Virtual file support (#701)

* Add support for virtual files (eg, not backed by an OS file).

Virtual files are implemented through trait objects, with a default
implementation that tries to behave like on-disk files, but entirely
backed by in-memory structures.

Co-authored-by: Dan Gohman <sunfish@mozilla.com>

crates/test-programs/wasi-tests/src/bin/fd_flags_set.rs

@@ -50,7 +50,7 @@ unsafe fn test_fd_fdstat_set_flags(dir_fd: wasi::Fd) {
         )
         .expect("reading file"),
         buffer.len(),
-        "shoudl read {} bytes",
+        "should read {} bytes",
         buffer.len()
     );
 
@@ -87,7 +87,7 @@ unsafe fn test_fd_fdstat_set_flags(dir_fd: wasi::Fd) {
         )
         .expect("reading file"),
         buffer.len(),
-        "shoudl read {} bytes",
+        "should read {} bytes",
         buffer.len()
     );
 
@@ -126,7 +126,7 @@ unsafe fn test_fd_fdstat_set_flags(dir_fd: wasi::Fd) {
         )
         .expect("reading file"),
         buffer.len(),
-        "shoudl read {} bytes",
+        "should read {} bytes",
         buffer.len()
     );
 

crates/test-programs/wasi-tests/src/bin/remove_directory_trailing_slashes.rs

@@ -11,14 +11,14 @@ unsafe fn test_remove_directory_trailing_slashes(dir_fd: wasi::Fd) {
 
     wasi::path_create_directory(dir_fd, "dir").expect("creating a directory");
 
-    // Test that removing it with a trailing flash succeeds.
+    // Test that removing it with a trailing slash succeeds.
     wasi::path_remove_directory(dir_fd, "dir/")
         .expect("remove_directory with a trailing slash on a directory should succeed");
 
     // Create a temporary file.
     create_file(dir_fd, "file");
 
-    // Test that removing it with no trailing flash fails.
+    // Test that removing it with no trailing slash fails.
     assert_eq!(
         wasi::path_remove_directory(dir_fd, "file")
             .expect_err("remove_directory without a trailing slash on a file should fail")
@@ -27,7 +27,7 @@ unsafe fn test_remove_directory_trailing_slashes(dir_fd: wasi::Fd) {
         "errno should be ERRNO_NOTDIR"
     );
 
-    // Test that removing it with a trailing flash fails.
+    // Test that removing it with a trailing slash fails.
     assert_eq!(
         wasi::path_remove_directory(dir_fd, "file/")
             .expect_err("remove_directory with a trailing slash on a file should fail")