diff --git a/clippy_dev/Cargo.toml b/clippy_dev/Cargo.toml
index f48c1ee5ea2..5ac96e2210c 100644
--- a/clippy_dev/Cargo.toml
+++ b/clippy_dev/Cargo.toml
@@ -9,6 +9,7 @@ edition = "2018"
 bytecount = "0.6"
 clap = "2.33"
 flate2 = { version = "1.0.19", optional = true }
+fs_extra = { version = "1.2.0", optional = true }
 itertools = "0.9"
 opener = "0.4"
 regex = "1"
@@ -21,5 +22,5 @@ ureq = { version = "2.0.0-rc3", optional = true }
 walkdir = "2"
 
 [features]
-lintcheck = ["flate2", "serde_json", "tar", "toml", "ureq", "serde"]
+lintcheck = ["flate2", "serde_json", "tar", "toml", "ureq", "serde", "fs_extra"]
 deny-warnings = []
diff --git a/clippy_dev/README.md b/clippy_dev/README.md
new file mode 100644
index 00000000000..3846e8bd4cc
--- /dev/null
+++ b/clippy_dev/README.md
@@ -0,0 +1,28 @@
+# Clippy Dev Tool 
+
+The Clippy Dev Tool is a tool to ease Clippy development, similar to `rustc`s `x.py`.
+
+Functionalities (incomplete):
+
+## `lintcheck`
+Runs clippy on a fixed set of crates read from `clippy_dev/lintcheck_crates.toml`
+and saves logs of the lint warnings into the repo.
+We can then check the diff and spot new or disappearing warnings.
+
+From the repo root, run:
+````
+cargo run --target-dir clippy_dev/target --package clippy_dev \
+--bin clippy_dev --manifest-path clippy_dev/Cargo.toml --features lintcheck -- lintcheck
+````
+or
+````
+cargo dev-lintcheck
+````
+
+By default the logs will be saved into `lintcheck-logs/lintcheck_crates_logs.txt`.
+
+You can set a custom sources.toml by adding `--crates-toml custom.toml`
+where `custom.toml` must be a relative path from the repo root.
+
+The results will then be saved to `lintcheck-logs/custom_logs.toml`.
+
diff --git a/clippy_dev/lintcheck_crates.toml b/clippy_dev/lintcheck_crates.toml
index c83b4b2ba42..60e70ca4eb2 100644
--- a/clippy_dev/lintcheck_crates.toml
+++ b/clippy_dev/lintcheck_crates.toml
@@ -4,11 +4,13 @@ cargo = {name = "cargo", versions = ['0.49.0']}
 iron = {name = "iron", versions = ['0.6.1']}
 ripgrep = {name = "ripgrep", versions = ['12.1.1']}
 xsv = {name = "xsv", versions = ['0.13.0']}
+# commented out because of 173K clippy::match_same_arms msgs in language_type.rs
 #tokei = { name = "tokei", versions = ['12.0.4']}
 rayon = {name = "rayon", versions = ['1.5.0']}
 serde = {name = "serde", versions = ['1.0.118']}
 # top 10 crates.io dls
 bitflags = {name = "bitflags", versions = ['1.2.1']}
+# crash = {name = "clippy_crash", path = "/tmp/clippy_crash"}
 libc = {name = "libc", versions = ['0.2.81']}
 log = {name = "log", versions = ['0.4.11']}
 proc-macro2 = {name = "proc-macro2", versions = ['1.0.24']}
diff --git a/clippy_dev/src/lintcheck.rs b/clippy_dev/src/lintcheck.rs
index 3fc7dcb7d4b..749a791b280 100644
--- a/clippy_dev/src/lintcheck.rs
+++ b/clippy_dev/src/lintcheck.rs
@@ -31,13 +31,15 @@ struct TomlCrate {
     versions: Option<Vec<String>>,
     git_url: Option<String>,
     git_hash: Option<String>,
+    path: Option<String>,
 }
 
-// represents an archive we download from crates.io
+// represents an archive we download from crates.io, or a git repo, or a local repo
 #[derive(Debug, Serialize, Deserialize, Eq, Hash, PartialEq)]
 enum CrateSource {
     CratesIo { name: String, version: String },
     Git { name: String, url: String, commit: String },
+    Path { name: String, path: PathBuf },
 }
 
 // represents the extracted sourcecode of a crate
@@ -60,6 +62,7 @@ struct ClippyWarning {
     column: String,
     linttype: String,
     message: String,
+    ice: bool,
 }
 
 impl std::fmt::Display for ClippyWarning {
@@ -111,7 +114,7 @@ impl CrateSource {
             },
             CrateSource::Git { name, url, commit } => {
                 let repo_path = {
-                    let mut repo_path = PathBuf::from("target/lintcheck/downloads");
+                    let mut repo_path = PathBuf::from("target/lintcheck/crates");
                     // add a -git suffix in case we have the same crate from crates.io and a git repo
                     repo_path.push(format!("{}-git", name));
                     repo_path
@@ -139,6 +142,37 @@ impl CrateSource {
                     path: repo_path,
                 }
             },
+            CrateSource::Path { name, path } => {
+                use fs_extra::dir;
+
+                // simply copy the entire directory into our target dir
+                let copy_dest = PathBuf::from("target/lintcheck/crates/");
+
+                // the source path of the crate we copied,  ${copy_dest}/crate_name
+                let crate_root = copy_dest.join(name); // .../crates/local_crate
+
+                if !crate_root.exists() {
+                    println!("Copying {} to {}", path.display(), copy_dest.display());
+
+                    dir::copy(path, &copy_dest, &dir::CopyOptions::new()).expect(&format!(
+                        "Failed to copy from {}, to  {}",
+                        path.display(),
+                        crate_root.display()
+                    ));
+                } else {
+                    println!(
+                        "Not copying {} to {}, destination already exists",
+                        path.display(),
+                        crate_root.display()
+                    );
+                }
+
+                Crate {
+                    version: String::from("local"),
+                    name: name.clone(),
+                    path: crate_root,
+                }
+            },
         }
     }
 }
@@ -176,8 +210,8 @@ impl Crate {
         let output_lines = stdout.lines();
         let warnings: Vec<ClippyWarning> = output_lines
             .into_iter()
-            // get all clippy warnings
-            .filter(|line| line.contains("clippy::"))
+            // get all clippy warnings and ICEs
+            .filter(|line| line.contains("clippy::") || line.contains("internal compiler error: "))
             .map(|json_msg| parse_json_message(json_msg, &self))
             .collect();
         warnings
@@ -192,8 +226,10 @@ fn build_clippy() {
 }
 
 // get a list of CrateSources we want to check from a "lintcheck_crates.toml" file.
-fn read_crates(toml_path: Option<&str>) -> Vec<CrateSource> {
+fn read_crates(toml_path: Option<&str>) -> (String, Vec<CrateSource>) {
     let toml_path = PathBuf::from(toml_path.unwrap_or("clippy_dev/lintcheck_crates.toml"));
+    // save it so that we can use the name of the sources.toml as name for the logfile later.
+    let toml_filename = toml_path.file_stem().unwrap().to_str().unwrap().to_string();
     let toml_content: String =
         std::fs::read_to_string(&toml_path).unwrap_or_else(|_| panic!("Failed to read {}", toml_path.display()));
     let crate_list: CrateList =
@@ -209,6 +245,13 @@ fn read_crates(toml_path: Option<&str>) -> Vec<CrateSource> {
     // multiple Cratesources)
     let mut crate_sources = Vec::new();
     tomlcrates.into_iter().for_each(|tk| {
+        if let Some(ref path) = tk.path {
+            crate_sources.push(CrateSource::Path {
+                name: tk.name.clone(),
+                path: PathBuf::from(path),
+            });
+        }
+
         // if we have multiple versions, save each one
         if let Some(ref versions) = tk.versions {
             versions.iter().for_each(|ver| {
@@ -232,12 +275,15 @@ fn read_crates(toml_path: Option<&str>) -> Vec<CrateSource> {
         {
             eprintln!("tomlkrate: {:?}", tk);
             if tk.git_hash.is_some() != tk.git_url.is_some() {
-                panic!("Encountered TomlCrate with only one of git_hash and git_url!")
+                panic!("Error: Encountered TomlCrate with only one of git_hash and git_url!");
+            }
+            if tk.path.is_some() && (tk.git_hash.is_some() || tk.versions.is_some()) {
+                panic!("Error: TomlCrate can only have one of 'git_.*', 'version' or 'path' fields");
             }
             unreachable!("Failed to translate TomlCrate into CrateSource!");
         }
     });
-    crate_sources
+    (toml_filename, crate_sources)
 }
 
 // extract interesting data from a json lint message
@@ -261,6 +307,7 @@ fn parse_json_message(json_message: &str, krate: &Crate) -> ClippyWarning {
             .into(),
         linttype: jmsg["message"]["code"]["code"].to_string().trim_matches('"').into(),
         message: jmsg["message"]["message"].to_string().trim_matches('"').into(),
+        ice: json_message.contains("internal compiler error: "),
     }
 }
 
@@ -288,7 +335,7 @@ pub fn run(clap_config: &ArgMatches) {
     // download and extract the crates, then run clippy on them and collect clippys warnings
     // flatten into one big list of warnings
 
-    let crates = read_crates(clap_config.value_of("crates-toml"));
+    let (filename, crates) = read_crates(clap_config.value_of("crates-toml"));
 
     let clippy_warnings: Vec<ClippyWarning> = if let Some(only_one_crate) = clap_config.value_of("only") {
         // if we don't have the specified crate in the .toml, throw an error
@@ -296,6 +343,7 @@ pub fn run(clap_config: &ArgMatches) {
             let name = match krate {
                 CrateSource::CratesIo { name, .. } => name,
                 CrateSource::Git { name, .. } => name,
+                CrateSource::Path { name, .. } => name,
             };
             name == only_one_crate
         }) {
@@ -326,6 +374,13 @@ pub fn run(clap_config: &ArgMatches) {
 
     // generate some stats:
 
+    // grab crashes/ICEs, save the crate name and the ice message
+    let ices: Vec<(&String, &String)> = clippy_warnings
+        .iter()
+        .filter(|warning| warning.ice)
+        .map(|w| (&w.crate_name, &w.message))
+        .collect();
+
     // count lint type occurrences
     let mut counter: HashMap<&String, usize> = HashMap::new();
     clippy_warnings
@@ -351,5 +406,10 @@ pub fn run(clap_config: &ArgMatches) {
     // save the text into lintcheck-logs/logs.txt
     let mut text = clippy_ver; // clippy version number on top
     text.push_str(&format!("\n{}", all_msgs.join("")));
-    write("lintcheck-logs/logs.txt", text).unwrap();
+    text.push_str("ICEs:\n");
+    ices.iter()
+        .for_each(|(cratename, msg)| text.push_str(&format!("{}: '{}'", cratename, msg)));
+
+    let file = format!("lintcheck-logs/{}_logs.txt", filename);
+    write(file, text).unwrap();
 }
diff --git a/lintcheck-logs/logs.txt b/lintcheck-logs/lintcheck_crates_logs.txt
similarity index 100%
rename from lintcheck-logs/logs.txt
rename to lintcheck-logs/lintcheck_crates_logs.txt