Add linter task to phing for checking old PHP versions

README.md

@@ -90,5 +90,10 @@ Need Support?
     ``` sh
     vendor/bin/phing -f build/build.xml sniff
     ```
+6. (Optional) Lint the codebase with a specific PHP version to verify compatibility (requires Docker)
+
+    ``` sh
+    vendor/bin/phing -Dphpversion=5.3 -f build/build.xml lint
+    ```
 
 7. Send us a Pull Request

build/build.xml

@@ -22,4 +22,13 @@
         tests/"
       dir=".." checkreturn="true" passthru="true" />
   </target>
+  <target name="lint">
+      <exec command="PHING_PROPERTY=${phpversion};
+                     DEFAULT_PHP_VERSION=$(php -r 'echo phpversion();');
+                     export DOCKER_PHP_VERSION=${PHING_PROPERTY:-$DEFAULT_PHP_VERSION};
+                     find ./phpseclib -type f -name '*.php' -print0
+                        | xargs -0 -n1 -P$(nproc) ./build/docker-php.sh
+                        | (! grep -v '^No syntax errors detected' )"
+      dir=".." checkreturn="true" passthru="true" />
+  </target>
 </project>

build/docker-php.sh

@@ -0,0 +1,2 @@
+#! /usr/bin/env bash
+docker run -t --rm -v "$PWD:$PWD" -w $PWD php:$DOCKER_PHP_VERSION-cli php -l -n "$@"