Update jffi dependency scope to 'provided'

docs/docs/experimental/redline.md

@@ -96,7 +96,28 @@ versions use `redline-runner-jffi-experimental`, which needs only Java 11:
 </dependency>
 ```
 
-If both are present, the Panama runner is used wherever the JDK supports it.
+The jffi runner does not bring in [jffi](https://github.com/jnr/jffi) itself, so its version can
+follow the rest of your application. Add it next to the runner, together with its native
+libraries:
+
+```xml
+<dependency>
+  <groupId>com.github.jnr</groupId>
+  <artifactId>jffi</artifactId>
+  <version>${jffi.version}</version>
+</dependency>
+<dependency>
+  <groupId>com.github.jnr</groupId>
+  <artifactId>jffi</artifactId>
+  <version>${jffi.version}</version>
+  <classifier>native</classifier>
+</dependency>
+```
+
+Without them, `builder()` fails with `NoClassDefFoundError: com/kenai/jffi/MemoryIO` instead of
+falling back.
+
+If both runners are present, the Panama runner is used wherever the JDK supports it.
 
 Your module is then used exactly as it would be without redline:
 
@@ -110,7 +131,8 @@ try (var instance = MyModule.builder().build()) {
 
 When native code cannot be used, `builder()` falls back to the bytecode produced by the
 [Build Time Compiler](../execution/build-time-compiler.md), which is always generated alongside it.
-This happens on platforms outside the table above, or when no runner is on the classpath.
+This happens on platforms outside the table above, or when no runner is on the classpath. A jffi
+runner without jffi is an error, not a fallback.
 
 Your module keeps working either way, so the fallback is silent. To check which one you got:
 

redline/it/src/it/redline-e2e/pom.xml

@@ -8,8 +8,19 @@
   <packaging>jar</packaging>
 
   <dependencies>
-    <!-- The only dependency a consumer needs. It brings in redline-api (used by
-         the generated builder), runtime and wasm transitively. -->
+    <!-- What a consumer needs: jffi, which the runner declares as provided, and the
+         runner, which brings in redline-api, runtime and wasm transitively. -->
+    <dependency>
+      <groupId>com.github.jnr</groupId>
+      <artifactId>jffi</artifactId>
+      <version>@jffi.version@</version>
+    </dependency>
+    <dependency>
+      <groupId>com.github.jnr</groupId>
+      <artifactId>jffi</artifactId>
+      <version>@jffi.version@</version>
+      <classifier>native</classifier>
+    </dependency>
     <dependency>
       <groupId>run.endive</groupId>
       <artifactId>redline-runner-jffi-experimental</artifactId>

redline/runner-jffi-tests/pom.xml

@@ -18,6 +18,17 @@
   </properties>
 
   <dependencies>
+    <dependency>
+      <groupId>com.github.jnr</groupId>
+      <artifactId>jffi</artifactId>
+      <scope>runtime</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.github.jnr</groupId>
+      <artifactId>jffi</artifactId>
+      <classifier>native</classifier>
+      <scope>runtime</scope>
+    </dependency>
     <dependency>
       <groupId>org.junit.jupiter</groupId>
       <artifactId>junit-jupiter-api</artifactId>

redline/runner-jffi/pom.xml

@@ -14,10 +14,6 @@
   <description>Native code execution via JFFI (Java 11+)</description>
 
   <dependencies>
-    <dependency>
-      <groupId>com.github.jnr</groupId>
-      <artifactId>jffi</artifactId>
-    </dependency>
     <dependency>
       <groupId>run.endive</groupId>
       <artifactId>redline-api-experimental</artifactId>
@@ -37,8 +33,7 @@
     <dependency>
       <groupId>com.github.jnr</groupId>
       <artifactId>jffi</artifactId>
-      <classifier>native</classifier>
-      <scope>runtime</scope>
+      <scope>provided</scope>
     </dependency>
   </dependencies>
 </project>