fix: incorrect multiline autoindent

org.eclipse.tm4e.languageconfiguration.tests/src/main/java/org/eclipse/tm4e/languageconfiguration/tests/TestIndentationRules.java

@@ -58,6 +58,18 @@ public void testIndentAdjustmentOnPaste() throws Exception {
 		text.insert("function bar() {\n}");
 		assertThat(text.getText()).isEqualTo("public class Foo {\n\tfunction bar() {\n\t}\n}");
 
+		// insert a code snippet with unindented first line and expect the snippet to be correctly indented
+		text.setText("public class Foo {\n\n}");
+		text.setSelection(19);
+		text.insert("function bar() {\n\t\t\n\t}");
+		assertThat(text.getText()).isEqualTo("public class Foo {\n\tfunction bar() {\n\t\t\n\t}\n}");
+
+		// insert an else code snippet with unindented first line after the if code snippet and expect the snippet to be correctly indented
+		text.setText("public class Foo {\n\tfunction foo() {\n\t\tif (cond) {\n\t\t} \n\t}\n}");
+		text.setSelection(55);
+		text.insert("else {\n\t\t}");
+		assertThat(text.getText()).isEqualTo("public class Foo {\n\tfunction foo() {\n\t\tif (cond) {\n\t\t} else {\n\t\t}\n\t}\n}");
+
 		// insert single line text and ensure the text is only indented in blank lines
 		text.setText("public class Foo {\n\n}");
 		text.setSelection(19);

org.eclipse.tm4e.languageconfiguration/src/main/java/org/eclipse/tm4e/languageconfiguration/internal/LanguageConfigurationAutoEditStrategy.java

@@ -163,17 +163,36 @@ && isFollowedBy(doc, command.offset, charPair.close))) {
 
 						final var newIndent = registry.getGoodIndentForLine(doc, lineIndex, contentType, IIndentConverter.of(cursorCfg));
 						if (newIndent != null) {
+							final var normalizedIndent = cursorCfg.normalizeIndentation(newIndent);
 							final var lineStartOffset = doc.getLineOffset(lineIndex);
-
-							// check if the content was pasted into a line while the cursor was not at the beginning of the line
-							// but inside or at the end of an existing line indentation
 							final var offsetInLine = command.offset - lineStartOffset;
-							if (offsetInLine > 0 && doc.get(lineStartOffset, offsetInLine).isBlank()) {
-								command.offset = lineStartOffset;
-								command.length += offsetInLine;
+							final int firstNewline = command.text.indexOf('\n');
+
+							if (firstNewline >= 0) {
+								final var firstLine = command.text.substring(0, firstNewline + 1);
+								// Re-indent lines after the first line
+								final var reindentedRest = TextUtils.replaceIndent(
+										command.text.substring(firstNewline + 1), cursorCfg.indentSize, normalizedIndent, false);
+
+								if (offsetInLine > 0 && !doc.get(lineStartOffset, offsetInLine).isBlank()) {
+									// Content was pasted midline after non-whitespace
+									// First pasted line continues existing content, don't replace indentation
+									command.text = firstLine + reindentedRest;
+								} else {
+									// Content was pasted at the start of the line, or preceded only by whitespace
+									// Replace any existing leading whitespace with the correct indent
+									if (offsetInLine > 0) {
+										command.offset = lineStartOffset;
+										command.length += offsetInLine;
+									}
+									command.text = normalizedIndent + firstLine.replaceFirst("^[ \\t]+", "") + reindentedRest;
+								}
+							} else {
+								// Single-line paste: straightforward indent replacement
+								command.text = TextUtils
+										.replaceIndent(command.text, cursorCfg.indentSize, normalizedIndent, false)
+										.toString();
 							}
-							command.text = TextUtils.replaceIndent(command.text, cursorCfg.indentSize,
-									cursorCfg.normalizeIndentation(newIndent), false).toString();
 							command.shiftsCaret = true;
 						}
 					}