Add an optional Soufflé backend

.github/workflows/ci.yml

@@ -4,7 +4,7 @@ on:
   push:
     branches: [ master ]
   pull_request:
-    
+
 jobs:
   rustfmt:
     name: Check formatting
@@ -56,11 +56,18 @@ jobs:
     strategy:
       matrix:
         rust: [beta, nightly]
+        features: [[], ['polonius-souffle']]
     steps:
       - uses: actions/checkout@v2
         with:
           fetch-depth: 1
 
+      - name: Install Souffle
+        if: contains(matrix.features, 'polonius-souffle')
+        run: |
+          wget https://github.com/ecstatic-morse/souffle/releases/download/2.0.2-alpha/souffle-2.0.2-Linux.deb
+          sudo apt install ./souffle-2.0.2-Linux.deb
+
       - name: Install rust toolchain
         uses: actions-rs/toolchain@v1
         with:
@@ -69,7 +76,11 @@ jobs:
           override: true
 
       - name: Build polonius
-        run: cargo build
+        run: cargo build --features "${{ join(matrix.features) }}"
+
+      - name: Execute tests for all crates in the workspace (except `polonius-souffle`)
+        run: cargo test --all --exclude polonius-souffle  --features "${{ join(matrix.features) }}"
 
-      - name: Execute tests for all crates in the workspace
-        run: cargo test --all
+      - name: Execute tests for `polonius-souffle`
+        if: contains(matrix.features, 'polonius-souffle')
+        run: cargo test -p polonius-souffle

Cargo.toml

@@ -4,20 +4,22 @@ version     = "0.7.0"
 authors     = ["The Rust Project Developers", "Polonius Developers"]
 description = "Core definition for the Rust borrow checker"
 license     = "Apache-2.0/MIT"
-repository  = "https://github.com/rust-lang/polonius"
+repository  = "https://github.com/rust-lang-nursery/polonius"
 readme      = "README.md"
 keywords    = ["compiler", "borrowck", "datalog"]
 edition     = "2018"
+resolver    = "2"
 
 [dev-dependencies]
 diff            = "0.1.0"
 polonius-parser = { path = "./polonius-parser" }
 
 [dependencies]
-rustc-hash      = "1.0.0"
-polonius-engine = { path = "./polonius-engine" }
-log             = "0.4"
-petgraph        = "0.4.13"
-pico-args       = "0.2"
+rustc-hash = "1.0.0"
+polonius-engine = { path = "polonius-engine" }
+polonius-souffle = { path = "polonius-souffle", optional = true }
+log = "0.4"
+petgraph = "0.4.13"
+pico-args = "0.2"
 
 [workspace]

polonius-engine/Cargo.toml

@@ -7,8 +7,11 @@ license = "Apache-2.0/MIT"
 repository = "https://github.com/rust-lang-nursery/polonius"
 readme = "README.md"
 keywords = ["compiler", "borrowck", "datalog"]
+resolver = "2"
 
 [dependencies]
 datafrog = "2.0.0"
+polonius-facts = { path = "../polonius-facts" }
+polonius-souffle = { path = "../polonius-souffle", optional = true }
 rustc-hash = "1.0.0"
 log = "0.4"