Add the ability to assign env vars to lists

Resolves sksamuel#402.

README.md

@@ -197,6 +197,8 @@ Hoplite maps env vars as follows:
 
 * Underscores are separators for nested config. For example `TOPIC_NAME` would override a property `name` located in a `topic` parent.
 
+* To bind env vars to arrays or lists, postfix with an index e.g. set env vars `TOPIC_NAME_0` and `TOPIC_NAME_1` to set two values for the `name` list property. Missing indices are ignored, which is useful for commenting out values without renumbering subsequent ones.
+
 * To bind env vars to maps, the key is part of the nested config e.g. `TOPIC_NAME_FOO` and `TOPIC_NAME_BAR` would set the "foo" and "bar"
 keys for the `name` map property. Note that keys are one exception to the idiomatic uppercase rule -- the env var name determines the
 case of the map key.

changelog.md

@@ -7,6 +7,7 @@ case is still accepted), letters, and digits. **Single underscores** now separat
 * Breaking: The `EnvironmentVariableOverridePropertySource` has been removed. The standard `EnvironmentVariablesPropertySource` is now
 loaded by default, and takes precedence over other default sources just like the `EnvironmentVariableOverridePropertySource`
 did. To maintain similar behavior, configure it with a filtering `prefix`.
+* Add the ability to load a series of environment variables into arrays/lists via the `_n` syntax.
 
 ### 2.7.5
 

hoplite-core/src/main/kotlin/com/sksamuel/hoplite/sources/EnvironmentVariablesPropertySource.kt

@@ -1,11 +1,14 @@
 package com.sksamuel.hoplite.sources
 
+import com.sksamuel.hoplite.ArrayNode
 import com.sksamuel.hoplite.ConfigResult
+import com.sksamuel.hoplite.MapNode
 import com.sksamuel.hoplite.Node
 import com.sksamuel.hoplite.PropertySource
 import com.sksamuel.hoplite.PropertySourceContext
 import com.sksamuel.hoplite.fp.valid
 import com.sksamuel.hoplite.parsers.toNode
+import com.sksamuel.hoplite.transform
 
 class EnvironmentVariablesPropertySource(
   private val environmentVariableMap: () -> Map<String, String> = { System.getenv() },
@@ -23,6 +26,13 @@ class EnvironmentVariablesPropertySource(
       .filterKeys { if (prefix == null) true else it.startsWith(prefix) }
       .mapKeys { if (prefix == null) it.key else it.key.removePrefix(prefix) }
 
-    return map.toNode("env", DELIMITER).valid()
+    return map.toNode("env", DELIMITER).transform { node ->
+      if (node is MapNode && node.map.keys.all { it.toIntOrNull() != null }) {
+        // all they map keys are ints, so lets transform the MapNode into an ArrayNode
+        ArrayNode(node.map.values.toList(), node.pos, node.path, node.meta, node.delimiter, node.sourceKey)
+      } else {
+        node
+      }
+    }.valid()
   }
 }

hoplite-core/src/test/kotlin/com/sksamuel/hoplite/EnvironmentVariablesPropertySourceTest.kt

@@ -97,6 +97,87 @@ class EnvironmentVariablesPropertySourceTest : FunSpec({
     ))
   }
 
+  test("build env source can create lists") {
+    data class TestConfig(val listProp: List<String>)
+
+    val config = ConfigLoaderBuilder
+      .defaultWithoutPropertySources()
+      .addPropertySource(
+        EnvironmentVariablesPropertySource(
+          environmentVariableMap = {
+            mapOf(
+              "LISTPROP_0" to "value_a",
+              "LISTPROP_1" to "value_A",
+              "LISTPROP_2" to "value_abc",
+            )
+          },
+        )
+      )
+      .build()
+      .loadConfigOrThrow<TestConfig>()
+
+    config shouldBe TestConfig(listOf(
+      "value_a",
+      "value_A",
+      "value_abc",
+    ))
+  }
+
+  test("build env source can create intermediate lists") {
+    data class ListEntry(val foo: String)
+    data class TestConfig(val listProp: List<ListEntry>)
+
+    val config = ConfigLoaderBuilder
+      .defaultWithoutPropertySources()
+      .addPropertySource(
+        EnvironmentVariablesPropertySource(
+          environmentVariableMap = {
+            mapOf(
+              "LISTPROP_0_FOO" to "value_a",
+              "LISTPROP_1_FOO" to "value_A",
+              "LISTPROP_2_FOO" to "value_abc",
+            )
+          },
+        )
+      )
+      .build()
+      .loadConfigOrThrow<TestConfig>()
+
+    config shouldBe TestConfig(listOf(
+      ListEntry("value_a"),
+      ListEntry("value_A"),
+      ListEntry("value_abc"),
+    ))
+  }
+
+
+  test("build env source can skip missing list indices") {
+    // this is handy to easily comment out env vars without breaking the functionality
+
+    data class ListEntry(val foo: String)
+    data class TestConfig(val listProp: List<ListEntry>)
+
+    val config = ConfigLoaderBuilder
+      .defaultWithoutPropertySources()
+      .addPropertySource(
+        EnvironmentVariablesPropertySource(
+          environmentVariableMap = {
+            mapOf(
+              "LISTPROP_0_FOO" to "value_a",
+              "LISTPROP_2_FOO" to "value_abc",
+            )
+          },
+        )
+      )
+      .build()
+      .loadConfigOrThrow<TestConfig>()
+
+    config shouldBe TestConfig(listOf(
+      ListEntry("value_a"),
+      ListEntry("value_abc"),
+    ))
+  }
+
   test("env var source should respect config aliases that need to be normalized to match") {
     data class TestConfig(@ConfigAlias("fooBar") val bazBar: String)