Initial implementation of Java Preprocessing Library (Maven)

README.md

@@ -1,2 +1,132 @@
-# java-preprocessing-lib
-Trying to create a library to somehow preprocess the java code using directives.
+# Java Preprocessing Library
+
+A lightweight Java library and Maven plugin that brings C++ style preprocessor directives (`#if`, `#ifdef`, etc.) to Java. This allows for conditional compilation based on build-time symbols, enabling feature toggles, multi-version builds, and platform-specific code generation.
+
+## Features
+
+*   **Standard Directives**: Support for `#if`, `#ifdef`, `#ifndef`, `#else`, `#endif`.
+*   **Expression Evaluation**: Support for complex boolean expressions in `#if` directives (e.g., `#if DEBUG && VERSION > 1`).
+*   **Maven Plugin**: Seamless integration into the Maven build lifecycle (`generate-sources`).
+*   **Zero Runtime Dependencies**: The preprocessor runs at build time; the generated code is pure Java with no extra runtime requirements.
+
+## Installation
+
+Currently, you need to build and install the library locally:
+
+```bash
+git clone https://github.com/your-repo/java-preprocessing-lib.git
+cd java-preprocessing-lib
+mvn install
+```
+
+## Usage
+
+### Maven Configuration
+
+Add the `preprocessor-maven-plugin` to your `pom.xml`. It should be configured to run during the `generate-sources` phase.
+
+**Note**: To use the preprocessor effectively, it is recommended to keep your source files with directives in a separate directory (e.g., `src/main/preprocess`) to prevent the standard Java compiler from trying to compile the unprocessed files.
+
+```xml
+<build>
+    <plugins>
+        <plugin>
+            <groupId>com.github.javapreprocessor</groupId>
+            <artifactId>preprocessor-maven-plugin</artifactId>
+            <version>1.0.0-SNAPSHOT</version>
+            <executions>
+                <execution>
+                    <id>preprocess-sources</id>
+                    <phase>generate-sources</phase>
+                    <goals>
+                        <goal>process</goal>
+                    </goals>
+                    <configuration>
+                        <!-- Directory containing source files with directives -->
+                        <sourceDirectory>${project.basedir}/src/main/preprocess</sourceDirectory>
+
+                        <!-- Define symbols for conditional compilation -->
+                        <symbols>
+                            <DEBUG>true</DEBUG>
+                            <VERSION>2</VERSION>
+                            <FEATURE_X>false</FEATURE_X>
+                        </symbols>
+                    </configuration>
+                </execution>
+            </executions>
+        </plugin>
+    </plugins>
+</build>
+```
+
+### Supported Directives
+
+#### `#ifdef` / `#ifndef`
+Checks if a symbol is defined (or not defined).
+
+```java
+#ifdef DEBUG
+    System.out.println("Debug logging enabled");
+#endif
+
+#ifndef PRODUCTION
+    // Test helper code
+#endif
+```
+
+#### `#if` / `#else` / `#endif`
+Evaluates a boolean expression. Supports `&&`, `||`, `!`, `>`, `<`, `>=`, `<=`, `==`, `!=`, and `defined()`.
+
+```java
+#if VERSION > 1 && defined(FEATURE_NEW_UI)
+    renderNewUI();
+#else
+    renderClassicUI();
+#endif
+```
+
+#### `#else`
+Alternative branch for `#if`, `#ifdef`, or `#ifndef`.
+
+## Example
+
+**Input (`src/main/preprocess/com/example/App.java`):**
+```java
+package com.example;
+
+public class App {
+    public static void main(String[] args) {
+        #if DEBUG
+        System.out.println("Debugging...");
+        #endif
+
+        System.out.println("Running App");
+    }
+}
+```
+
+**Configuration (pom.xml):**
+```xml
+<symbols>
+    <DEBUG>true</DEBUG>
+</symbols>
+```
+
+**Generated Output (`target/generated-sources/preprocessed/com/example/App.java`):**
+```java
+package com.example;
+
+public class App {
+    public static void main(String[] args) {
+
+        System.out.println("Debugging...");
+
+
+        System.out.println("Running App");
+    }
+}
+```
+
+## License
+
+[MIT License](LICENSE)

example-usage/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>com.example</groupId>
+  <artifactId>example-usage</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>com.github.javapreprocessor</groupId>
+        <artifactId>preprocessor-maven-plugin</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <executions>
+          <execution>
+            <id>preprocess-sources</id>
+            <phase>generate-sources</phase>
+            <goals>
+              <goal>process</goal>
+            </goals>
+            <configuration>
+              <sourceDirectory>${project.basedir}/src/main/preprocess</sourceDirectory>
+              <symbols>
+                <DEBUG>true</DEBUG>
+                <VERSION>2</VERSION>
+              </symbols>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+
+      <!-- Configure compiler to look at generated sources -->
+      <!-- Actually, the plugin adds the source root automatically. But we need to make sure standard compiler doesn't complain about missing methods in original source if we were modifying in place. 
+           But here we are generating to target/generated-sources. 
+           Wait, if we have src/main/java/App.java, and it has #ifdef, it's not valid Java. 
+           So standard compiler will fail if it tries to compile src/main/java/App.java.
+
+           We need to tell Maven Compiler Plugin to IGNORE src/main/java?
+           Or, we should put our *template* sources in a different directory, e.g. src/main/java-templates?
+           The plugin defaults to src/main/java.
+
+           If we use src/main/java as input, we must ensure the compiler doesn't try to compile it directly.
+           Or we just assume the user puts valid Java code "around" the directives?
+           No, directives start with #, which is illegal in Java.
+
+           So users CANNOT keep their source in src/main/java if they want to use standard `compile`.
+           They should put it in `src/main/preprocessed` or similar.
+
+           Let's change the default source directory in the Mojo, or override it here.
+           Let's use `src/main/preprocess` for this example.
+      -->
+    </plugins>
+  </build>
+
+  <properties>
+    <maven.compiler.source>1.8</maven.compiler.source>
+    <maven.compiler.target>1.8</maven.compiler.target>
+  </properties>
+</project>

example-usage/src/main/preprocess/com/example/App.java

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+package com.example;
+
+public class App {
+    public static void main(String[] args) {
+        System.out.println("Hello World!");
+
+        #if DEBUG
+        System.out.println("Debug mode enabled");
+        #endif
+
+        #if VERSION > 1
+        System.out.println("Version is greater than 1");
+        #endif
+
+        #if VERSION < 1
+        System.out.println("Version is less than 1");
+        #endif
+    }
+}

example-usage/target/generated-sources/preprocessed/com/example/App.java

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+package com.example;
+
+public class App {
+    public static void main(String[] args) {
+        System.out.println("Hello World!");
+
+
+        System.out.println("Debug mode enabled");
+
+
+
+        System.out.println("Version is greater than 1");
+
+
+
+
+
+    }
+}

example-usage/target/maven-status/maven-compiler-plugin/compile/default-compile/createdFiles.lst

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+com/example/App.class

example-usage/target/maven-status/maven-compiler-plugin/compile/default-compile/inputFiles.lst

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+/home/tejas-warake/Desktop/open-source/java-preprocessing-lib/example-usage/target/generated-sources/preprocessed/com/example/App.java

pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>com.github.javapreprocessor</groupId>
+  <artifactId>java-preprocessing-lib-parent</artifactId>
+  <packaging>pom</packaging>
+  <version>1.0.0-SNAPSHOT</version>
+  <name>Java Preprocessing Library Parent</name>
+
+  <modules>
+    <module>preprocessor-core</module>
+    <module>preprocessor-maven-plugin</module>
+  </modules>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.source>1.8</maven.compiler.source>
+    <maven.compiler.target>1.8</maven.compiler.target>
+  </properties>
+
+  <dependencyManagement>
+    <dependencies>
+      <dependency>
+        <groupId>junit</groupId>
+        <artifactId>junit</artifactId>
+        <version>4.13.2</version>
+        <scope>test</scope>
+      </dependency>
+    </dependencies>
+  </dependencyManagement>
+</project>

preprocessor-core/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.github.javapreprocessor</groupId>
+    <artifactId>java-preprocessing-lib-parent</artifactId>
+    <version>1.0.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>preprocessor-core</artifactId>
+  <packaging>jar</packaging>
+  <name>Preprocessor Core</name>
+
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>