Use Java 8 bytecode at minimum

Follow-up to https://github.com/google/turbine/commit/006a74b6cd7565221a2d7fe9593c103bdd83584c. Supporting `-source 7 -target 7` regresses
support for type annotations, since turbine continues to emit the
attributes but they aren't recognized in v51 class files.

PiperOrigin-RevId: 399244322

2 files changed, 37 insertions, 1 deletions

diff --git a/java/com/google/turbine/lower/Lower.java b/java/com/google/turbine/lower/Lower.java
index 39df9d1..9b2d49f 100644
--- a/java/com/google/turbine/lower/Lower.java
+++ b/java/com/google/turbine/lower/Lower.java
@@ -18,6 +18,7 @@ package com.google.turbine.lower;
 
 import static com.google.common.collect.Iterables.getOnlyElement;
 import static com.google.turbine.binder.DisambiguateTypeAnnotations.groupRepeated;
+import static java.lang.Math.max;
 import static java.util.Objects.requireNonNull;
 
 import com.google.common.base.Function;
@@ -121,7 +122,8 @@ public class Lower {
         CompoundEnv.<ClassSymbol, TypeBoundClass>of(classpath).append(new SimpleEnv<>(units));
     ImmutableMap.Builder<String, byte[]> result = ImmutableMap.builder();
     Set<ClassSymbol> symbols = new LinkedHashSet<>();
-    int majorVersion = languageVersion.majorVersion();
+    // Output Java 8 bytecode at minimum, for type annotations
+    int majorVersion = max(languageVersion.majorVersion(), 52);
     for (ClassSymbol sym : units.keySet()) {
       result.put(sym.binaryName(), lower(units.get(sym), env, sym, symbols, majorVersion));
     }
diff --git a/javatests/com/google/turbine/lower/LowerTest.java b/javatests/com/google/turbine/lower/LowerTest.java
index d95cd57..67fb549 100644
--- a/javatests/com/google/turbine/lower/LowerTest.java
+++ b/javatests/com/google/turbine/lower/LowerTest.java
@@ -638,6 +638,40 @@ public class LowerTest {
     assertThat((testAccess[0] & TurbineFlag.ACC_PROTECTED)).isNotEqualTo(TurbineFlag.ACC_PROTECTED);
   }
 
+  @Test
+  public void minClassVersion() throws Exception {
+    BindingResult bound =
+        Binder.bind(
+            ImmutableList.of(Parser.parse("class Test {}")),
+            ClassPathBinder.bindClasspath(ImmutableList.of()),
+            TURBINE_BOOTCLASSPATH,
+            /* moduleVersion=*/ Optional.empty());
+    Map<String, byte[]> lowered =
+        Lower.lowerAll(
+                LanguageVersion.fromJavacopts(ImmutableList.of("-source", "7", "-target", "7")),
+                bound.units(),
+                bound.modules(),
+                bound.classPathEnv())
+            .bytes();
+    int[] major = {0};
+    new ClassReader(lowered.get("Test"))
+        .accept(
+            new ClassVisitor(Opcodes.ASM9) {
+              @Override
+              public void visit(
+                  int version,
+                  int access,
+                  String name,
+                  String signature,
+                  String superName,
+                  String[] interfaces) {
+                major[0] = version;
+              }
+            },
+            0);
+    assertThat(major[0]).isEqualTo(Opcodes.V1_8);
+  }
+
   static String lines(String... lines) {
     return Joiner.on(System.lineSeparator()).join(lines);
   }