feat: flag deprecated IPMasquerade= boolean values

A second user of the deprecation layer, found by scanning systemd.network(5):
the boolean forms of IPMasquerade= "are now deprecated. Please use one of the
values above" (ipv4/ipv6/both/no). The validator already enumerated the eleven
boolean aliases as accepted values; mark them deprecated so they get the weak
warning (truthy -> use "ipv4", falsy -> use "no"). Demonstrates the layer is
generic across grammars, not AF-specific.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Steve Ramage

src/main/kotlin/net/sjrx/intellij/plugins/systemdunitfiles/semanticdata/optionvalues/ai/ConfigParseIpMasqueradeOptionValue.kt

@@ -22,6 +22,17 @@ class ConfigParseIpMasqueradeOptionValue : SimpleGrammarOptionValues(
             "1", "yes", "y", "true", "t", "on",
             // Deprecated boolean false values (map to no)
             "0", "n", "false", "f", "off"
+        ).deprecating(
+            // systemd.network(5): the boolean forms "are now deprecated. Please use one of the
+            // values above" (ipv4/ipv6/both/no). Still accepted; the truthy forms map to ipv4.
+            buildMap {
+                for (t in listOf("1", "yes", "y", "true", "t", "on")) {
+                    put(t, "Boolean values for IPMasquerade= are deprecated; use \"ipv4\" (or \"ipv6\"/\"both\") instead.")
+                }
+                for (f in listOf("0", "n", "false", "f", "off")) {
+                    put(f, "Boolean values for IPMasquerade= are deprecated; use \"no\" instead.")
+                }
+            }
         ),
         EOF()
     )

src/test/kotlin/net/sjrx/intellij/plugins/systemdunitfiles/semanticdata/optionvalues/grammar/DeprecationsTest.kt

@@ -1,6 +1,7 @@
 package net.sjrx.intellij.plugins.systemdunitfiles.semanticdata.optionvalues.grammar
 
 import net.sjrx.intellij.plugins.systemdunitfiles.semanticdata.optionvalues.ai.ConfigParseAddressFamiliesOptionValue
+import net.sjrx.intellij.plugins.systemdunitfiles.semanticdata.optionvalues.ai.ConfigParseIpMasqueradeOptionValue
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
 import org.junit.Test
@@ -31,4 +32,15 @@ class DeprecationsTest {
     // No full parse -> nothing (the InvalidValue inspection handles the error instead).
     assertTrue(grammar.deprecatedTokens("AF_DECnet AF_BOGUS").isEmpty())
   }
+
+  @Test
+  fun testIpMasqueradeBooleanValuesAreDeprecated() {
+    // A second, unrelated user of the same layer: the legacy boolean forms of IPMasquerade= are
+    // accepted but deprecated in favour of ipv4/ipv6/both/no.
+    val ipMasquerade = ConfigParseIpMasqueradeOptionValue().combinator
+    assertTrue(ipMasquerade.deprecatedTokens("true").single().message.contains("ipv4"))
+    assertTrue(ipMasquerade.deprecatedTokens("off").single().message.contains("no"))
+    assertTrue(ipMasquerade.deprecatedTokens("ipv4").isEmpty())
+    assertTrue(ipMasquerade.deprecatedTokens("both").isEmpty())
+  }
 }