refactor: Replace reflection-based codepage detection with TerminalProvider method

Add getConsoleCodepage() default method to TerminalProvider interface,
with overrides in JNI and FFM providers that call Kernel32.GetConsoleOutputCP().
This eliminates the fragile reflection-based approach in TerminalBuilder that
coupled it to provider internals.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: gnodet

terminal-ffm/src/main/java/org/jline/terminal/impl/ffm/FfmTerminalProvider.java

@@ -43,6 +43,14 @@ public String name() {
         return TerminalBuilder.PROP_PROVIDER_FFM;
     }
 
+    @Override
+    public int getConsoleCodepage() {
+        if (OSUtils.IS_WINDOWS) {
+            return Kernel32.GetConsoleOutputCP();
+        }
+        return -1;
+    }
+
     @Override
     public Terminal sysTerminal(
             String name,

terminal-jni/src/main/java/org/jline/terminal/impl/jni/JniTerminalProvider.java

@@ -97,6 +97,14 @@ public String name() {
         return TerminalBuilder.PROP_PROVIDER_JNI;
     }
 
+    @Override
+    public int getConsoleCodepage() {
+        if (OSUtils.IS_WINDOWS) {
+            return org.jline.nativ.Kernel32.GetConsoleOutputCP();
+        }
+        return -1;
+    }
+
     public Pty current(SystemStream systemStream) throws IOException {
         String osName = System.getProperty("os.name");
         if (osName.startsWith("Linux")) {

terminal/src/main/java/org/jline/terminal/TerminalBuilder.java

@@ -732,10 +732,6 @@ private Terminal doBuild() throws IOException {
         if (name == null) {
             name = "JLine terminal";
         }
-        Charset encoding = computeEncoding();
-        Charset stdinEncoding = computeStdinEncoding();
-        Charset stdoutEncoding = computeStdoutEncoding();
-        Charset stderrEncoding = computeStderrEncoding();
         String type = computeType();
 
         String provider = this.provider;
@@ -752,6 +748,20 @@ private Terminal doBuild() throws IOException {
         }
         IllegalStateException exception = new IllegalStateException("Unable to create a terminal");
         List<TerminalProvider> providers = getProviders(provider, exception);
+
+        // Query providers for console codepage (Windows auto-detection)
+        int consoleCodepage = -1;
+        for (TerminalProvider prov : providers) {
+            consoleCodepage = prov.getConsoleCodepage();
+            if (consoleCodepage >= 0) {
+                break;
+            }
+        }
+
+        Charset encoding = computeEncoding(consoleCodepage);
+        Charset stdinEncoding = computeStdinEncoding();
+        Charset stdoutEncoding = computeStdoutEncoding();
+        Charset stderrEncoding = computeStderrEncoding();
         Terminal terminal = null;
         if ((system != null && system) || (system == null && in == null && out == null)) {
             if (system != null
@@ -989,6 +999,10 @@ public String computeType() {
     }
 
     public Charset computeEncoding() {
+        return computeEncoding(-1);
+    }
+
+    Charset computeEncoding(int consoleCodepage) {
         Charset encoding = this.encoding;
         if (encoding == null) {
             String charsetName = System.getProperty(PROP_ENCODING);
@@ -1007,7 +1021,7 @@ public Charset computeEncoding() {
             // Auto-detect Windows console codepage if not explicitly set
             // Only auto-detect when codepage == 0 (unset), not -1 (explicitly set to force UTF-8)
             if (codepage == 0 && OSUtils.IS_WINDOWS && !OSUtils.IS_CYGWIN && !OSUtils.IS_MSYSTEM) {
-                codepage = getConsoleCodepage();
+                codepage = consoleCodepage;
             }
             if (codepage > 0) {
                 encoding = getCodepageCharset(codepage);
@@ -1171,39 +1185,6 @@ private static <S> S load(Class<S> clazz) {
 
     private static final int UTF8_CODE_PAGE = 65001;
 
-    /**
-     * Auto-detect the Windows console output codepage using GetConsoleOutputCP().
-     * Uses reflection to avoid hard dependency on native provider modules.
-     *
-     * @return the detected codepage (positive integer), 0 if detection fails or API returns 0,
-     *         or -1 to indicate no native provider is available
-     */
-    private static int getConsoleCodepage() {
-        try {
-            // Try JNI provider's Kernel32 first
-            Class<?> kernel32Class = Class.forName("org.jline.nativ.Kernel32");
-            java.lang.reflect.Method method = kernel32Class.getMethod("GetConsoleOutputCP");
-            int codepage = (Integer) method.invoke(null);
-            // GetConsoleOutputCP returns 0 on failure - treat as detection failure
-            return codepage > 0 ? codepage : 0;
-        } catch (ClassNotFoundException | NoSuchMethodException e) {
-            // JNI provider not available, try FFM provider
-            try {
-                Class<?> kernel32Class = Class.forName("org.jline.terminal.impl.ffm.Kernel32");
-                java.lang.reflect.Method method = kernel32Class.getMethod("GetConsoleOutputCP");
-                int codepage = (Integer) method.invoke(null);
-                // GetConsoleOutputCP returns 0 on failure - treat as detection failure
-                return codepage > 0 ? codepage : 0;
-            } catch (Throwable ex) {
-                // FFM provider not available or reflection failed, return -1
-                return -1;
-            }
-        } catch (Throwable e) {
-            // Reflection failed (including ExceptionInInitializerError, LinkageError), return -1
-            return -1;
-        }
-    }
-
     private static Charset getCodepageCharset(int codepage) {
         // http://docs.oracle.com/javase/6/docs/technotes/guides/intl/encoding.doc.html
         if (codepage == UTF8_CODE_PAGE) {

terminal/src/main/java/org/jline/terminal/spi/TerminalProvider.java

@@ -182,6 +182,21 @@ Terminal newTerminal(
      */
     int systemStreamWidth(SystemStream stream);
 
+    /**
+     * Returns the Windows console output codepage.
+     *
+     * <p>
+     * On Windows, this method returns the console output codepage (equivalent to
+     * {@code GetConsoleOutputCP()}). On non-Windows platforms, or if the codepage
+     * cannot be determined, this method returns {@code -1}.
+     * </p>
+     *
+     * @return the console output codepage, or {@code -1} if not available
+     */
+    default int getConsoleCodepage() {
+        return -1;
+    }
+
     /**
      * Loads a terminal provider with the specified name.
      *