2 files changed, 77 insertions, 21 deletions

diff --git a/java/com/google/turbine/binder/Processing.java b/java/com/google/turbine/binder/Processing.java
index 7b19575..aad88a4 100644
--- a/java/com/google/turbine/binder/Processing.java
+++ b/java/com/google/turbine/binder/Processing.java
@@ -28,6 +28,7 @@ import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSetMultimap;
 import com.google.common.collect.Sets;
+import com.google.common.primitives.Ints;
 import com.google.turbine.binder.Binder.BindingResult;
 import com.google.turbine.binder.Binder.Statistics;
 import com.google.turbine.binder.bound.SourceTypeBoundClass;
@@ -439,28 +440,10 @@ public class Processing {
       String option = it.next();
       switch (option) {
         case "-source":
-          if (it.hasNext()) {
-            String value = it.next();
-            switch (value) {
-              case "5":
-              case "1.5":
-                sourceVersion = SourceVersion.RELEASE_5;
-                break;
-              case "6":
-              case "1.6":
-                sourceVersion = SourceVersion.RELEASE_6;
-                break;
-              case "7":
-              case "1.7":
-                sourceVersion = SourceVersion.RELEASE_7;
-                break;
-              case "8":
-                sourceVersion = SourceVersion.RELEASE_8;
-                break;
-              default:
-                break;
-            }
+          if (!it.hasNext()) {
+            throw new IllegalArgumentException("-source requires an argument");
           }
+          sourceVersion = parseSourceVersion(it.next());
           break;
         default:
           break;
@@ -469,6 +452,34 @@ public class Processing {
     return sourceVersion;
   }
 
+  private static SourceVersion parseSourceVersion(String value) {
+    boolean hasPrefix = value.startsWith("1.");
+    Integer version = Ints.tryParse(hasPrefix ? value.substring("1.".length()) : value);
+    if (!isValidSourceVersion(version, hasPrefix)) {
+      throw new IllegalArgumentException("invalid -source version: " + value);
+    }
+    try {
+      return SourceVersion.valueOf("RELEASE_" + version);
+    } catch (IllegalArgumentException unused) {
+      throw new IllegalArgumentException("invalid -source version: " + value);
+    }
+  }
+
+  private static boolean isValidSourceVersion(Integer version, boolean hasPrefix) {
+    if (version == null) {
+      return false;
+    }
+    if (version < 5) {
+      // the earliest source version supported by JDK 8 is Java 5
+      return false;
+    }
+    if (hasPrefix && version > 10) {
+      // javac supports legacy `1.*` version numbers for source versions up to Java 10
+      return false;
+    }
+    return true;
+  }
+
   private static URL[] toUrls(ImmutableList<String> processorPath) throws MalformedURLException {
     URL[] urls = new URL[processorPath.size()];
     int i = 0;
diff --git a/javatests/com/google/turbine/binder/ProcessingTest.java b/javatests/com/google/turbine/binder/ProcessingTest.java
index 75203e9..b7091e8 100644
--- a/javatests/com/google/turbine/binder/ProcessingTest.java
+++ b/javatests/com/google/turbine/binder/ProcessingTest.java
@@ -17,6 +17,7 @@
 package com.google.turbine.binder;
 
 import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertThrows;
 
 import com.google.common.collect.ImmutableList;
 import javax.lang.model.SourceVersion;
@@ -35,4 +36,48 @@ public class ProcessingTest {
     assertThat(Processing.parseSourceVersion(ImmutableList.of("-source", "8", "-source", "7")))
         .isEqualTo(SourceVersion.RELEASE_7);
   }
+
+  @Test
+  public void withPrefix() {
+    assertThat(Processing.parseSourceVersion(ImmutableList.of("-source", "1.7")))
+        .isEqualTo(SourceVersion.RELEASE_7);
+    assertThat(Processing.parseSourceVersion(ImmutableList.of("-source", "1.8")))
+        .isEqualTo(SourceVersion.RELEASE_8);
+  }
+
+  @Test
+  public void invalidPrefix() {
+    IllegalArgumentException expected =
+        assertThrows(
+            IllegalArgumentException.class,
+            () -> Processing.parseSourceVersion(ImmutableList.of("-source", "1.11")));
+    assertThat(expected).hasMessageThat().contains("invalid -source version: 1.11");
+  }
+
+  @Test
+  public void latestSupported() {
+    String latest = SourceVersion.latestSupported().toString();
+    assertThat(latest).startsWith("RELEASE_");
+    latest = latest.substring("RELEASE_".length());
+    assertThat(Processing.parseSourceVersion(ImmutableList.of("-source", latest)))
+        .isEqualTo(SourceVersion.latestSupported());
+  }
+
+  @Test
+  public void missingArgument() {
+    IllegalArgumentException expected =
+        assertThrows(
+            IllegalArgumentException.class,
+            () -> Processing.parseSourceVersion(ImmutableList.of("-source")));
+    assertThat(expected).hasMessageThat().contains("-source requires an argument");
+  }
+
+  @Test
+  public void invalidSourceVersion() {
+    IllegalArgumentException expected =
+        assertThrows(
+            IllegalArgumentException.class,
+            () -> Processing.parseSourceVersion(ImmutableList.of("-source", "NOSUCH")));
+    assertThat(expected).hasMessageThat().contains("invalid -source version: NOSUCH");
+  }
 }