[vscode] fix resolution of env variables

- if an env variable does not exist it should resolve to an empty string to emulate the shell
- normalize env variable name to lower case in order to retrieve them from process.env on windows

Signed-off-by: Anton Kosyakov <anton.kosyakov@typefox.io>

packages/core/src/node/env-variables/env-variables-server.ts

@@ -16,6 +16,7 @@
 
 import { injectable } from 'inversify';
 import { EnvVariable, EnvVariablesServer } from '../../common/env-variables';
+import { isWindows } from '../../common/os';
 
 @injectable()
 export class EnvVariablesServerImpl implements EnvVariablesServer {
@@ -38,6 +39,9 @@ export class EnvVariablesServerImpl implements EnvVariablesServer {
     }
 
     async getValue(key: string): Promise<EnvVariable | undefined> {
+        if (isWindows) {
+            key = key.toLowerCase();
+        }
         return this.envs[key];
     }
 }

packages/variable-resolver/src/browser/common-variable-contribution.ts

@@ -56,7 +56,8 @@ export class CommonVariableContribution implements VariableContribution {
             name: 'env',
             resolve: async (_, envVariableName) => {
                 const envVariable = envVariableName && await this.env.getValue(envVariableName);
-                return envVariable && envVariable.value;
+                const envValue = envVariable && envVariable.value;
+                return envValue || '';
             }
         });
         variables.registerVariable({