Reject configuration property names with a repeated separator

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

@@ -672,6 +672,19 @@ private static Elements probablySingleElementOf(CharSequence name) {
 			}
 			throw new InvalidConfigurationPropertyNameException(name, Collections.singletonList('.'));
 		}
+		for (int i = 0; i < name.length() - 1; i++) {
+			if (name.charAt(i) == '.' && name.charAt(i + 1) == '.') {
+				// A repeated separator produces an empty element between the two dots.
+				// ElementsParser.add silently drops empty elements, which would
+				// otherwise make this name indistinguishable from the same name with
+				// the repeated separator collapsed to one (e.g. "foo..bar" parsing as
+				// identical to "foo.bar"), silently merging two distinct names.
+				if (returnNullIfInvalid) {
+					return null;
+				}
+				throw new InvalidConfigurationPropertyNameException(name, Collections.singletonList('.'));
+			}
+		}
 		if (name.charAt(name.length() - 1) == '[') {
 			if (returnNullIfInvalid) {
 				return null;

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

@@ -54,6 +54,22 @@ void ofNameShouldNotEndWithDot() {
 			.withMessageContaining("is not valid");
 	}
 
+	@Test
+	void ofNameShouldNotContainDoubleDot() {
+		// A repeated separator produces an empty element, which ElementsParser.add
+		// silently drops. Without this check, "foo..bar" parses as identical to
+		// "foo.bar" (of("foo..bar").equals(of("foo.bar")) is true and
+		// isValid("foo..bar") is true), so two distinct property-source keys that
+		// differ only by a repeated separator silently collide on the same
+		// ConfigurationPropertyName.
+		assertThatExceptionOfType(InvalidConfigurationPropertyNameException.class)
+			.isThrownBy(() -> ConfigurationPropertyName.of("foo..bar"))
+			.withMessageContaining("is not valid");
+		assertThatExceptionOfType(InvalidConfigurationPropertyNameException.class)
+			.isThrownBy(() -> ConfigurationPropertyName.of("foo...bar"))
+			.withMessageContaining("is not valid");
+	}
+
 	@Test
 	void ofNameShouldNotContainUppercase() {
 		assertThatExceptionOfType(InvalidConfigurationPropertyNameException.class)
@@ -757,6 +773,8 @@ void isValidWhenNotValidShouldReturnFalse() {
 		assertThat(ConfigurationPropertyName.isValid("-foo")).isFalse();
 		assertThat(ConfigurationPropertyName.isValid("FooBar")).isFalse();
 		assertThat(ConfigurationPropertyName.isValid("foo!bar")).isFalse();
+		assertThat(ConfigurationPropertyName.isValid("foo..bar")).isFalse();
+		assertThat(ConfigurationPropertyName.isValid("foo...bar")).isFalse();
 		assertThat(ConfigurationPropertyName.isValid("foo[")).isFalse();
 	}