Fix cache-entry remove on Windows. (#106)

Author: floitsch

src/cache.toit

@@ -76,9 +76,15 @@ class Cache:
     if file.is-file key-path:
       file.delete key-path
     else if file.is-directory key-path:
-      tmp-path := directory.mkdtemp key-path
-      file.rename key-path tmp-path
-      directory.rmdir --recursive --force tmp-path
+      // Move the entry into a freshly created temp directory so concurrent
+      //   readers see the entry either fully present or gone. We rename it
+      //   *into* the temp dir (rather than *over* it) so the destination
+      //   child path is guaranteed not to exist: this works on Windows,
+      //   where 'rename' cannot overwrite an existing directory, and avoids
+      //   a race window with any sibling using the same temp name.
+      tmp-dir := directory.mkdtemp key-path
+      file.rename key-path (fs.join tmp-dir "entry")
+      directory.rmdir --recursive --force tmp-dir
 
   /**
   Whether the cache contains the given $key.

tests/cache_test.toit

@@ -11,6 +11,7 @@ import expect show *
 main:
   test-file-cache
   test-dir-cache
+  test-remove
 
 test-file-cache:
   cache-dir := directory.mkdtemp "/tmp/cache_test-"
@@ -326,3 +327,49 @@ test-dir-cache:
 
   finally:
     directory.rmdir --recursive cache-dir
+
+test-remove:
+  cache-dir := directory.mkdtemp "/tmp/cache_test-"
+  try:
+    c := cache.Cache --app-name="test" --path=cache-dir
+
+    // Removing a non-existing entry is a no-op.
+    c.remove "missing"
+
+    // Remove a file entry.
+    file-key := "file-key"
+    c.get file-key: | store/cache.FileStore | store.save #[1, 2, 3]
+    expect (c.contains file-key)
+    c.remove file-key
+    expect-not (c.contains file-key)
+
+    // Remove a directory entry.
+    dir-key := "dir-key"
+    c.get-directory-path dir-key: | store/cache.DirectoryStore |
+      store.with-tmp-directory: | dir |
+        write-content --path="$dir/file" --content=#[4, 5, 6]
+        store.move dir
+    expect (c.contains dir-key)
+    c.remove dir-key
+    expect-not (c.contains dir-key)
+
+    // Remove a nested directory entry, then recreate it.
+    nested-key := "nested/dir-key"
+    c.get-directory-path nested-key: | store/cache.DirectoryStore |
+      store.with-tmp-directory: | dir |
+        write-content --path="$dir/file" --content=#[7, 8, 9]
+        store.move dir
+    expect (c.contains nested-key)
+    c.remove nested-key
+    expect-not (c.contains nested-key)
+
+    c.get-directory-path nested-key: | store/cache.DirectoryStore |
+      store.with-tmp-directory: | dir |
+        write-content --path="$dir/file" --content=#[10, 11, 12]
+        store.move dir
+    expect (c.contains nested-key)
+    nested-path := c.get-directory-path nested-key
+    expect-equals #[10, 11, 12] (file.read-contents "$nested-path/file")
+
+  finally:
+    directory.rmdir --recursive cache-dir