Making caching support optional in Wasmtime (#2119)

This commit moves all of the caching support that currently lives in
`wasmtime-environ` into a `wasmtime-cache` crate and makes it optional. The
goal here is to slim down the `wasmtime-environ` crate and clearly separate
boundaries where caching is a standalone and optional feature, not intertwined
with other crates.

crates/cache/src/tests.rs

@@ -0,0 +1,92 @@
+use super::config::tests::test_prolog;
+use super::*;
+use std::fs;
+
+// Since cache system is a global thing, each test needs to be run in seperate process.
+// So, init() tests are run as integration tests.
+// However, caching is a private thing, an implementation detail, and needs to be tested
+// from the inside of the module.
+// We test init() in exactly one test, rest of the tests doesn't rely on it.
+
+#[test]
+fn test_cache_init() {
+    let (_tempdir, cache_dir, config_path) = test_prolog();
+    let baseline_compression_level = 4;
+    let config_content = format!(
+        "[cache]\n\
+         enabled = true\n\
+         directory = {}\n\
+         baseline-compression-level = {}\n",
+        toml::to_string_pretty(&format!("{}", cache_dir.display())).unwrap(),
+        baseline_compression_level,
+    );
+    fs::write(&config_path, config_content).expect("Failed to write test config file");
+
+    let cache_config = CacheConfig::from_file(Some(&config_path)).unwrap();
+
+    // test if we can use config
+    assert!(cache_config.enabled());
+    // assumption: config init creates cache directory and returns canonicalized path
+    assert_eq!(
+        *cache_config.directory(),
+        fs::canonicalize(cache_dir).unwrap()
+    );
+    assert_eq!(
+        cache_config.baseline_compression_level(),
+        baseline_compression_level
+    );
+
+    // test if we can use worker
+    cache_config.worker().on_cache_update_async(config_path);
+}
+
+#[test]
+fn test_write_read_cache() {
+    let (_tempdir, cache_dir, config_path) = test_prolog();
+    let cache_config = load_config!(
+        config_path,
+        "[cache]\n\
+         enabled = true\n\
+         directory = {cache_dir}\n\
+         baseline-compression-level = 3\n",
+        cache_dir
+    );
+    assert!(cache_config.enabled());
+
+    // assumption: config load creates cache directory and returns canonicalized path
+    assert_eq!(
+        *cache_config.directory(),
+        fs::canonicalize(cache_dir).unwrap()
+    );
+
+    let compiler1 = "test-1";
+    let compiler2 = "test-2";
+
+    let entry1 = ModuleCacheEntry::from_inner(ModuleCacheEntryInner::new(compiler1, &cache_config));
+    let entry2 = ModuleCacheEntry::from_inner(ModuleCacheEntryInner::new(compiler2, &cache_config));
+
+    entry1.get_data::<_, i32, i32>(1, |_| Ok(100)).unwrap();
+    entry1.get_data::<_, i32, i32>(1, |_| panic!()).unwrap();
+
+    entry1.get_data::<_, i32, i32>(2, |_| Ok(100)).unwrap();
+    entry1.get_data::<_, i32, i32>(1, |_| panic!()).unwrap();
+    entry1.get_data::<_, i32, i32>(2, |_| panic!()).unwrap();
+
+    entry1.get_data::<_, i32, i32>(3, |_| Ok(100)).unwrap();
+    entry1.get_data::<_, i32, i32>(1, |_| panic!()).unwrap();
+    entry1.get_data::<_, i32, i32>(2, |_| panic!()).unwrap();
+    entry1.get_data::<_, i32, i32>(3, |_| panic!()).unwrap();
+
+    entry1.get_data::<_, i32, i32>(4, |_| Ok(100)).unwrap();
+    entry1.get_data::<_, i32, i32>(1, |_| panic!()).unwrap();
+    entry1.get_data::<_, i32, i32>(2, |_| panic!()).unwrap();
+    entry1.get_data::<_, i32, i32>(3, |_| panic!()).unwrap();
+    entry1.get_data::<_, i32, i32>(4, |_| panic!()).unwrap();
+
+    entry2.get_data::<_, i32, i32>(1, |_| Ok(100)).unwrap();
+    entry1.get_data::<_, i32, i32>(1, |_| panic!()).unwrap();
+    entry1.get_data::<_, i32, i32>(2, |_| panic!()).unwrap();
+    entry1.get_data::<_, i32, i32>(3, |_| panic!()).unwrap();
+    entry1.get_data::<_, i32, i32>(4, |_| panic!()).unwrap();
+    entry2.get_data::<_, i32, i32>(1, |_| panic!()).unwrap();
+}