Misc: Hide criterion behind a flag to shorten CI time

Author: Serial-ATA

.github/workflows/bench.yml

@@ -23,6 +23,8 @@ jobs:
           override: true
 
       - name: Run benchmark
+        env:
+            RUSTFLAGS: "--cfg bench"
         run: cargo bench --all-features -- --output-format bencher | tee output.txt
 
       - name: Store benchmark result

Cargo.toml

@@ -41,13 +41,16 @@ aiff_text_chunks = []
 riff_info_list = []
 
 [dev-dependencies]
-criterion = { version = "0.4.0", features = ["html_reports"] }
 # WAV properties validity tests
 hound = { git = "https://github.com/ruuda/hound.git", rev = "02e66effb33683dd6acb92df792683ee46ad6a59" }
 # tag_writer example
 structopt = { version = "0.3.26", default-features = false }
 tempfile = "3.3.0"
 
+# Pretty heavy dependency, we don't want this compiling for test/doc runs
+[target.'cfg(bench)'.dev-dependencies]
+criterion = { version = "0.4.0", features = ["html_reports"] }
+
 [lib]
 bench = false
 

README.md

@@ -35,6 +35,17 @@ cargo run --example custom_resolver
 
 Available [here](https://docs.rs/lofty)
 
+## Benchmarking
+
+There are benchmarks available [here](./benches).
+
+These benchmarks make use of [criterion](https://github.com/bheisler/criterion.rs), and
+due to its size it cannot be a normal dev-dependency. To run the benchmarks do:
+
+```shell
+RUSTFLAGS="--cfg bench" cargo bench
+```
+
 ## License
 
 Licensed under either of