feat: add --compat flag to provide built-in Node modules (#12293)

This commit adds "--compat" flag. When the flag is passed a set of mappings for
built-in Node modules is injected into the import map. If user doesn't
explicitly provide an import map (using "--import-map" flag) then a map is
created on the fly. If there are already existing mappings in import map that
would clash with built-in Node modules a set of diagnostics is printed to the
terminal with suggestions how to proceed.

cli/Cargo.toml

@@ -59,7 +59,7 @@ encoding_rs = "0.8.28"
 env_logger = "0.8.4"
 fancy-regex = "0.7.1"
 http = "0.2.4"
-import_map = "0.3.0"
+import_map = "0.3.3"
 jsonc-parser = { version = "0.17.0", features = ["serde"] }
 lazy_static = "1.4.0"
 libc = "0.2.101"

cli/compat.rs

@@ -0,0 +1,60 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+use std::collections::HashMap;
+
+static SUPPORTED_MODULES: &[&str] = &[
+  "assert",
+  "assert/strict",
+  "async_hooks",
+  "buffer",
+  "child_process",
+  "cluster",
+  "console",
+  "constants",
+  "crypto",
+  "dgram",
+  "dns",
+  "domain",
+  "events",
+  "fs",
+  "fs/promises",
+  "http",
+  "https",
+  "module",
+  "net",
+  "os",
+  "path",
+  "path/posix",
+  "path/win32",
+  "perf_hooks",
+  "process",
+  "querystring",
+  "readline",
+  "stream",
+  "stream/promises",
+  "stream/web",
+  "string_decoder",
+  "sys",
+  "timers",
+  "timers/promises",
+  "tls",
+  "tty",
+  "url",
+  "util",
+  "util/types",
+  "v8",
+  "vm",
+  "zlib",
+];
+
+pub fn get_mapped_node_builtins() -> HashMap<String, String> {
+  let mut mappings = HashMap::new();
+
+  for module in SUPPORTED_MODULES {
+    // TODO(bartlomieju): this is unversioned, and should be fixed to use latest stable?
+    let module_url = format!("https://deno.land/std/node/{}.ts", module);
+    mappings.insert(module.to_string(), module_url);
+  }
+
+  mappings
+}

cli/flags.rs

@@ -222,6 +222,9 @@ pub struct Flags {
   pub log_level: Option<Level>,
   pub no_check: bool,
   pub no_remote: bool,
+  /// If true, a list of Node built-in modules will be injected into
+  /// the import map.
+  pub compat: bool,
   pub prompt: bool,
   pub reload: bool,
   pub repl: bool,
@@ -1490,6 +1493,7 @@ fn runtime_args<'a, 'b>(
     .arg(v8_flags_arg())
     .arg(seed_arg())
     .arg(enable_testing_features_arg())
+    .arg(compat_arg())
 }
 
 fn inspect_args<'a, 'b>(app: App<'a, 'b>) -> App<'a, 'b> {
@@ -1619,6 +1623,12 @@ fn seed_arg<'a, 'b>() -> Arg<'a, 'b> {
     })
 }
 
+fn compat_arg<'a, 'b>() -> Arg<'a, 'b> {
+  Arg::with_name("compat")
+    .long("compat")
+    .help("Node compatibility mode. Currently only enables built-in node modules like 'fs'.")
+}
+
 fn watch_arg<'a, 'b>() -> Arg<'a, 'b> {
   Arg::with_name("watch")
     .long("watch")
@@ -2228,6 +2238,7 @@ fn runtime_args_parse(
   location_arg_parse(flags, matches);
   v8_flags_arg_parse(flags, matches);
   seed_arg_parse(flags, matches);
+  compat_arg_parse(flags, matches);
   inspect_arg_parse(flags, matches);
   enable_testing_features_arg_parse(flags, matches);
 }
@@ -2313,6 +2324,12 @@ fn seed_arg_parse(flags: &mut Flags, matches: &ArgMatches) {
   }
 }
 
+fn compat_arg_parse(flags: &mut Flags, matches: &ArgMatches) {
+  if matches.is_present("compat") {
+    flags.compat = true;
+  }
+}
+
 fn no_check_arg_parse(flags: &mut Flags, matches: &clap::ArgMatches) {
   if matches.is_present("no-check") {
     flags.no_check = true;
@@ -4431,4 +4448,19 @@ mod tests {
       .to_string()
       .contains("Expected protocol \"http\" or \"https\""));
   }
+
+  #[test]
+  fn compat() {
+    let r = flags_from_vec(svec!["deno", "run", "--compat", "foo.js"]);
+    assert_eq!(
+      r.unwrap(),
+      Flags {
+        subcommand: DenoSubcommand::Run(RunFlags {
+          script: "foo.js".to_string(),
+        }),
+        compat: true,
+        ..Flags::default()
+      }
+    );
+  }
 }

cli/main.rs

@@ -3,6 +3,7 @@
 mod ast;
 mod auth_tokens;
 mod checksum;
+mod compat;
 mod config_file;
 mod deno_dir;
 mod diagnostics;

cli/proc_state.rs

@@ -36,6 +36,7 @@ use deno_tls::rustls_native_certs::load_native_certs;
 use deno_tls::webpki_roots::TLS_SERVER_ROOTS;
 use import_map::ImportMap;
 use log::debug;
+use log::info;
 use log::warn;
 use std::collections::HashMap;
 use std::collections::HashSet;
@@ -182,7 +183,7 @@ impl ProcState {
         None
       };
 
-    let maybe_import_map: Option<ImportMap> =
+    let mut maybe_import_map: Option<ImportMap> =
       match flags.import_map_path.as_ref() {
         None => None,
         Some(import_map_url) => {
@@ -204,6 +205,32 @@ impl ProcState {
         }
       };
 
+    if flags.compat {
+      let mut import_map = match maybe_import_map {
+        Some(import_map) => import_map,
+        None => {
+          // INFO: we're creating an empty import map, with its specifier pointing
+          // to `CWD/node_import_map.json` to make sure the map still works as expected.
+          let import_map_specifier =
+            std::env::current_dir()?.join("node_import_map.json");
+          ImportMap::from_json(import_map_specifier.to_str().unwrap(), "{}")
+            .unwrap()
+        }
+      };
+      let node_builtins = crate::compat::get_mapped_node_builtins();
+      let diagnostics = import_map.update_imports(node_builtins)?;
+
+      if !diagnostics.is_empty() {
+        info!("Some Node built-ins were not added to the import map:");
+        for diagnostic in diagnostics {
+          info!("  - {}", diagnostic);
+        }
+        info!("If you want to use Node built-ins provided by Deno remove listed specifiers from \"imports\" mapping in the import map file.");
+      }
+
+      maybe_import_map = Some(import_map);
+    }
+
     let maybe_inspect_host = flags.inspect.or(flags.inspect_brk);
     let maybe_inspector_server = maybe_inspect_host.map(|host| {
       Arc::new(InspectorServer::new(host, version::get_user_agent()))

cli/tests/integration/compat_tests.rs

@@ -0,0 +1,14 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+use crate::itest;
+
+itest!(fs_promises {
+  args: "run --compat --unstable -A compat/fs_promises.js",
+  output: "compat/fs_promises.out",
+});
+
+itest!(existing_import_map {
+  args: "run --compat --import-map compat/existing_import_map.json compat/fs_promises.js",
+  output: "compat/existing_import_map.out",
+  exit_code: 1,
+});

cli/tests/integration/mod.rs

@@ -54,6 +54,8 @@ macro_rules! itest_flaky(
 mod bundle;
 #[path = "cache_tests.rs"]
 mod cache;
+#[path = "compat_tests.rs"]
+mod compat;
 #[path = "compile_tests.rs"]
 mod compile;
 #[path = "coverage_tests.rs"]

cli/tests/testdata/compat/existing_import_map.json

@@ -0,0 +1,5 @@
+{
+  "imports": {
+    "fs/promises": "./non_existent_file.js"
+  }
+}

cli/tests/testdata/compat/existing_import_map.out

@@ -0,0 +1,5 @@
+[WILDCARD]
+Some Node built-ins were not added to the import map:
+  - "fs/promises" already exists and is mapped to "[WILDCARD]non_existent_file.js"
+If you want to use Node built-ins provided by Deno remove listed specifiers from "imports" mapping in the import map file.
+error: Cannot resolve module [WILDCARD]

cli/tests/testdata/compat/fs_promises.js

@@ -0,0 +1,3 @@
+import fs from "fs/promises";
+const data = await fs.readFile("compat/test.txt", "utf-8");
+console.log(data);

cli/tests/testdata/compat/fs_promises.out

@@ -0,0 +1,2 @@
+[WILDCARD]
+This is some example text that will be read using compatiblity mode.

cli/tests/testdata/compat/test.txt

@@ -0,0 +1 @@
+This is some example text that will be read using compatiblity mode.

cli/tools/standalone.rs

@@ -227,6 +227,7 @@ pub fn compile_to_runtime_flags(
     lock: None,
     log_level: flags.log_level,
     no_check: false,
+    compat: flags.compat,
     unsafely_ignore_certificate_errors: flags
       .unsafely_ignore_certificate_errors,
     no_remote: false,