Allow nested square brackets in map key when binding

Fixes gh-3202

spring-boot/src/main/java/org/springframework/boot/context/properties/source/ConfigurationPropertyName.java

@@ -513,18 +513,25 @@ public final class ConfigurationPropertyName
 		int start = 0;
 		boolean indexed = false;
 		int length = name.length();
+		int openBracketCount = 0;
 		for (int i = 0; i < length; i++) {
 			char ch = name.charAt(i);
-			if (indexed && ch == ']') {
+			if (ch == ']') {
+				openBracketCount--;
+				if (openBracketCount == 0) {
 					processElement(processor, name, start, i + 1, indexed);
 					start = i + 1;
 					indexed = false;
 				}
-			else if (!indexed && ch == '[') {
+			}
+			else if (ch == '[') {
+				openBracketCount++;
+				if (!indexed) {
 					processElement(processor, name, start, i, indexed);
 					start = i;
 					indexed = true;
 				}
+			}
 			else if (!indexed && ch == separator) {
 				processElement(processor, name, start, i, indexed);
 				start = i + 1;

spring-boot/src/test/java/org/springframework/boot/context/properties/bind/MapBinderTests.java

@@ -503,6 +503,15 @@ public class MapBinderTests {
 		assertThat(map.get(0)).containsExactly(8, 9);
 	}
 
+	@Test
+	public void bindingWithSquareBracketMap() throws Exception {
+		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
+		source.put("foo.[x [B] y]", "[ball]");
+		this.sources.add(source);
+		Map<String, String> map = this.binder.bind("foo", STRING_STRING_MAP).get();
+		assertThat(map).containsEntry("x [B] y", "[ball]");
+	}
+
 	private <K, V> Bindable<Map<K, V>> getMapBindable(Class<K> keyGeneric, ResolvableType valueType) {
 		ResolvableType keyType = ResolvableType.forClass(keyGeneric);
 		return Bindable.of(ResolvableType.forClassWithGenerics(Map.class, keyType, valueType));

spring-boot/src/test/java/org/springframework/boot/context/properties/source/ConfigurationPropertyNameTests.java

@@ -175,6 +175,21 @@ public class ConfigurationPropertyNameTests {
 		ConfigurationPropertyName.of("bar]");
 	}
 
+	@Test
+	public void ofNameWhenMultipleMismatchedBrackets() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("is not valid");
+		ConfigurationPropertyName.of("[a[[[b]ar]");
+	}
+
+	@Test
+	public void ofNameWhenNestedBrackets() throws Exception {
+		ConfigurationPropertyName name = ConfigurationPropertyName.of("foo[a[c][[b]ar]]");
+		assertThat(name.toString()).isEqualTo("foo[a[c][[b]ar]]");
+		assertThat(name.getElement(0, Form.ORIGINAL)).isEqualTo("foo");
+		assertThat(name.getElement(1, Form.ORIGINAL)).isEqualTo("a[c][[b]ar]");
+	}
+
 	@Test
 	public void ofNameWithWhitespaceInName() throws Exception {
 		this.thrown.expect(IllegalArgumentException.class);