1 files changed, 132 insertions, 0 deletions
diff --git a/cli/compat/mod.rs b/cli/compat/mod.rs
new file mode 100644
index 000000000..b95b65ddb
--- /dev/null
+++ b/cli/compat/mod.rs
@@ -0,0 +1,132 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+mod errors;
+mod esm_resolver;
+
+use deno_core::error::AnyError;
+use deno_core::located_script_name;
+use deno_core::url::Url;
+use deno_core::JsRuntime;
+
+pub use esm_resolver::NodeEsmResolver;
+
+// TODO(bartlomieju): this needs to be bumped manually for
+// each release, a better mechanism is preferable, but it's a quick and dirty
+// solution to avoid printing `X-Deno-Warning` headers when the compat layer is
+// downloaded
+static STD_URL_STR: &str = "https://deno.land/std@0.112.0/";
+
+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",
+];
+
+lazy_static::lazy_static! {
+  static ref GLOBAL_URL_STR: String = format!("{}node/global.ts", STD_URL_STR);
+  pub(crate) static ref GLOBAL_URL: Url = Url::parse(&GLOBAL_URL_STR).unwrap();
+  static ref MODULE_URL_STR: String = format!("{}node/module.ts", STD_URL_STR);
+  pub(crate) static ref MODULE_URL: Url = Url::parse(&MODULE_URL_STR).unwrap();
+  static ref COMPAT_IMPORT_URL: Url = Url::parse("flags:compat").unwrap();
+}
+
+/// Provide imports into a module graph when the compat flag is true.
+pub(crate) fn get_node_imports() -> Vec<(Url, Vec<String>)> {
+  vec![(COMPAT_IMPORT_URL.clone(), vec![GLOBAL_URL_STR.clone()])]
+}
+
+fn try_resolve_builtin_module(specifier: &str) -> Option<Url> {
+  if SUPPORTED_MODULES.contains(&specifier) {
+    let module_url = format!("{}node/{}.ts", STD_URL_STR, specifier);
+    Some(Url::parse(&module_url).unwrap())
+  } else {
+    None
+  }
+}
+
+pub async fn check_if_should_use_esm_loader(
+  js_runtime: &mut JsRuntime,
+  main_module: &str,
+) -> Result<bool, AnyError> {
+  // Decide if we're running with Node ESM loader or CJS loader.
+  let source_code = &format!(
+    r#"(async function checkIfEsm(main) {{
+      const {{ resolveMainPath, shouldUseESMLoader }} = await import("{}");
+      const resolvedMain = resolveMainPath(main);
+      const useESMLoader = shouldUseESMLoader(resolvedMain);
+      return useESMLoader;
+    }})('{}');"#,
+    MODULE_URL_STR.as_str(),
+    escape_for_single_quote_string(main_module),
+  );
+  let result =
+    js_runtime.execute_script(&located_script_name!(), source_code)?;
+  let use_esm_loader_global = js_runtime.resolve_value(result).await?;
+  let use_esm_loader = {
+    let scope = &mut js_runtime.handle_scope();
+    let use_esm_loader_local = use_esm_loader_global.get(scope);
+    use_esm_loader_local.boolean_value(scope)
+  };
+
+  Ok(use_esm_loader)
+}
+
+pub fn load_cjs_module(
+  js_runtime: &mut JsRuntime,
+  main_module: &str,
+) -> Result<(), AnyError> {
+  let source_code = &format!(
+    r#"(async function loadCjsModule(main) {{
+      const Module = await import("{}");
+      Module.default._load(main, null, true);
+    }})('{}');"#,
+    MODULE_URL_STR.as_str(),
+    escape_for_single_quote_string(main_module),
+  );
+
+  js_runtime.execute_script(&located_script_name!(), source_code)?;
+  Ok(())
+}
+
+fn escape_for_single_quote_string(text: &str) -> String {
+  text.replace(r"\", r"\\").replace("'", r"\'")
+}