perf(fmt/lint): incremental formatting and linting (#14314)

Cargo.lock

@@ -795,6 +795,7 @@ dependencies = [
  "tower-lsp",
  "trust-dns-client",
  "trust-dns-server",
+ "twox-hash",
  "typed-arena",
  "uuid",
  "walkdir",
@@ -4723,6 +4724,17 @@ dependencies = [
  "webpki",
 ]
 
+[[package]]
+name = "twox-hash"
+version = "1.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4ee73e6e4924fe940354b8d4d98cad5231175d615cd855b758adc658c0aac6a0"
+dependencies = [
+ "cfg-if",
+ "rand",
+ "static_assertions",
+]
+
 [[package]]
 name = "typed-arena"
 version = "2.0.1"

cli/Cargo.toml

@@ -95,6 +95,7 @@ text_lines = "=0.4.1"
 tokio = { version = "=1.17", features = ["full"] }
 tokio-util = "=0.7.0"
 tower-lsp = "=0.16.0"
+twox-hash = "=1.6.2"
 typed-arena = "2.0.1"
 uuid = { version = "=0.8.2", features = ["v4", "serde"] }
 walkdir = "=2.3.2"

cli/config_file.rs

@@ -480,7 +480,7 @@ pub struct LintConfig {
   pub files: FilesConfig,
 }
 
-#[derive(Clone, Copy, Debug, Deserialize)]
+#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
 #[serde(deny_unknown_fields, rename_all = "camelCase")]
 pub enum ProseWrap {
   Always,
@@ -488,7 +488,7 @@ pub enum ProseWrap {
   Preserve,
 }
 
-#[derive(Clone, Debug, Default, Deserialize)]
+#[derive(Clone, Debug, Default, Serialize, Deserialize)]
 #[serde(default, deny_unknown_fields, rename_all = "camelCase")]
 pub struct FmtOptionsConfig {
   pub use_tabs: Option<bool>,

cli/deno_dir.rs

@@ -44,6 +44,18 @@ impl DenoDir {
 
     Ok(deno_dir)
   }
+
+  /// Path for the incremental cache used for formatting.
+  pub fn fmt_incremental_cache_db_file_path(&self) -> PathBuf {
+    // bump this version name to invalidate the entire cache
+    self.root.join("fmt_incremental_cache_v1")
+  }
+
+  /// Path for the incremental cache used for linting.
+  pub fn lint_incremental_cache_db_file_path(&self) -> PathBuf {
+    // bump this version name to invalidate the entire cache
+    self.root.join("lint_incremental_cache_v1")
+  }
 }
 
 /// To avoid the poorly managed dirs crate

cli/lsp/language_server.rs

@@ -1154,7 +1154,7 @@ impl Inner {
         Some(Err(err)) => Err(anyhow!("{}", err)),
         None => {
           // it's not a js/ts file, so attempt to format its contents
-          format_file(&file_path, document.content().as_str(), fmt_options)
+          format_file(&file_path, document.content().as_str(), &fmt_options)
         }
       };
 

cli/main.rs

@@ -908,7 +908,8 @@ async fn format_command(
     return Ok(0);
   }
 
-  tools::fmt::format(ps.flags.as_ref(), fmt_flags, maybe_fmt_config).await?;
+  tools::fmt::format(ps.flags.as_ref(), fmt_flags, maybe_fmt_config, &ps.dir)
+    .await?;
   Ok(0)
 }
 

cli/tools/fmt.rs

@@ -11,6 +11,7 @@ use crate::colors;
 use crate::config_file::FmtConfig;
 use crate::config_file::FmtOptionsConfig;
 use crate::config_file::ProseWrap;
+use crate::deno_dir::DenoDir;
 use crate::diff::diff;
 use crate::file_watcher;
 use crate::file_watcher::ResolutionResult;
@@ -40,11 +41,14 @@ use std::sync::atomic::AtomicUsize;
 use std::sync::atomic::Ordering;
 use std::sync::Arc;
 
+use super::incremental_cache::IncrementalCache;
+
 /// Format JavaScript/TypeScript files.
 pub async fn format(
   flags: &Flags,
   fmt_flags: FmtFlags,
   maybe_fmt_config: Option<FmtConfig>,
+  deno_dir: &DenoDir,
 ) -> Result<(), AnyError> {
   let FmtFlags {
     files,
@@ -132,11 +136,18 @@ pub async fn format(
     }
   };
   let operation = |(paths, fmt_options): (Vec<PathBuf>, FmtOptionsConfig)| async move {
+    let incremental_cache = Arc::new(IncrementalCache::new(
+      &deno_dir.fmt_incremental_cache_db_file_path(),
+      &fmt_options,
+      &paths,
+    ));
     if check {
-      check_source_files(paths, fmt_options).await?;
+      check_source_files(paths, fmt_options, incremental_cache.clone()).await?;
     } else {
-      format_source_files(paths, fmt_options).await?;
+      format_source_files(paths, fmt_options, incremental_cache.clone())
+        .await?;
     }
+    incremental_cache.wait_completion().await;
     Ok(())
   };
 
@@ -234,18 +245,18 @@ pub fn format_json(
 pub fn format_file(
   file_path: &Path,
   file_text: &str,
-  fmt_options: FmtOptionsConfig,
+  fmt_options: &FmtOptionsConfig,
 ) -> Result<Option<String>, AnyError> {
   let ext = get_extension(file_path).unwrap_or_default();
   if matches!(
     ext.as_str(),
     "md" | "mkd" | "mkdn" | "mdwn" | "mdown" | "markdown"
   ) {
-    format_markdown(file_text, &fmt_options)
+    format_markdown(file_text, fmt_options)
   } else if matches!(ext.as_str(), "json" | "jsonc") {
-    format_json(file_text, &fmt_options)
+    format_json(file_text, fmt_options)
   } else {
-    let config = get_resolved_typescript_config(&fmt_options);
+    let config = get_resolved_typescript_config(fmt_options);
     dprint_plugin_typescript::format_text(file_path, file_text, &config)
   }
 }
@@ -263,6 +274,7 @@ pub fn format_parsed_source(
 async fn check_source_files(
   paths: Vec<PathBuf>,
   fmt_options: FmtOptionsConfig,
+  incremental_cache: Arc<IncrementalCache>,
 ) -> Result<(), AnyError> {
   let not_formatted_files_count = Arc::new(AtomicUsize::new(0));
   let checked_files_count = Arc::new(AtomicUsize::new(0));
@@ -277,7 +289,12 @@ async fn check_source_files(
       checked_files_count.fetch_add(1, Ordering::Relaxed);
       let file_text = read_file_contents(&file_path)?.text;
 
-      match format_file(&file_path, &file_text, fmt_options.clone()) {
+      // skip checking the file if we know it's formatted
+      if incremental_cache.is_file_same(&file_path, &file_text) {
+        return Ok(());
+      }
+
+      match format_file(&file_path, &file_text, &fmt_options) {
         Ok(Some(formatted_text)) => {
           not_formatted_files_count.fetch_add(1, Ordering::Relaxed);
           let _g = output_lock.lock();
@@ -286,7 +303,14 @@ async fn check_source_files(
           info!("{} {}:", colors::bold("from"), file_path.display());
           info!("{}", diff);
         }
-        Ok(None) => {}
+        Ok(None) => {
+          // When checking formatting, only update the incremental cache when
+          // the file is the same since we don't bother checking for stable
+          // formatting here. Additionally, ensure this is done during check
+          // so that CIs that cache the DENO_DIR will get the benefit of
+          // incremental formatting
+          incremental_cache.update_file(&file_path, &file_text);
+        }
         Err(e) => {
           let _g = output_lock.lock();
           eprintln!("Error checking: {}", file_path.to_string_lossy());
@@ -318,6 +342,7 @@ async fn check_source_files(
 async fn format_source_files(
   paths: Vec<PathBuf>,
   fmt_options: FmtOptionsConfig,
+  incremental_cache: Arc<IncrementalCache>,
 ) -> Result<(), AnyError> {
   let formatted_files_count = Arc::new(AtomicUsize::new(0));
   let checked_files_count = Arc::new(AtomicUsize::new(0));
@@ -330,8 +355,19 @@ async fn format_source_files(
       checked_files_count.fetch_add(1, Ordering::Relaxed);
       let file_contents = read_file_contents(&file_path)?;
 
-      match format_file(&file_path, &file_contents.text, fmt_options.clone()) {
+      // skip formatting the file if we know it's formatted
+      if incremental_cache.is_file_same(&file_path, &file_contents.text) {
+        return Ok(());
+      }
+
+      match format_ensure_stable(
+        &file_path,
+        &file_contents.text,
+        &fmt_options,
+        format_file,
+      ) {
         Ok(Some(formatted_text)) => {
+          incremental_cache.update_file(&file_path, &formatted_text);
           write_file_contents(
             &file_path,
             FileContents {
@@ -343,7 +379,9 @@ async fn format_source_files(
           let _g = output_lock.lock();
           info!("{}", file_path.to_string_lossy());
         }
-        Ok(None) => {}
+        Ok(None) => {
+          incremental_cache.update_file(&file_path, &file_contents.text);
+        }
         Err(e) => {
           let _g = output_lock.lock();
           eprintln!("Error formatting: {}", file_path.to_string_lossy());
@@ -372,6 +410,66 @@ async fn format_source_files(
   Ok(())
 }
 
+/// When storing any formatted text in the incremental cache, we want
+/// to ensure that anything stored when formatted will have itself as
+/// the output as well. This is to prevent "double format" issues where
+/// a user formats their code locally and it fails on the CI afterwards.
+fn format_ensure_stable(
+  file_path: &Path,
+  file_text: &str,
+  fmt_options: &FmtOptionsConfig,
+  fmt_func: impl Fn(
+    &Path,
+    &str,
+    &FmtOptionsConfig,
+  ) -> Result<Option<String>, AnyError>,
+) -> Result<Option<String>, AnyError> {
+  let formatted_text = fmt_func(file_path, file_text, fmt_options)?;
+
+  match formatted_text {
+    Some(mut current_text) => {
+      let mut count = 0;
+      loop {
+        match fmt_func(file_path, &current_text, fmt_options) {
+          Ok(Some(next_pass_text)) => {
+            // just in case
+            if next_pass_text == current_text {
+              return Ok(Some(next_pass_text));
+            }
+            current_text = next_pass_text;
+          }
+          Ok(None) => {
+            return Ok(Some(current_text));
+          }
+          Err(err) => {
+            panic!(
+              concat!(
+                "Formatting succeeded initially, but failed when ensuring a ",
+                "stable format. This indicates a bug in the formatter where ",
+                "the text it produces is not syntatically correct. As a temporary ",
+                "workfaround you can ignore this file.\n\n{:#}"
+              ),
+              err,
+            )
+          }
+        }
+        count += 1;
+        if count == 5 {
+          panic!(
+            concat!(
+              "Formatting not stable. Bailed after {} tries. This indicates a bug ",
+              "in the formatter where it formats the file differently each time. As a ",
+              "temporary workaround you can ignore this file."
+            ),
+            count
+          )
+        }
+      }
+    }
+    None => Ok(None),
+  }
+}
+
 /// Format stdin and write result to stdout.
 /// Treats input as TypeScript or as set by `--ext` flag.
 /// Compatible with `--check` flag.
@@ -386,7 +484,7 @@ pub fn format_stdin(
   let file_path = PathBuf::from(format!("_stdin.{}", fmt_flags.ext));
   let fmt_options = resolve_fmt_options(&fmt_flags, fmt_options);
 
-  let formatted_text = format_file(&file_path, &source, fmt_options)?;
+  let formatted_text = format_file(&file_path, &source, &fmt_options)?;
   if fmt_flags.check {
     if formatted_text.is_some() {
       println!("Not formatted stdin");
@@ -628,37 +726,106 @@ fn is_contain_git(path: &Path) -> bool {
   path.components().any(|c| c.as_os_str() == ".git")
 }
 
-#[test]
-fn test_is_supported_ext_fmt() {
-  assert!(!is_supported_ext_fmt(Path::new("tests/subdir/redirects")));
-  assert!(is_supported_ext_fmt(Path::new("README.md")));
-  assert!(is_supported_ext_fmt(Path::new("readme.MD")));
-  assert!(is_supported_ext_fmt(Path::new("readme.mkd")));
-  assert!(is_supported_ext_fmt(Path::new("readme.mkdn")));
-  assert!(is_supported_ext_fmt(Path::new("readme.mdwn")));
-  assert!(is_supported_ext_fmt(Path::new("readme.mdown")));
-  assert!(is_supported_ext_fmt(Path::new("readme.markdown")));
-  assert!(is_supported_ext_fmt(Path::new("lib/typescript.d.ts")));
-  assert!(is_supported_ext_fmt(Path::new("testdata/001_hello.js")));
-  assert!(is_supported_ext_fmt(Path::new("testdata/002_hello.ts")));
-  assert!(is_supported_ext_fmt(Path::new("foo.jsx")));
-  assert!(is_supported_ext_fmt(Path::new("foo.tsx")));
-  assert!(is_supported_ext_fmt(Path::new("foo.TS")));
-  assert!(is_supported_ext_fmt(Path::new("foo.TSX")));
-  assert!(is_supported_ext_fmt(Path::new("foo.JS")));
-  assert!(is_supported_ext_fmt(Path::new("foo.JSX")));
-  assert!(is_supported_ext_fmt(Path::new("foo.mjs")));
-  assert!(!is_supported_ext_fmt(Path::new("foo.mjsx")));
-  assert!(is_supported_ext_fmt(Path::new("foo.jsonc")));
-  assert!(is_supported_ext_fmt(Path::new("foo.JSONC")));
-  assert!(is_supported_ext_fmt(Path::new("foo.json")));
-  assert!(is_supported_ext_fmt(Path::new("foo.JsON")));
-}
+#[cfg(test)]
+mod test {
+  use super::*;
 
-#[test]
-fn test_is_located_in_git() {
-  assert!(is_contain_git(Path::new("test/.git")));
-  assert!(is_contain_git(Path::new(".git/bad.json")));
-  assert!(is_contain_git(Path::new("test/.git/bad.json")));
-  assert!(!is_contain_git(Path::new("test/bad.git/bad.json")));
+  #[test]
+  fn test_is_supported_ext_fmt() {
+    assert!(!is_supported_ext_fmt(Path::new("tests/subdir/redirects")));
+    assert!(is_supported_ext_fmt(Path::new("README.md")));
+    assert!(is_supported_ext_fmt(Path::new("readme.MD")));
+    assert!(is_supported_ext_fmt(Path::new("readme.mkd")));
+    assert!(is_supported_ext_fmt(Path::new("readme.mkdn")));
+    assert!(is_supported_ext_fmt(Path::new("readme.mdwn")));
+    assert!(is_supported_ext_fmt(Path::new("readme.mdown")));
+    assert!(is_supported_ext_fmt(Path::new("readme.markdown")));
+    assert!(is_supported_ext_fmt(Path::new("lib/typescript.d.ts")));
+    assert!(is_supported_ext_fmt(Path::new("testdata/001_hello.js")));
+    assert!(is_supported_ext_fmt(Path::new("testdata/002_hello.ts")));
+    assert!(is_supported_ext_fmt(Path::new("foo.jsx")));
+    assert!(is_supported_ext_fmt(Path::new("foo.tsx")));
+    assert!(is_supported_ext_fmt(Path::new("foo.TS")));
+    assert!(is_supported_ext_fmt(Path::new("foo.TSX")));
+    assert!(is_supported_ext_fmt(Path::new("foo.JS")));
+    assert!(is_supported_ext_fmt(Path::new("foo.JSX")));
+    assert!(is_supported_ext_fmt(Path::new("foo.mjs")));
+    assert!(!is_supported_ext_fmt(Path::new("foo.mjsx")));
+    assert!(is_supported_ext_fmt(Path::new("foo.jsonc")));
+    assert!(is_supported_ext_fmt(Path::new("foo.JSONC")));
+    assert!(is_supported_ext_fmt(Path::new("foo.json")));
+    assert!(is_supported_ext_fmt(Path::new("foo.JsON")));
+  }
+
+  #[test]
+  fn test_is_located_in_git() {
+    assert!(is_contain_git(Path::new("test/.git")));
+    assert!(is_contain_git(Path::new(".git/bad.json")));
+    assert!(is_contain_git(Path::new("test/.git/bad.json")));
+    assert!(!is_contain_git(Path::new("test/bad.git/bad.json")));
+  }
+
+  #[test]
+  #[should_panic(expected = "Formatting not stable. Bailed after 5 tries.")]
+  fn test_format_ensure_stable_unstable_format() {
+    format_ensure_stable(
+      &PathBuf::from("mod.ts"),
+      "1",
+      &Default::default(),
+      |_, file_text, _| Ok(Some(format!("1{}", file_text))),
+    )
+    .unwrap();
+  }
+
+  #[test]
+  fn test_format_ensure_stable_error_first() {
+    let err = format_ensure_stable(
+      &PathBuf::from("mod.ts"),
+      "1",
+      &Default::default(),
+      |_, _, _| bail!("Error formatting."),
+    )
+    .unwrap_err();
+
+    assert_eq!(err.to_string(), "Error formatting.");
+  }
+
+  #[test]
+  #[should_panic(expected = "Formatting succeeded initially, but failed when")]
+  fn test_format_ensure_stable_error_second() {
+    format_ensure_stable(
+      &PathBuf::from("mod.ts"),
+      "1",
+      &Default::default(),
+      |_, file_text, _| {
+        if file_text == "1" {
+          Ok(Some("11".to_string()))
+        } else {
+          bail!("Error formatting.")
+        }
+      },
+    )
+    .unwrap();
+  }
+
+  #[test]
+  fn test_format_stable_after_two() {
+    let result = format_ensure_stable(
+      &PathBuf::from("mod.ts"),
+      "1",
+      &Default::default(),
+      |_, file_text, _| {
+        if file_text == "1" {
+          Ok(Some("11".to_string()))
+        } else if file_text == "11" {
+          Ok(None)
+        } else {
+          unreachable!();
+        }
+      },
+    )
+    .unwrap();
+
+    assert_eq!(result, Some("11".to_string()));
+  }
 }

cli/tools/incremental_cache.rs

@@ -0,0 +1,371 @@
+use std::collections::HashMap;
+use std::path::Path;
+use std::path::PathBuf;
+
+use deno_core::error::AnyError;
+use deno_core::parking_lot::Mutex;
+use deno_core::serde_json;
+use deno_runtime::deno_webstorage::rusqlite::params;
+use deno_runtime::deno_webstorage::rusqlite::Connection;
+use serde::Serialize;
+use tokio::task::JoinHandle;
+
+/// Cache used to skip formatting/linting a file again when we
+/// know it is already formatted or has no lint diagnostics.
+pub struct IncrementalCache(Option<IncrementalCacheInner>);
+
+impl IncrementalCache {
+  pub fn new<TState: Serialize>(
+    db_file_path: &Path,
+    state: &TState,
+    initial_file_paths: &[PathBuf],
+  ) -> Self {
+    // if creating the incremental cache fails, then we
+    // treat it as not having a cache
+    let result =
+      IncrementalCacheInner::new(db_file_path, state, initial_file_paths);
+    IncrementalCache(match result {
+      Ok(inner) => Some(inner),
+      Err(err) => {
+        log::debug!("Creating the incremental cache failed.\n{:#}", err);
+        // Maybe the cache file is corrupt. Attempt to remove
+        // the cache file for next time
+        let _ = std::fs::remove_file(db_file_path);
+        None
+      }
+    })
+  }
+
+  pub fn is_file_same(&self, file_path: &Path, file_text: &str) -> bool {
+    if let Some(inner) = &self.0 {
+      inner.is_file_same(file_path, file_text)
+    } else {
+      false
+    }
+  }
+
+  pub fn update_file(&self, file_path: &Path, file_text: &str) {
+    if let Some(inner) = &self.0 {
+      inner.update_file(file_path, file_text)
+    }
+  }
+
+  pub async fn wait_completion(&self) {
+    if let Some(inner) = &self.0 {
+      inner.wait_completion().await;
+    }
+  }
+}
+
+enum ReceiverMessage {
+  Update(PathBuf, u64),
+  Exit,
+}
+
+struct IncrementalCacheInner {
+  previous_hashes: HashMap<PathBuf, u64>,
+  sender: tokio::sync::mpsc::UnboundedSender<ReceiverMessage>,
+  handle: Mutex<Option<JoinHandle<()>>>,
+}
+
+impl IncrementalCacheInner {
+  pub fn new<TState: Serialize>(
+    db_file_path: &Path,
+    state: &TState,
+    initial_file_paths: &[PathBuf],
+  ) -> Result<Self, AnyError> {
+    let state_hash =
+      fast_insecure_hash(serde_json::to_string(state).unwrap().as_bytes());
+    let sql_cache = SqlIncrementalCache::new(db_file_path, state_hash)?;
+    Ok(Self::from_sql_incremental_cache(
+      sql_cache,
+      initial_file_paths,
+    ))
+  }
+
+  fn from_sql_incremental_cache(
+    cache: SqlIncrementalCache,
+    initial_file_paths: &[PathBuf],
+  ) -> Self {
+    let mut previous_hashes = HashMap::new();
+    for path in initial_file_paths {
+      if let Some(hash) = cache.get_source_hash(path) {
+        previous_hashes.insert(path.to_path_buf(), hash);
+      }
+    }
+
+    let (sender, mut receiver) =
+      tokio::sync::mpsc::unbounded_channel::<ReceiverMessage>();
+
+    // sqlite isn't `Sync`, so we do all the updating on a dedicated task
+    let handle = tokio::task::spawn(async move {
+      while let Some(message) = receiver.recv().await {
+        match message {
+          ReceiverMessage::Update(path, hash) => {
+            let _ = cache.set_source_hash(&path, hash);
+          }
+          ReceiverMessage::Exit => break,
+        }
+      }
+    });
+
+    IncrementalCacheInner {
+      previous_hashes,
+      sender,
+      handle: Mutex::new(Some(handle)),
+    }
+  }
+
+  pub fn is_file_same(&self, file_path: &Path, file_text: &str) -> bool {
+    match self.previous_hashes.get(file_path) {
+      Some(hash) => *hash == fast_insecure_hash(file_text.as_bytes()),
+      None => false,
+    }
+  }
+
+  pub fn update_file(&self, file_path: &Path, file_text: &str) {
+    let hash = fast_insecure_hash(file_text.as_bytes());
+    if let Some(previous_hash) = self.previous_hashes.get(file_path) {
+      if *previous_hash == hash {
+        return; // do not bother updating the db file because nothing has changed
+      }
+    }
+    let _ = self
+      .sender
+      .send(ReceiverMessage::Update(file_path.to_path_buf(), hash));
+  }
+
+  pub async fn wait_completion(&self) {
+    if self.sender.send(ReceiverMessage::Exit).is_err() {
+      return;
+    }
+    let handle = self.handle.lock().take();
+    if let Some(handle) = handle {
+      handle.await.unwrap();
+    }
+  }
+}
+
+struct SqlIncrementalCache {
+  conn: Connection,
+  /// A hash of the state used to produce the formatting/linting other than
+  /// the CLI version. This state is a hash of the configuration and ensures
+  /// we format/lint a file when the configuration changes.
+  state_hash: u64,
+}
+
+impl SqlIncrementalCache {
+  pub fn new(db_file_path: &Path, state_hash: u64) -> Result<Self, AnyError> {
+    let conn = Connection::open(db_file_path)?;
+    Self::from_connection(conn, state_hash, crate::version::deno())
+  }
+
+  fn from_connection(
+    conn: Connection,
+    state_hash: u64,
+    cli_version: String,
+  ) -> Result<Self, AnyError> {
+    run_pragma(&conn)?;
+    create_tables(&conn, cli_version)?;
+
+    Ok(Self { conn, state_hash })
+  }
+
+  pub fn get_source_hash(&self, path: &Path) -> Option<u64> {
+    match self.get_source_hash_result(path) {
+      Ok(option) => option,
+      Err(err) => {
+        if cfg!(debug_assertions) {
+          panic!("Error retrieving hash: {}", err);
+        } else {
+          // fail silently when not debugging
+          None
+        }
+      }
+    }
+  }
+
+  fn get_source_hash_result(
+    &self,
+    path: &Path,
+  ) -> Result<Option<u64>, AnyError> {
+    let query = "
+      SELECT
+        source_hash
+      FROM
+        incrementalcache
+      WHERE
+        file_path=?1
+        AND state_hash=?2
+      LIMIT 1";
+    let mut stmt = self.conn.prepare_cached(query)?;
+    let mut rows = stmt
+      .query(params![path.to_string_lossy(), self.state_hash.to_string()])?;
+    if let Some(row) = rows.next()? {
+      let hash: String = row.get(0)?;
+      Ok(Some(hash.parse::<u64>()?))
+    } else {
+      Ok(None)
+    }
+  }
+
+  pub fn set_source_hash(
+    &self,
+    path: &Path,
+    source_hash: u64,
+  ) -> Result<(), AnyError> {
+    let sql = "
+      INSERT OR REPLACE INTO
+        incrementalcache (file_path, state_hash, source_hash)
+      VALUES
+        (?1, ?2, ?3)";
+    let mut stmt = self.conn.prepare_cached(sql)?;
+    stmt.execute(params![
+      path.to_string_lossy(),
+      &self.state_hash.to_string(),
+      &source_hash.to_string(),
+    ])?;
+    Ok(())
+  }
+}
+
+fn run_pragma(conn: &Connection) -> Result<(), AnyError> {
+  // Enable write-ahead-logging and tweak some other stuff
+  let initial_pragmas = "
+    -- enable write-ahead-logging mode
+    PRAGMA journal_mode=WAL;
+    PRAGMA synchronous=NORMAL;
+    PRAGMA temp_store=memory;
+    PRAGMA page_size=4096;
+    PRAGMA mmap_size=6000000;
+    PRAGMA optimize;
+  ";
+
+  conn.execute_batch(initial_pragmas)?;
+  Ok(())
+}
+
+fn create_tables(
+  conn: &Connection,
+  cli_version: String,
+) -> Result<(), AnyError> {
+  // INT doesn't store up to u64, so use TEXT
+  conn.execute(
+    "CREATE TABLE IF NOT EXISTS incrementalcache (
+        file_path TEXT PRIMARY KEY,
+        state_hash TEXT NOT NULL,
+        source_hash TEXT NOT NULL
+      )",
+    [],
+  )?;
+  conn.execute(
+    "CREATE TABLE IF NOT EXISTS info (
+        key TEXT PRIMARY KEY,
+        value TEXT NOT NULL
+      )",
+    [],
+  )?;
+
+  // delete the cache when the CLI version changes
+  let data_cli_version: Option<String> = conn
+    .query_row(
+      "SELECT value FROM info WHERE key='CLI_VERSION' LIMIT 1",
+      [],
+      |row| row.get(0),
+    )
+    .ok();
+  if data_cli_version != Some(cli_version.to_string()) {
+    conn.execute("DELETE FROM incrementalcache", params![])?;
+    let mut stmt = conn
+      .prepare("INSERT OR REPLACE INTO info (key, value) VALUES (?1, ?2)")?;
+    stmt.execute(params!["CLI_VERSION", &cli_version])?;
+  }
+
+  Ok(())
+}
+
+/// Very fast non-cryptographically secure hash.
+fn fast_insecure_hash(bytes: &[u8]) -> u64 {
+  use std::hash::Hasher;
+  use twox_hash::XxHash64;
+
+  let mut hasher = XxHash64::default();
+  hasher.write(bytes);
+  hasher.finish()
+}
+
+#[cfg(test)]
+mod test {
+  use std::path::PathBuf;
+
+  use super::*;
+
+  #[test]
+  pub fn sql_cache_general_use() {
+    let conn = Connection::open_in_memory().unwrap();
+    let cache =
+      SqlIncrementalCache::from_connection(conn, 1, "1.0.0".to_string())
+        .unwrap();
+    let path = PathBuf::from("/mod.ts");
+
+    assert_eq!(cache.get_source_hash(&path), None);
+    cache.set_source_hash(&path, 2).unwrap();
+    assert_eq!(cache.get_source_hash(&path), Some(2));
+
+    // try changing the cli version (should clear)
+    let conn = cache.conn;
+    let mut cache =
+      SqlIncrementalCache::from_connection(conn, 1, "2.0.0".to_string())
+        .unwrap();
+    assert_eq!(cache.get_source_hash(&path), None);
+
+    // add back the file to the cache
+    cache.set_source_hash(&path, 2).unwrap();
+    assert_eq!(cache.get_source_hash(&path), Some(2));
+
+    // try changing the state hash
+    cache.state_hash = 2;
+    assert_eq!(cache.get_source_hash(&path), None);
+    cache.state_hash = 1;
+
+    // should return now that everything is back
+    assert_eq!(cache.get_source_hash(&path), Some(2));
+
+    // recreating the cache should not remove the data because the CLI version and state hash is the same
+    let conn = cache.conn;
+    let cache =
+      SqlIncrementalCache::from_connection(conn, 1, "2.0.0".to_string())
+        .unwrap();
+    assert_eq!(cache.get_source_hash(&path), Some(2));
+
+    // now try replacing and using another path
+    cache.set_source_hash(&path, 3).unwrap();
+    cache.set_source_hash(&path, 4).unwrap();
+    let path2 = PathBuf::from("/mod2.ts");
+    cache.set_source_hash(&path2, 5).unwrap();
+    assert_eq!(cache.get_source_hash(&path), Some(4));
+    assert_eq!(cache.get_source_hash(&path2), Some(5));
+  }
+
+  #[tokio::test]
+  pub async fn incremental_cache_general_use() {
+    let conn = Connection::open_in_memory().unwrap();
+    let sql_cache =
+      SqlIncrementalCache::from_connection(conn, 1, "1.0.0".to_string())
+        .unwrap();
+    let file_path = PathBuf::from("/mod.ts");
+    let file_text = "test";
+    let file_hash = fast_insecure_hash(file_text.as_bytes());
+    sql_cache.set_source_hash(&file_path, file_hash).unwrap();
+    let cache = IncrementalCacheInner::from_sql_incremental_cache(
+      sql_cache,
+      &[file_path.clone()],
+    );
+
+    assert!(cache.is_file_same(&file_path, "test"));
+    assert!(!cache.is_file_same(&file_path, "other"));
+
+    // just ensure this doesn't panic
+    cache.update_file(&file_path, "other");
+  }
+}

cli/tools/lint.rs

@@ -34,6 +34,8 @@ use std::path::PathBuf;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Mutex};
 
+use super::incremental_cache::IncrementalCache;
+
 static STDIN_FILE_NAME: &str = "_stdin.ts";
 
 #[derive(Clone, Debug)]
@@ -147,6 +149,17 @@ pub async fn lint(flags: Flags, lint_flags: LintFlags) -> Result<(), AnyError> {
   };
 
   let operation = |paths: Vec<PathBuf>| async {
+    let incremental_cache = Arc::new(IncrementalCache::new(
+      &ps.dir.lint_incremental_cache_db_file_path(),
+      // use a hash of the rule names in order to bust the cache
+      &{
+        // ensure this is stable by sorting it
+        let mut names = lint_rules.iter().map(|r| r.code()).collect::<Vec<_>>();
+        names.sort_unstable();
+        names
+      },
+      &paths,
+    ));
     let target_files_len = paths.len();
     let reporter_kind = reporter_kind.clone();
     let reporter_lock = Arc::new(Mutex::new(create_reporter(reporter_kind)));
@@ -154,8 +167,23 @@ pub async fn lint(flags: Flags, lint_flags: LintFlags) -> Result<(), AnyError> {
       let has_error = has_error.clone();
       let lint_rules = lint_rules.clone();
       let reporter_lock = reporter_lock.clone();
+      let incremental_cache = incremental_cache.clone();
       move |file_path| {
-        let r = lint_file(file_path.clone(), lint_rules.clone());
+        let file_text = fs::read_to_string(&file_path)?;
+
+        // don't bother rechecking this file if it didn't have any diagnostics before
+        if incremental_cache.is_file_same(&file_path, &file_text) {
+          return Ok(());
+        }
+
+        let r = lint_file(file_path.clone(), file_text, lint_rules.clone());
+        if let Ok((file_diagnostics, file_text)) = &r {
+          if file_diagnostics.is_empty() {
+            // update the incremental cache if there were no diagnostics
+            incremental_cache.update_file(&file_path, file_text)
+          }
+        }
+
         handle_lint_result(
           &file_path.to_string_lossy(),
           r,
@@ -167,6 +195,7 @@ pub async fn lint(flags: Flags, lint_flags: LintFlags) -> Result<(), AnyError> {
       }
     })
     .await?;
+    incremental_cache.wait_completion().await;
     reporter_lock.lock().unwrap().close(target_files_len);
 
     Ok(())
@@ -262,10 +291,10 @@ pub fn create_linter(
 
 fn lint_file(
   file_path: PathBuf,
+  source_code: String,
   lint_rules: Vec<Arc<dyn LintRule>>,
 ) -> Result<(Vec<LintDiagnostic>, String), AnyError> {
   let file_name = file_path.to_string_lossy().to_string();
-  let source_code = fs::read_to_string(&file_path)?;
   let media_type = MediaType::from(&file_path);
 
   let linter = create_linter(media_type, lint_rules);

cli/tools/mod.rs

@@ -4,6 +4,7 @@ pub mod bench;
 pub mod coverage;
 pub mod doc;
 pub mod fmt;
+pub mod incremental_cache;
 pub mod installer;
 pub mod lint;
 pub mod repl;

ext/webstorage/lib.rs

@@ -13,6 +13,8 @@ use rusqlite::OptionalExtension;
 use std::fmt;
 use std::path::PathBuf;
 
+pub use rusqlite;
+
 #[derive(Clone)]
 struct OriginStorageDir(PathBuf);