,36 +25,55 @@ parse_human,
     steps:
       - name: Install test dependencies
         run: sudo apt-get update -y && sudo apt-get install -y binutils-dev libunwind8-dev libcurl4-openssl-dev libelf-dev libdw-dev cmake gcc libiberty-dev
-      - uses: actions/checkout@v4
-      - uses: actions/cache@v3
+
+      - name: Checkout Crate
+        uses: actions/checkout@v4
+
+      - name: Use Rust Cache
+        uses: actions/cache@v4
         id: cache-fuzz
         with:
           path: |
             ~/.cargo/bin
             fuzz/target
             target
           key: cache-${{ matrix.target }}-${{ hashFiles('**/Cargo.toml','**/Cargo.lock') }}
-      - uses: dtolnay/rust-toolchain@stable
+      - name: Install Toolchain
+        uses: dtolnay/rust-toolchain@stable
         with:
           toolchain: '1.65.0'
-      - name: fuzz
+
+      - name: Run Fuzz Target
         run: |
           echo "Using RUSTFLAGS $RUSTFLAGS"
           cd fuzz && cargo update && cargo update -p cc --precise 1.0.83 && ./fuzz.sh "${{ matrix.fuzz_target }}"
-      - run: echo "${{ matrix.fuzz_target }}" >executed_${{ matrix.fuzz_target }}
-      - uses: actions/upload-artifact@v3
+
+      - name: Prepare Artifact
+        run: echo "${{ matrix.fuzz_target }}" >executed_${{ matrix.fuzz_target }}
+
+      - name: Upload Artifact
+        uses: actions/upload-artifact@v4
         with:
           name: executed_${{ matrix.fuzz_target }}
           path: executed_${{ matrix.fuzz_target }}
 
   verify-execution:
+    name: Verify Execution of All Targets
     if: ${{ !github.event.act }}
     needs: fuzz
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/download-artifact@v3
-      - name: Display structure of downloaded files
+      - name: Checkout Crate
+        uses: actions/checkout@v4
+
+      - name: Download All Artifacts
+        uses: actions/download-artifact@v4
+
+      - name: Display Structure of Downloaded Files
         run: ls -R
-      - run: find executed_* -type f -exec cat {} + | sort > executed
-      - run: source ./fuzz/fuzz-util.sh && listTargetNames | sort | diff - executed
+
+      - name: Write File With All Executed Targets
+        run: find executed_* -type f -exec cat {} + | sort > executed
+
+      - name: Compare Executed Targets With Available Targets
+        run: source ./fuzz/fuzz-util.sh && listTargetNames | sort | diff - executed

fuzz/generate-files.sh

@@ -49,6 +49,7 @@ on:
 
 jobs:
   fuzz:
+    name: Run Fuzz Target
     if: \${{ !github.event.act }}
     runs-on: ubuntu-latest
     strategy:
@@ -60,37 +61,56 @@ $(for name in $(listTargetNames); do echo "$name,"; done)
     steps:
       - name: Install test dependencies
         run: sudo apt-get update -y && sudo apt-get install -y binutils-dev libunwind8-dev libcurl4-openssl-dev libelf-dev libdw-dev cmake gcc libiberty-dev
-      - uses: actions/checkout@v4
-      - uses: actions/cache@v3
+
+      - name: Checkout Crate
+        uses: actions/checkout@v4
+
+      - name: Use Rust Cache
+        uses: actions/cache@v4
         id: cache-fuzz
         with:
           path: |
             ~/.cargo/bin
             fuzz/target
             target
           key: cache-\${{ matrix.target }}-\${{ hashFiles('**/Cargo.toml','**/Cargo.lock') }}
-      - uses: dtolnay/rust-toolchain@stable
+      - name: Install Toolchain
+        uses: dtolnay/rust-toolchain@stable
         with:
           toolchain: '1.65.0'
-      - name: fuzz
+
+      - name: Run Fuzz Target
         run: |
           echo "Using RUSTFLAGS \$RUSTFLAGS"
           cd fuzz && cargo update && cargo update -p cc --precise 1.0.83 && ./fuzz.sh "\${{ matrix.fuzz_target }}"
-      - run: echo "\${{ matrix.fuzz_target }}" >executed_\${{ matrix.fuzz_target }}
-      - uses: actions/upload-artifact@v3
+
+      - name: Prepare Artifact
+        run: echo "\${{ matrix.fuzz_target }}" >executed_\${{ matrix.fuzz_target }}
+
+      - name: Upload Artifact
+        uses: actions/upload-artifact@v4
         with:
           name: executed_\${{ matrix.fuzz_target }}
           path: executed_\${{ matrix.fuzz_target }}
 
   verify-execution:
+    name: Verify Execution of All Targets
     if: \${{ !github.event.act }}
     needs: fuzz
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/download-artifact@v3
-      - name: Display structure of downloaded files
+      - name: Checkout Crate
+        uses: actions/checkout@v4
+
+      - name: Download All Artifacts
+        uses: actions/download-artifact@v4
+
+      - name: Display Structure of Downloaded Files
         run: ls -R
-      - run: find executed_* -type f -exec cat {} + | sort > executed
-      - run: source ./fuzz/fuzz-util.sh && listTargetNames | sort | diff - executed
+
+      - name: Write File With All Executed Targets
+        run: find executed_* -type f -exec cat {} + | sort > executed
+
+      - name: Compare Executed Targets With Available Targets
+        run: source ./fuzz/fuzz-util.sh && listTargetNames | sort | diff - executed
 EOF

src/lib.rs

@@ -59,9 +59,9 @@ pub use crate::merkle::{
     cmr::Cmr,
     imr::{FirstPassImr, Imr},
     tmr::Tmr,
-    FailEntropy,
+    FailEntropy, HasCmr,
 };
-pub use crate::node::{CommitNode, ConstructNode, RedeemNode, WitnessNode};
+pub use crate::node::{CommitNode, ConstructNode, Hiding, RedeemNode, WitnessNode};
 pub use crate::value::{Value, Word};
 pub use simplicity_sys as ffi;
 use std::fmt;
@@ -78,8 +78,6 @@ pub fn leaf_version() -> elements::taproot::LeafVersion {
 pub enum Error {
     /// Decoder error
     Decode(decode::Error),
-    /// A disconnect node was populated at commitment time
-    DisconnectCommitTime,
     /// A disconnect node was *not* populated at redeem time
     DisconnectRedeemTime,
     /// Type-checking error
@@ -99,9 +97,6 @@ impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
             Error::Decode(ref e) => fmt::Display::fmt(e, f),
-            Error::DisconnectCommitTime => {
-                f.write_str("disconnect node had two children (commit time); must have one")
-            }
             Error::DisconnectRedeemTime => {
                 f.write_str("disconnect node had one child (redeem time); must have two")
             }
@@ -119,7 +114,6 @@ impl std::error::Error for Error {
     fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
         match *self {
             Error::Decode(ref e) => Some(e),
-            Error::DisconnectCommitTime => None,
             Error::DisconnectRedeemTime => None,
             Error::Type(ref e) => Some(e),
             Error::Execution(ref e) => Some(e),

src/merkle/mod.rs

@@ -15,6 +15,12 @@ use crate::Value;
 use hashes::{sha256, Hash, HashEngine};
 use std::fmt;
 
+/// Trait for types that have a Commitment Merkle Root.
+pub trait HasCmr {
+    /// Access the Commitment Merkle Root.
+    fn cmr(&self) -> cmr::Cmr;
+}
+
 /// 512-bit opaque blob of data used to seed `Fail` nodes
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
 pub struct FailEntropy([u8; 64]);

src/node/construct.rs

@@ -98,14 +98,10 @@ impl<J: Jet> ConstructNode<J> {
             fn convert_disconnect(
                 &mut self,
                 _: &PostOrderIterItem<&ConstructNode<J>>,
-                maybe_converted: Option<&Arc<CommitNode<J>>>,
+                _: Option<&Arc<CommitNode<J>>>,
                 _: &Option<Arc<ConstructNode<J>>>,
             ) -> Result<NoDisconnect, Self::Error> {
-                if maybe_converted.is_some() {
-                    Err(crate::Error::DisconnectCommitTime)
-                } else {
-                    Ok(NoDisconnect)
-                }
+                Ok(NoDisconnect)
             }
 
             fn convert_data(