JsonPath runtime compilation

json-java21-jsonpath/AGENTS.md

@@ -5,13 +5,43 @@ This file is for contributor/agent operational notes. Read `json-java21-jsonpath
 - User docs MUST recommend only `./mvnw`.
 - The `$(command -v mvnd || command -v mvn || command -v ./mvnw)` wrapper is for local developer speed only; do not put it in user-facing docs.
 
-Stable code entry points:
-- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPath.java`
-- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathParser.java`
-- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathAst.java`
-- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathParseException.java`
-- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathStreams.java`
-
-When changing syntax/behavior:
-- Update `JsonPathAst` + `JsonPathParser` + `JsonPath` together.
+## Architecture
+
+JsonPath is a sealed interface with two implementations:
+- `JsonPathInterpreted`: AST-walking interpreter (default from `JsonPath.parse()`)
+- `JsonPathCompiled`: Bytecode-compiled version (from `JsonPath.compile()`)
+
+The compilation flow:
+1. `JsonPath.parse()` -> `JsonPathInterpreted` (fast parsing, AST-based evaluation)
+2. `JsonPath.compile()` -> `JsonPathCompiled` (generates Java source, compiles with JDK ToolProvider)
+
+## Stable Code Entry Points
+
+- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPath.java` - Public sealed interface
+- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathParser.java` - Parses expressions to AST
+- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathAst.java` - AST node definitions
+- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathInterpreted.java` - AST-walking evaluator
+- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathCompiler.java` - Code generator and compiler
+- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathCompiled.java` - Compiled executor wrapper
+- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathExecutor.java` - Public interface for generated executors
+- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathHelpers.java` - Helpers for generated code
+- `json-java21-jsonpath/src/main/java/json/java21/jsonpath/JsonPathStreams.java` - Stream processing utilities
+
+## When Changing Syntax/Behavior
+
+- Update `JsonPathAst` + `JsonPathParser` + `JsonPathInterpreted` together.
+- Update `JsonPathCompiler` code generation to match any AST changes.
 - Add parser + evaluation tests; new tests should extend `JsonPathLoggingConfig`.
+- Add compiler tests in `JsonPathCompilerTest` to verify compiled and interpreted produce identical results.
+
+## Code Generation Notes
+
+The `JsonPathCompiler` generates Java source code that:
+- Imports from `jdk.sandbox.java.util.json.*` and `json.java21.jsonpath.*`
+- Implements `JsonPathExecutor` functional interface
+- Uses `JsonPathHelpers` for complex operations (recursive descent, comparisons)
+- Is compiled in-memory using `javax.tools.ToolProvider`
+
+When adding new AST node types:
+1. Add the case to `generateSegmentEvaluation()` in `JsonPathCompiler`
+2. Consider if a helper method in `JsonPathHelpers` would simplify the generated code

json-java21-jsonpath/README.md

@@ -60,6 +60,57 @@ This implementation follows Goessner-style JSONPath operators, including:
 - `[?(@.prop)]` and `[?(@.prop op value)]` basic filters
 - `[(@.length-1)]` limited script support
 
+## Runtime Compilation (Performance Optimization)
+
+For performance-critical code paths, you can compile a parsed JsonPath to bytecode:
+
+```java
+// Parse once, compile for best performance
+JsonPath compiled = JsonPath.compile(JsonPath.parse("$.store.book[*].author"));
+
+// Reuse the compiled path for many documents
+for (JsonValue doc : documents) {
+    List<JsonValue> results = compiled.query(doc);
+    // process results...
+}
+```
+
+### How It Works
+
+The `JsonPath.compile()` method:
+1. Takes a parsed (interpreted) JsonPath
+2. Generates optimized Java source code
+3. Compiles it to bytecode using the JDK compiler API (`javax.tools.ToolProvider`)
+4. Returns a compiled JsonPath that executes as native bytecode
+
+### When to Use Compilation
+
+- **Hot paths**: Use `compile()` when the same path will be executed many times
+- **One-off queries**: Use `parse()` directly for single-use paths (compilation overhead isn't worth it)
+- **JRE environments**: Compilation requires a JDK; if unavailable, use interpreted paths
+
+### Compilation is Idempotent
+
+Calling `compile()` on an already-compiled path returns the same instance:
+
+```java
+JsonPath interpreted = JsonPath.parse("$.store");
+JsonPath compiled = JsonPath.compile(interpreted);
+JsonPath sameCompiled = JsonPath.compile(compiled); // Returns same instance
+
+// Check if a path is compiled
+boolean isCompiled = compiled.isCompiled();
+boolean isInterpreted = interpreted.isInterpreted();
+```
+
+### Supported Features in Compiled Mode
+
+All JsonPath features are supported in compiled mode:
+- Property access, array indices, slices, wildcards
+- Recursive descent (`$..property`)
+- Filters with comparisons and logical operators
+- Unions and limited script expressions (e.g., `[(@.length-1)]`)
+
 ## Stream-Based Functions (Aggregations)
 
 Some JsonPath implementations include aggregation functions such as `$.numbers.avg()`.