Handle single quotes in ReplaceStringBuilderWithString (#775)

Author: timtebeek

src/main/java/org/openrewrite/staticanalysis/ReplaceStringBuilderWithString.java

@@ -101,6 +101,21 @@ private J.Literal toStringLiteral(J.Literal input) {
                     return input;
                 }
 
+                // Handle character literals by stripping single quotes and wrapping in double quotes
+                if (input.getType() == JavaType.Primitive.Char) {
+                    String charSource = input.getValueSource();
+                    if (charSource != null && charSource.length() >= 2 &&
+                        charSource.startsWith("'") && charSource.endsWith("'")) {
+                        String charContent = charSource.substring(1, charSource.length() - 1);
+                        String stringValue = input.getValue() != null ? String.valueOf(input.getValue()) : charContent;
+                        String valueSource = "\"" + charContent + "\"";
+                        return input
+                                .withType(JavaType.Primitive.String)
+                                .withValue(stringValue)
+                                .withValueSource(valueSource);
+                    }
+                }
+
                 String value = input.getValueSource();
                 return new J.Literal(randomId(), Space.EMPTY, Markers.EMPTY, value,
                         "\"" + value + "\"", null, JavaType.Primitive.String);

src/test/java/org/openrewrite/staticanalysis/ReplaceStringBuilderWithStringTest.java

@@ -390,4 +390,35 @@ void print(String str, String str2) {
           )
         );
     }
+
+    @Test
+    void characterLiterals() {
+        rewriteRun(
+          //language=java
+          java(
+            """
+              class A {
+                  String track(Object consumer) {
+                      return "tracked";
+                  }
+
+                  String method(String text, Object consumer) {
+                      return new StringBuilder(50).append('[').append(track(consumer)).append("]: ").append(text).toString();
+                  }
+              }
+              """,
+            """
+              class A {
+                  String track(Object consumer) {
+                      return "tracked";
+                  }
+
+                  String method(String text, Object consumer) {
+                      return "[" + track(consumer) + "]: " + text;
+                  }
+              }
+              """
+          )
+        );
+    }
 }