Allow trailing whitespace document split marker

Refine `OriginTrackedPropertiesLoader` document split detection to be
more lenient if there is trailing whitespace.

Closes gh-23399

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/OriginTrackedPropertiesLoader.java

@@ -57,8 +57,7 @@ class OriginTrackedPropertiesLoader {
 	}
 
 	/**
-	 * Load {@code .properties} data and return a map of {@code String} ->
-	 * {@link OriginTrackedValue}.
+	 * Load {@code .properties} data and return a list of documents.
 	 * @return the loaded properties
 	 * @throws IOException on read error
 	 */
@@ -79,7 +78,7 @@ class OriginTrackedPropertiesLoader {
 		try (CharacterReader reader = new CharacterReader(this.resource)) {
 			StringBuilder buffer = new StringBuilder();
 			while (reader.read()) {
-				if (reader.getCharacter() == '#') {
+				if (reader.isPoundCharacter()) {
 					if (isNewDocument(reader)) {
 						if (!document.isEmpty()) {
 							result.add(document);
@@ -150,12 +149,13 @@ class OriginTrackedPropertiesLoader {
 	}
 
 	boolean isNewDocument(CharacterReader reader) throws IOException {
-		boolean result = reader.isPoundCharacter();
+		boolean result = reader.getLocation().getColumn() == 0 && reader.isPoundCharacter();
 		result = result && readAndExpect(reader, reader::isHyphenCharacter);
 		result = result && readAndExpect(reader, reader::isHyphenCharacter);
 		result = result && readAndExpect(reader, reader::isHyphenCharacter);
-		result = result && readAndExpect(reader, reader::isEndOfLine);
-		return result;
+		reader.read();
+		reader.skipWhitespace();
+		return result && reader.isEndOfLine();
 	}
 
 	private boolean readAndExpect(CharacterReader reader, BooleanSupplier check) throws IOException {
@@ -198,7 +198,7 @@ class OriginTrackedPropertiesLoader {
 			this.character = this.reader.read();
 			this.columnNumber++;
 			if (this.columnNumber == 0) {
-				skipLeadingWhitespace();
+				skipWhitespace();
 				if (!wrappedLine) {
 					if (this.character == '!') {
 						skipComment();
@@ -215,7 +215,7 @@ class OriginTrackedPropertiesLoader {
 			return !isEndOfFile();
 		}
 
-		private void skipLeadingWhitespace() throws IOException {
+		private void skipWhitespace() throws IOException {
 			while (isWhiteSpace()) {
 				this.character = this.reader.read();
 				this.columnNumber++;

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/env/OriginTrackedPropertiesLoaderTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.env;
 
+import java.io.IOException;
 import java.util.List;
 import java.util.Properties;
 
@@ -25,6 +26,7 @@ import org.junit.jupiter.api.Test;
 import org.springframework.boot.env.OriginTrackedPropertiesLoader.Document;
 import org.springframework.boot.origin.OriginTrackedValue;
 import org.springframework.boot.origin.TextResourceOrigin;
+import org.springframework.core.io.ByteArrayResource;
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.io.support.PropertiesLoaderUtils;
 
@@ -180,6 +182,34 @@ class OriginTrackedPropertiesLoaderTests {
 		assertThat(getLocation(value)).isEqualTo("32:1");
 	}
 
+	@Test
+	void loadWhenMultiDocumentWithoutWhitespaceLoadsMultiDoc() throws IOException {
+		String content = "a=a\n#---\nb=b";
+		List<Document> loaded = new OriginTrackedPropertiesLoader(new ByteArrayResource(content.getBytes())).load();
+		assertThat(loaded).hasSize(2);
+	}
+
+	@Test
+	void loadWhenMultiDocumentWithLeadingWhitespaceLoadsSingleDoc() throws IOException {
+		String content = "a=a\n \t#---\nb=b";
+		List<Document> loaded = new OriginTrackedPropertiesLoader(new ByteArrayResource(content.getBytes())).load();
+		assertThat(loaded).hasSize(1);
+	}
+
+	@Test
+	void loadWhenMultiDocumentWithTrailingWhitespaceLoadsMultiDoc() throws IOException {
+		String content = "a=a\n#--- \t \nb=b";
+		List<Document> loaded = new OriginTrackedPropertiesLoader(new ByteArrayResource(content.getBytes())).load();
+		assertThat(loaded).hasSize(2);
+	}
+
+	@Test
+	void loadWhenMultiDocumentWithTrailingCharsLoadsSingleDoc() throws IOException {
+		String content = "a=a\n#--- \tcomment\nb=b";
+		List<Document> loaded = new OriginTrackedPropertiesLoader(new ByteArrayResource(content.getBytes())).load();
+		assertThat(loaded).hasSize(1);
+	}
+
 	@Test
 	void getPropertyWithWhitespaceAfterKey() {
 		OriginTrackedValue value = getFromFirst("bar");