feat(add/install): default to npm registry for unprefixed packages (#33246)

Reland of #33156, which was reverted in #33214 to be relanded for Deno
v2.8.

---

Before:
```
$ deno install npm:express npm:react
$ deno install --npm express react
$ deno install jsr:@std/async
```
After:
```
$ deno install express react jsr:@std/async
```

Makes `deno add express` and `deno install express` work without
requiring the `npm:` prefix or `--npm` flag. Since npm is by far the
most common registry for package installation, this removes friction
for the most common use case.

The `--jsr` flag is still available to override the default to jsr,
and explicit `jsr:` / `npm:` prefixes always take precedence.

Author: bartlomieju

cli/args/flags.rs

@@ -2300,13 +2300,13 @@ fn add_subcommand() -> Command {
     "add",
     cstr!(
       "Add dependencies to your configuration file.
-  <p(245)>deno add jsr:@std/path</>
+  <p(245)>deno add express</>
 
-You can also add npm packages:
-  <p(245)>deno add npm:react</>
+Unprefixed packages default to npm. Use jsr: prefix for jsr packages:
+  <p(245)>deno add jsr:@std/path</>
 
 Or multiple dependencies at once:
-  <p(245)>deno add jsr:@std/path jsr:@std/assert npm:chalk</>"
+  <p(245)>deno add express jsr:@std/path</>"
     ),
     UnstableArgsConfig::None,
   )
@@ -2466,7 +2466,7 @@ fn default_registry_args() -> [Arg; 2] {
   [
     Arg::new("npm")
       .long("npm")
-      .help("assume unprefixed package names are npm packages")
+      .help("assume unprefixed package names are npm packages (default)")
       .action(ArgAction::SetTrue)
       .conflicts_with("jsr"),
     Arg::new("jsr")
@@ -3595,8 +3595,8 @@ in the package cache. If no dependency is specified, installs all dependencies l
 If the <p(245)>--entrypoint</> flag is passed, installs the dependencies of the specified entrypoint(s).
 
   <p(245)>deno install</>
+  <p(245)>deno install express</>
   <p(245)>deno install jsr:@std/bytes</>
-  <p(245)>deno install npm:chalk</>
   <p(245)>deno install --entrypoint entry1.ts entry2.ts</>
 
 <g>Global installation</>
@@ -6288,7 +6288,9 @@ fn add_parse_inner(
   } else if matches.get_flag("jsr") {
     Some(DefaultRegistry::Jsr)
   } else {
-    None
+    // Default to npm when no --npm or --jsr flag is provided.
+    // This allows `deno add express` to work without requiring `npm:` prefix.
+    Some(DefaultRegistry::Npm)
   };
   AddFlags {
     packages,
@@ -14427,7 +14429,7 @@ mod tests {
           mk_flags(AddFlags {
             packages: svec!["@david/which"],
             dev: false, // default is false
-            default_registry: None,
+            default_registry: Some(DefaultRegistry::Npm),
             lockfile_only: false,
             save_exact: false,
           })
@@ -14445,7 +14447,7 @@ mod tests {
         let mut expected_flags = mk_flags(AddFlags {
           packages: svec!["@david/which", "@luca/hello"],
           dev: false,
-          default_registry: None,
+          default_registry: Some(DefaultRegistry::Npm),
           lockfile_only: true,
           save_exact: false,
         });
@@ -14459,7 +14461,7 @@ mod tests {
           mk_flags(AddFlags {
             packages: svec!["npm:chalk"],
             dev: true,
-            default_registry: None,
+            default_registry: Some(DefaultRegistry::Npm),
             lockfile_only: false,
             save_exact: false,
           }),

cli/tools/pm/mod.rs

@@ -482,6 +482,9 @@ pub async fn add(
 
     match req {
       Ok(add_req) => package_reqs.push(add_req),
+      // Currently unreachable: default_registry is always Some (defaults to Npm),
+      // so parse() always resolves a prefix. Kept as a safety fallback in case
+      // the API is called with None from elsewhere.
       Err(package_req) => {
         if jsr_resolver
           .req_to_nv(&package_req)
@@ -848,7 +851,6 @@ impl AddRmPackageReq {
     }
 
     let (maybe_prefix, entry_text) = parse_prefix(entry_text);
-    let maybe_prefix = maybe_prefix.or(default_prefix);
     let (prefix, maybe_alias, entry_text) = match maybe_prefix {
       Some(prefix) => (prefix, None, entry_text),
       None => match parse_alias(entry_text) {
@@ -865,7 +867,10 @@ impl AddRmPackageReq {
             entry_text,
           )
         }
-        None => return Ok(Err(PackageReq::from_str(entry_text)?)),
+        None => match default_prefix {
+          Some(prefix) => (prefix, None, entry_text),
+          None => return Ok(Err(PackageReq::from_str(entry_text)?)),
+        },
       },
     };
 
@@ -1093,6 +1098,24 @@ mod test {
       (("jsr:foo", Some(Prefix::Jsr)), jsr_pkg_req("foo", "foo")),
       (("npm:foo", Some(Prefix::Jsr)), npm_pkg_req("foo", "foo@*")),
       (("jsr:foo", Some(Prefix::Npm)), jsr_pkg_req("foo", "foo")),
+      // Alias with explicit prefix still works when default is set
+      (
+        ("my-alias@npm:foo", Some(Prefix::Npm)),
+        npm_pkg_req("my-alias", "foo@*"),
+      ),
+      (
+        ("my-alias@jsr:foo", Some(Prefix::Npm)),
+        jsr_pkg_req("my-alias", "foo"),
+      ),
+      // Unprefixed without alias defaults to npm
+      (
+        ("chalk", Some(Prefix::Npm)),
+        npm_pkg_req("chalk", "chalk@*"),
+      ),
+      (
+        ("@scope/pkg", Some(Prefix::Npm)),
+        npm_pkg_req("@scope/pkg", "@scope/pkg@*"),
+      ),
     ];
 
     for ((input, maybe_prefix), expected) in cases {

tests/specs/add/missing_prefix/__test__.jsonc

@@ -1,15 +1,33 @@
 {
   "tempDir": true,
-  "steps": [
-    {
-      "args": "add ajv",
-      "output": "error: ajv is missing a prefix. Did you mean `deno add npm:ajv`?\n",
-      "exitCode": 1
+  "tests": {
+    // Unprefixed packages default to npm, so `deno add ajv` should work
+    "npm_default": {
+      "steps": [
+        {
+          "args": "add ajv",
+          "output": "Add npm:ajv@8.11.0\n[WILDCARD]\n"
+        }
+      ]
     },
-    {
-      "args": "add @std/testing",
-      "output": "error: @std/testing is missing a prefix. Did you mean `deno add jsr:@std/testing`?\n",
-      "exitCode": 1
+    // Packages that only exist on jsr should suggest using jsr: prefix
+    "jsr_needs_prefix": {
+      "steps": [
+        {
+          "args": "add @denotest/echo",
+          "output": "error: npm:@denotest/echo was not found, but a matching jsr package exists. Did you mean `deno add jsr:@denotest/echo`?\n",
+          "exitCode": 1
+        }
+      ]
+    },
+    // Using --jsr flag should still work for jsr packages
+    "jsr_flag_override": {
+      "steps": [
+        {
+          "args": "add --jsr @denotest/add",
+          "output": "Add jsr:@denotest/add@1.0.0\n[WILDCARD]\n"
+        }
+      ]
     }
-  ]
+  }
 }

tests/specs/add/npm_default/__test__.jsonc

@@ -0,0 +1,67 @@
+{
+  "tempDir": true,
+  "tests": {
+    // Unprefixed package name should resolve as npm by default
+    "add_unprefixed": {
+      "args": "add @denotest/esm-basic",
+      "output": "add_unprefixed.out"
+    },
+    // Mixing unprefixed (npm default) with explicit jsr: prefix
+    "add_mixed_with_jsr": {
+      "args": "add @denotest/esm-basic jsr:@denotest/add",
+      "output": "add_mixed.out"
+    },
+    // install subcommand should also default to npm
+    "install_unprefixed": {
+      "args": "install @denotest/esm-basic",
+      "output": "add_unprefixed.out"
+    },
+    // Explicit npm: prefix still works (backward compat)
+    "add_explicit_npm_prefix": {
+      "args": "add npm:@denotest/esm-basic",
+      "output": "add_unprefixed.out"
+    },
+    // --jsr flag overrides default to jsr
+    "add_jsr_flag": {
+      "args": "add --jsr @denotest/add",
+      "output": "add_jsr_flag.out"
+    },
+    // --npm flag is now a no-op (same as default) but should still work
+    "add_npm_flag_noop": {
+      "args": "add --npm @denotest/esm-basic",
+      "output": "add_unprefixed.out"
+    },
+    // Alias with explicit npm: prefix still works when default is npm
+    "add_alias_with_prefix": {
+      "steps": [
+        {
+          "args": "add my-alias@npm:@denotest/esm-basic",
+          "output": "Add npm:@denotest/esm-basic@1.0.0\n[WILDCARD]\n"
+        },
+        {
+          "args": [
+            "eval",
+            "console.log(JSON.stringify(JSON.parse(Deno.readTextFileSync('deno.json')).imports))"
+          ],
+          "output": "{\"my-alias\":\"npm:@denotest/esm-basic@^1.0.0\"}\n"
+        }
+      ]
+    },
+    // Alias with jsr: prefix works even when default is npm
+    "add_alias_jsr_prefix": {
+      "steps": [
+        {
+          "args": "add my-jsr@jsr:@denotest/add",
+          "output": "Add jsr:@denotest/add@1.0.0\n[WILDCARD]\n"
+        },
+        {
+          "args": [
+            "eval",
+            "console.log(JSON.stringify(JSON.parse(Deno.readTextFileSync('deno.json')).imports))"
+          ],
+          "output": "{\"my-jsr\":\"jsr:@denotest/add@^1.0.0\"}\n"
+        }
+      ]
+    }
+  }
+}

tests/specs/add/npm_default/add_jsr_flag.out

@@ -0,0 +1,2 @@
+Add jsr:@denotest/add@1.0.0
+Download http://127.0.0.1:4250/@denotest/add/1.0.0/mod.ts

tests/specs/add/npm_default/add_mixed.out

@@ -0,0 +1,11 @@
+Add npm:@denotest/esm-basic@1.0.0
+Add jsr:@denotest/add@1.0.0
+[UNORDERED_START]
+Download http://localhost:4260/@denotest%2fesm-basic
+Download http://127.0.0.1:4250/@denotest/add/1.0.0/mod.ts
+Download http://localhost:4260/@denotest/esm-basic/1.0.0.tgz
+[UNORDERED_END]
+
+Dependencies:
++ npm:@denotest/esm-basic 1.0.0
+

tests/specs/add/npm_default/add_unprefixed.out

@@ -0,0 +1,9 @@
+Add npm:@denotest/esm-basic@1.0.0
+[UNORDERED_START]
+Download http://localhost:4260/@denotest%2fesm-basic
+Download http://localhost:4260/@denotest/esm-basic/1.0.0.tgz
+[UNORDERED_END]
+
+Dependencies:
++ npm:@denotest/esm-basic 1.0.0
+

tests/specs/add/npm_default/deno.json

@@ -0,0 +1 @@
+{}

tests/specs/install/npm_default/__test__.jsonc

@@ -0,0 +1,20 @@
+{
+  "tempDir": true,
+  "tests": {
+    // Unprefixed package name should resolve as npm by default
+    "install_unprefixed": {
+      "args": "install @denotest/esm-basic",
+      "output": "install_unprefixed.out"
+    },
+    // Explicit npm: prefix still works (backward compat)
+    "install_explicit_npm_prefix": {
+      "args": "install npm:@denotest/esm-basic",
+      "output": "install_unprefixed.out"
+    },
+    // --jsr flag overrides default to jsr
+    "install_jsr_flag": {
+      "args": "install --jsr @denotest/add",
+      "output": "install_jsr_flag.out"
+    }
+  }
+}

tests/specs/install/npm_default/deno.json

@@ -0,0 +1 @@
+{}