Support escaping property placeholders with backslash (#6817)

* Support escaping property placeholders in recipe YAML

When recipe YAML contains Maven property references like ${java.version}
in parameter values, the YamlResourceLoader resolves them as property
placeholders at load time. This prevents users from passing literal
${...} references through to recipe parameters.

Add escape support: doubling the first character of the placeholder
prefix (e.g., writing $${java.version} for the ${ prefix) produces
a literal ${java.version} in the resolved output.

Fixes moderneinc/customer-requests#1874

* Support escaping property placeholders in recipe YAML

When recipe YAML contains Maven property references like ${java.version}
in parameter values, the YamlResourceLoader resolves them as property
placeholders at load time. This prevents users from passing literal
${...} references through to recipe parameters.

Add escape support: a backslash before the placeholder prefix (e.g.,
writing \${java.version} for the ${ prefix) produces a literal
${java.version} in the resolved output.

Fixes moderneinc/customer-requests#1874

* Update configuration description and add regression tests

Document the \${...} escape syntax in the ChangePluginConfiguration
@option description so users know how to pass literal Maven property
references.

Add regression tests to ensure existing behavior is preserved:
- Unresolved placeholders are left as-is
- Normal resolution still works
- Backslashes not before a placeholder prefix are preserved

* Add javadoc to replacePlaceholders methods

* Polish

* Regenerate recipes.csv for updated docs; remove duplicates

---------

Co-authored-by: Tim te Beek <tim@moderne.io>

Author: MBoegers

rewrite-core/src/main/java/org/openrewrite/internal/PropertyPlaceholderHelper.java

@@ -84,12 +84,31 @@ public List<String> getPlaceholders(@Nullable String value) {
         return placeholders;
     }
 
+    /**
+     * Replace placeholders in the given value, resolving each against the supplied properties.
+     * A backslash before the placeholder prefix (e.g. {@code \${...}}) escapes it as a literal.
+     */
     public String replacePlaceholders(String value, final Properties properties) {
         return replacePlaceholders(value, properties::getProperty);
     }
 
+    /**
+     * Replace placeholders in the given value, resolving each via {@code placeholderResolver}.
+     * A backslash before the placeholder prefix (e.g. {@code \${...}}) escapes it as a literal.
+     */
     public String replacePlaceholders(String value, Function<String, @Nullable String> placeholderResolver) {
-        return parseStringValue(value, placeholderResolver, null);
+        // Support escaping: a backslash before the placeholder prefix produces a literal
+        // prefix. E.g., for prefix "${", writing "\${" produces literal "${".
+        String escapePrefix = "\\" + placeholderPrefix;
+        boolean hasEscaped = value.contains(escapePrefix);
+        if (hasEscaped) {
+            value = value.replace(escapePrefix, "\u0000\u0001\u0002");
+        }
+        String result = parseStringValue(value, placeholderResolver, null);
+        if (hasEscaped) {
+            result = result.replace("\u0000\u0001\u0002", placeholderPrefix);
+        }
+        return result;
     }
 
     protected String parseStringValue(String value, Function<String, @Nullable String> placeholderResolver,

rewrite-core/src/test/java/org/openrewrite/internal/PropertyPlaceholderHelperTest.java

@@ -88,6 +88,52 @@ void withValueSeparatorAndValueReplacement() {
         assertThat(s).isEqualTo("hi jon");
     }
 
+    @Test
+    void escapedPlaceholder() {
+        var helper = new PropertyPlaceholderHelper("${", "}", null);
+        var s = helper.replacePlaceholders("\\${java.version}", k -> "should-not-resolve");
+        assertThat(s).isEqualTo("${java.version}");
+    }
+
+    @Test
+    void escapedPlaceholderWithOtherPrefix() {
+        var helper = new PropertyPlaceholderHelper("%%{", "}", null);
+        var s = helper.replacePlaceholders("\\%%{k1}", k -> "should-not-resolve");
+        assertThat(s).isEqualTo("%%{k1}");
+    }
+
+    @Test
+    void mixedEscapedAndResolvedPlaceholders() {
+        var helper = new PropertyPlaceholderHelper("${", "}", null);
+        var s = helper.replacePlaceholders("${greeting} \\${java.version}", k -> "greeting".equals(k) ? "hello" : null);
+        assertThat(s).isEqualTo("hello ${java.version}");
+    }
+
+    @Test
+    void unresolvedPlaceholderLeftAsIs() {
+        var helper = new PropertyPlaceholderHelper("${", "}", null);
+        var s = helper.replacePlaceholders("${unresolved}", k -> null);
+        assertThat(s).isEqualTo("${unresolved}");
+    }
+
+    @Test
+    void normalResolutionStillWorks() {
+        var helper = new PropertyPlaceholderHelper("${", "}", null);
+        var s = helper.replacePlaceholders("${greeting} ${name}", k -> switch (k) {
+            case "greeting" -> "hello";
+            case "name" -> "world";
+            default -> null;
+        });
+        assertThat(s).isEqualTo("hello world");
+    }
+
+    @Test
+    void backslashNotBeforePrefixIsPreserved() {
+        var helper = new PropertyPlaceholderHelper("${", "}", null);
+        var s = helper.replacePlaceholders("path\\to\\file", k -> null);
+        assertThat(s).isEqualTo("path\\to\\file");
+    }
+
     @Test
     void withValueSeparatorAndNullReplacement() {
         var helper = new PropertyPlaceholderHelper("%%{", "}", ",");

rewrite-maven/src/main/java/org/openrewrite/maven/ChangePluginConfiguration.java

@@ -50,7 +50,10 @@ public class ChangePluginConfiguration extends Recipe {
     @Option(displayName = "Configuration",
             description = "Plugin configuration provided as raw XML overriding any existing configuration. " +
                           "Configuration inside `<executions>` blocks will not be altered. " +
-                          "Supplying `null` will remove any existing configuration.",
+                          "Supplying `null` will remove any existing configuration. " +
+                          "To include a literal `${...}` property reference in the configuration " +
+                          "(e.g. a Maven property like `${java.version}`), escape it as `\\${...}` " +
+                          "in your recipe YAML to prevent it from being resolved as a recipe placeholder.",
             example = "<foo>bar</foo>",
             required = false)
     @Nullable