Allow emscripten-releases-tags/aliases to work be used without SDK deps

This change means that aliases such as `latest` and `3.10.2` can be
used to install jsut the emscipten-releases packages and not the full
SDK with all the dependencies.

This allows uses who do not want to install dependencies such as node,
python or java to still use this package.

These packages were already available to install on their own via
their full names such as:

```
$ ./emsdk install releases-upstream-48ce0b44015d0182fc8c27aa9fbc0a4474b55982-64bi
```

Now these base packages can also be install via:

```
$ ./emsdk install latest-base
```

Fixes: #1142

Author: sbc100

emsdk.py

@@ -2323,11 +2323,17 @@ def load_file_index_list(filename):
 def load_releases_info():
   if not hasattr(load_releases_info, 'cached_info'):
     try:
-      text = open(sdk_path('emscripten-releases-tags.json'), 'r').read()
-      load_releases_info.cached_info = json.loads(text)
+      with open(sdk_path('emscripten-releases-tags.json')) as f:
+        text = f.read()
+      info = json.loads(text)
     except Exception as e:
       print('Error parsing emscripten-releases-tags.json!')
       exit_with_error(str(e))
+    for key, value in dict(info['aliases']).items():
+      info['aliases'][key + '-base'] = value + '-base'
+    for key, value in dict(info['releases']).items():
+      info['releases'][key + '-base'] = value + '-base'
+    load_releases_info.cached_info = info
 
   return load_releases_info.cached_info
 
@@ -2817,8 +2823,12 @@ def expand_sdk_name(name, activating):
   elif '-fastcomp' in fullname:
     fullname = fullname.replace('-fastcomp', '')
     backend = 'fastcomp'
-  version = fullname.replace('sdk-', '').replace('releases-', '').replace('-64bit', '').replace('tag-', '')
-  sdk = 'sdk-' if not name.startswith('releases-') else ''
+  version = name
+  for pattern in ('sdk-', 'releases-', '-64bit', 'tag-', '-base'):
+    version = version.replace(pattern, '')
+  sdk_prefix = 'sdk-'
+  if name.startswith('releases-') or name.endswith('-base'):
+    sdk_prefix = ''
   releases_info = load_releases_info()['releases']
   release_hash = get_release_hash(version, releases_info)
   if release_hash:
@@ -2830,7 +2840,7 @@ def expand_sdk_name(name, activating):
         backend = 'upstream'
       else:
         backend = 'fastcomp'
-    full_name = '%sreleases-%s-%s-64bit' % (sdk, backend, release_hash)
+    full_name = '%sreleases-%s-%s-64bit' % (sdk_prefix, backend, release_hash)
     print("Resolving SDK version '%s' to '%s'" % (version, full_name))
     return full_name
 
@@ -2839,7 +2849,7 @@ def expand_sdk_name(name, activating):
       backend = 'upstream'
     global extra_release_tag
     extra_release_tag = version
-    return '%sreleases-%s-%s-64bit' % (sdk, backend, version)
+    return '%sreleases-%s-%s-64bit' % (sdk_prefix, backend, version)
 
   return name
 

test/test.py

@@ -286,6 +286,12 @@ def test_install_tool(self):
     # Test that its possible to install emscripten as tool instead of SDK
     checked_call_with_output(emsdk + ' install releases-upstream-77b065ace39e6ab21446e13f92897f956c80476a', unexpected='Installing SDK')
 
+  def test_install_alias(self):
+    # 3.1.18 is 49d45744895c7d7e28acd94a385d7ee361653b4a
+    run_emsdk('install 3.1.18-base')
+    checked_call_with_output(emsdk + ' install install 3.1.18-base', unexpected='Installing SDK')
+    checked_call_with_output(emsdk + ' install install releases-upstream-49d45744895c7d7e28acd94a385d7ee361653b4a', unexpected='already downloaded, skipping', unexpected='Downloading:')
+
   def test_activate_missing(self):
     run_emsdk('install latest')
     failing_call_with_output(emsdk + ' activate 2.0.1', expected="error: tool is not installed and therefore cannot be activated: 'releases-upstream-13e29bd55185e3c12802bc090b4507901856b2ba-64bit'")