cli: add --no-cache option (#157)

This is useful for CI where you don't care about eval caching. And avoid
the issue described in #156.

README.md

@@ -47,10 +47,11 @@ USAGE:
     treefmt [FLAGS] [OPTIONS] [paths]...
 
 FLAGS:
-        --clear-cache       Clear the evaluation cache. Use in case the cache is not precise enough
+        --clear-cache       Reset the evaluation cache. Use in case the cache is not precise enough
         --fail-on-change    Exit with error if any changes were made. Useful for CI
     -h, --help              Prints help information
         --init              Create a new treefmt.toml
+        --no-cache          Ignore the evaluation cache entirely. Useful for CI
     -q, --quiet             No output printed to stderr
         --stdin             Format the content passed in stdin
     -V, --version           Prints version information

src/command/format.rs

@@ -10,6 +10,7 @@ pub fn format_cmd(
     work_dir: &Path,
     config_file: &Path,
     paths: &[PathBuf],
+    no_cache: bool,
     clear_cache: bool,
     fail_on_change: bool,
 ) -> anyhow::Result<()> {
@@ -55,6 +56,7 @@ pub fn format_cmd(
         &cache_dir,
         config_file,
         &paths,
+        no_cache,
         clear_cache,
         fail_on_change,
     )?;

src/command/mod.rs

@@ -25,7 +25,11 @@ pub struct Cli {
     #[structopt(long = "stdin", conflicts_with("init"))]
     pub stdin: bool,
 
-    /// Clear the evaluation cache. Use in case the cache is not precise enough.
+    /// Ignore the evaluation cache entirely. Useful for CI.
+    #[structopt(long = "no-cache", conflicts_with("stdin"), conflicts_with("init"))]
+    pub no_cache: bool,
+
+    /// Reset the evaluation cache. Use in case the cache is not precise enough.
     #[structopt(long = "clear-cache", conflicts_with("stdin"), conflicts_with("init"))]
     pub clear_cache: bool,
 
@@ -122,6 +126,7 @@ pub fn run_cli(cli: &Cli) -> anyhow::Result<()> {
                 .as_ref()
                 .expect("presence asserted in ::cli_from_args"),
             &cli.paths,
+            cli.no_cache,
             cli.clear_cache,
             cli.fail_on_change,
         )?

src/engine.rs

@@ -26,6 +26,7 @@ pub fn run_treefmt(
     cache_dir: &Path,
     treefmt_toml: &Path,
     paths: &[PathBuf],
+    no_cache: bool,
     clear_cache: bool,
     fail_on_change: bool,
 ) -> anyhow::Result<()> {
@@ -98,15 +99,18 @@ pub fn run_treefmt(
     timed_debug("load formatters");
 
     // Load the eval cache
-    let mut cache = if clear_cache {
+    let mut cache = if no_cache || clear_cache {
         // Start with an empty cache
         CacheManifest::default()
     } else {
         CacheManifest::load(cache_dir, treefmt_toml)
     };
     timed_debug("load cache");
-    // Insert the new formatter configs
-    cache.update_formatters(formatters.clone());
+
+    if !no_cache {
+        // Insert the new formatter configs
+        cache.update_formatters(formatters.clone());
+    }
 
     // Configure the tree walker
     let walker = {
@@ -168,7 +172,11 @@ pub fn run_treefmt(
     timed_debug("tree walk");
 
     // Filter out all of the paths that were already in the cache
-    let matches = cache.filter_matches(matches);
+    let matches = if !no_cache {
+        cache.filter_matches(matches)
+    } else {
+        matches
+    };
 
     timed_debug("filter_matches");
 
@@ -219,11 +227,13 @@ pub fn run_treefmt(
         .collect::<anyhow::Result<BTreeMap<FormatterName, BTreeMap<PathBuf, FileMeta>>>>()?;
     timed_debug("format");
 
-    // Record the new matches in the cache
-    cache.add_results(new_matches.clone());
-    // And write to disk
-    cache.write(cache_dir, treefmt_toml);
-    timed_debug("write cache");
+    if !no_cache {
+        // Record the new matches in the cache
+        cache.add_results(new_matches.clone());
+        // And write to disk
+        cache.write(cache_dir, treefmt_toml);
+        timed_debug("write cache");
+    }
 
     // Diff the old matches with the new matches
     let changed_matches: BTreeMap<FormatterName, Vec<PathBuf>> =