feat(12135): Adding support for list access using env variables

inject/src/main/java/io/micronaut/context/env/EnvironmentPropertySource.java

@@ -17,9 +17,10 @@
 
 import io.micronaut.core.annotation.Nullable;
 
-import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.regex.Pattern;
 
 /**
  * Loads properties from environment variables via {@link System#getenv()}.
@@ -28,6 +29,10 @@
  * @since 1.0
  */
 public class EnvironmentPropertySource extends MapPropertySource {
+    /**
+     * Converts list elements defined as _0 or _0_ into names that the resolver can understand; i.e., [0].
+     */
+    private static final Pattern LIST_CONVERTER_REGEX = Pattern.compile("_([0-9]{1,2})(?:_|$)");
 
     /**
      * The position of the loader.
@@ -77,20 +82,21 @@ static Map getEnv(@Nullable List<String> includes, @Nullable List<String> exclud
     }
 
     static Map getEnv(Map<String, String> env, @Nullable List<String> includes, @Nullable List<String> excludes) {
-        if (includes != null || excludes != null) {
-            Map<String, String> result = new HashMap<>();
-            for (Map.Entry<String, String> entry : env.entrySet()) {
-                String envVar = entry.getKey();
-                if (excludes != null && excludes.contains(envVar)) {
-                    continue;
-                }
-                if (includes != null && !includes.contains(envVar)) {
-                    continue;
-                }
-                result.put(envVar, entry.getValue());
+        Map<String, String> result = new LinkedHashMap<>();
+        for (Map.Entry<String, String> entry : env.entrySet()) {
+            String envVar = entry.getKey();
+            if (excludes != null && excludes.contains(envVar)) {
+                continue;
+            }
+            if (includes != null && !includes.contains(envVar)) {
+                continue;
             }
-            return result;
+
+            String convertedEnvVar = LIST_CONVERTER_REGEX.matcher(envVar).replaceAll("[$1]");
+
+            result.put(convertedEnvVar, entry.getValue());
         }
-        return env;
+
+        return result;
     }
 }

inject/src/test/groovy/io/micronaut/context/env/EnvironmentPropertySourceSpec.groovy

@@ -88,5 +88,25 @@ class EnvironmentPropertySourceSpec extends Specification {
         cleanup:
         context.close()
     }
-
+
+    void "test environment variable list conversion scenarios"() {
+        def envs = SystemLambda.withEnvironmentVariable("A_0", "valueA")
+                .and("A_0__B", "nestedValueB")
+                .and("A_0__C_0", "multipleArraysC")
+
+        ApplicationContext context = envs.execute(() -> ApplicationContext.builder().start())
+
+        expect:
+        context.getProperty("a[0]", String).isPresent()
+        context.getRequiredProperty("a[0]", String) == "valueA"
+
+        context.getProperty("a[0].b", String).isPresent()
+        context.getRequiredProperty("a[0].b", String) == "nestedValueB"
+
+        context.getProperty("a[0].c[0]", String).isPresent()
+        context.getRequiredProperty("a[0].c[0]", String) == "multipleArraysC"
+
+        cleanup:
+        context.close()
+    }
 }