Add logging feature to enable optional log crate dependency

.github/workflows/CI.yml

@@ -88,11 +88,11 @@ jobs:
           command: test
           args: --no-default-features --features 'future, atomic64, quanta'
 
-      - name: Run tests (future and sync features)
+      - name: Run tests (future, sync and logging features)
         uses: actions-rs/cargo@v1
         with:
           command: test
-          args: --features 'future, sync'
+          args: --features 'future, sync, logging'
 
       - name: Run tests (dash feature, but no sync feature)
         uses: actions-rs/cargo@v1

.github/workflows/CIQuantaDisabled.yml

@@ -82,11 +82,11 @@ jobs:
           command: test
           args: --no-default-features --features 'future, atomic64'
 
-      - name: Run tests (future feature, but no quanta feature)
+      - name: Run tests (future, sync and logging features, but no quanta feature)
         uses: actions-rs/cargo@v1
         with:
           command: test
-          args: --no-default-features --features 'sync, future, atomic64'
+          args: --no-default-features --features 'sync, future, atomic64, logging'
 
       - name: Run tests (dash feature, but no quanta and sync features)
         uses: actions-rs/cargo@v1

Cargo.toml

@@ -30,6 +30,11 @@ future = ["crossbeam-epoch", "thiserror", "uuid", "async-io", "async-lock", "fut
 # few releases.
 dash = ["dashmap"]
 
+# Enable this feature to activate optional logging from caches.
+# Currently cache will emit log only when it encounters a panic in user provided
+# callback closure.
+logging = ["log"]
+
 # This feature is enabled by default. Disable it when the target platform does not
 # support `std::sync::atomic::AtomicU64`. (e.g. `armv5te-unknown-linux-musleabi`
 # or `mips-unknown-linux-musl`)
@@ -73,6 +78,9 @@ async-io = { version = "1.4", optional = true }
 async-lock = { version = "2.4", optional = true }
 futures-util = { version = "0.3", optional = true }
 
+# Optional dependencies (logging)
+log = { version = "0.4", optional = true }
+
 [dev-dependencies]
 actix-rt = { version = "2.7", default-features = false }
 async-std = { version = "1.11", features = ["attributes"] }