fix(deno_dir): better error message (#5120)

Add better error messages when a cache subdirectory in 
`DENO_DIR` cannot be created.

cli/deno_dir.rs

@@ -31,6 +31,7 @@ impl DenoDir {
       root,
       gen_cache: DiskCache::new(&gen_path),
     };
+    deno_dir.gen_cache.ensure_location()?;
 
     Ok(deno_dir)
   }

cli/disk_cache.rs

@@ -1,6 +1,7 @@
 use crate::fs as deno_fs;
 use std::ffi::OsStr;
 use std::fs;
+use std::io;
 use std::path::Component;
 use std::path::Path;
 use std::path::PathBuf;
@@ -22,14 +23,24 @@ fn with_io_context<T: AsRef<str>>(
 
 impl DiskCache {
   pub fn new(location: &Path) -> Self {
-    if !&location.is_dir() {
-      fs::create_dir_all(&location).ok();
-    }
     Self {
       location: location.to_owned(),
     }
   }
 
+  /// Ensures the location of the cache.
+  pub fn ensure_location(&self) -> io::Result<()> {
+    if self.location.is_dir() {
+      return Ok(());
+    }
+    fs::create_dir_all(&self.location).map_err(|e| {
+      io::Error::new(e.kind(), format!(
+        "Could not create TypeScript compiler cache location: {:?}\nCheck the permission of the directory.",
+        self.location
+      ))
+    })
+  }
+
   pub fn get_cache_filename(&self, url: &Url) -> PathBuf {
     let mut out = PathBuf::new();
 
@@ -140,7 +151,8 @@ mod tests {
     let cache_location = TempDir::new().unwrap();
     let mut cache_path = cache_location.path().to_owned();
     cache_path.push("foo");
-    DiskCache::new(&cache_path);
+    let cache = DiskCache::new(&cache_path);
+    cache.ensure_location().expect("Testing expect:");
     assert!(cache_path.is_dir());
   }
 
@@ -151,7 +163,8 @@ mod tests {
     assert!(fs::remove_dir(&cache_location).is_ok());
     cache_location.push("foo");
     assert_eq!(cache_location.is_dir(), false);
-    DiskCache::new(&cache_location);
+    let cache = DiskCache::new(&cache_location);
+    cache.ensure_location().expect("Testing expect:");
     assert_eq!(cache_location.is_dir(), true);
   }
 

cli/file_fetcher.rs

@@ -661,7 +661,7 @@ mod tests {
 
   fn setup_file_fetcher(dir_path: &Path) -> SourceFileFetcher {
     SourceFileFetcher::new(
-      HttpCache::new(&dir_path.to_path_buf().join("deps")).unwrap(),
+      HttpCache::new(&dir_path.to_path_buf().join("deps")),
       true,
       vec![],
       false,

cli/global_state.rs

@@ -54,7 +54,8 @@ impl GlobalState {
     let custom_root = env::var("DENO_DIR").map(String::into).ok();
     let dir = deno_dir::DenoDir::new(custom_root)?;
     let deps_cache_location = dir.root.join("deps");
-    let http_cache = http_cache::HttpCache::new(&deps_cache_location)?;
+    let http_cache = http_cache::HttpCache::new(&deps_cache_location);
+    http_cache.ensure_location()?;
 
     let file_fetcher = SourceFileFetcher::new(
       http_cache,

cli/http_cache.rs

@@ -11,6 +11,7 @@ use serde::Serialize;
 use serde_derive::Deserialize;
 use std::fs;
 use std::fs::File;
+use std::io;
 use std::path::Path;
 use std::path::PathBuf;
 use url::Url;
@@ -101,12 +102,26 @@ impl Metadata {
 }
 
 impl HttpCache {
-  /// Returns error if unable to create directory
-  /// at specified location.
-  pub fn new(location: &Path) -> Result<Self, ErrBox> {
-    fs::create_dir_all(&location)?;
-    Ok(Self {
+  /// Returns a new instance.
+  pub fn new(location: &Path) -> Self {
+    Self {
       location: location.to_owned(),
+    }
+  }
+
+  /// Ensures the location of the cache.
+  pub fn ensure_location(&self) -> io::Result<()> {
+    if self.location.is_dir() {
+      return Ok(());
+    }
+    fs::create_dir_all(&self.location).map_err(|e| {
+      io::Error::new(
+        e.kind(),
+        format!(
+          "Could not create remote modules cache location: {:?}\nCheck the permission of the directory.",
+          self.location
+        ),
+      )
     })
   }
 
@@ -169,15 +184,15 @@ mod tests {
     let dir = TempDir::new().unwrap();
     let mut cache_path = dir.path().to_owned();
     cache_path.push("foobar");
-    let r = HttpCache::new(&cache_path);
-    assert!(r.is_ok());
+    let cache = HttpCache::new(&cache_path);
+    assert!(cache.ensure_location().is_ok());
     assert!(cache_path.is_dir());
   }
 
   #[test]
   fn test_get_set() {
     let dir = TempDir::new().unwrap();
-    let cache = HttpCache::new(dir.path()).unwrap();
+    let cache = HttpCache::new(dir.path());
     let url = Url::parse("https://deno.land/x/welcome.ts").unwrap();
     let mut headers = HashMap::new();
     headers.insert(