Improve diagnostics for empty and unterminated char literals

MOE_MIGRATED_REVID=216620223

3 files changed, 45 insertions, 7 deletions

diff --git a/java/com/google/turbine/diag/TurbineError.java b/java/com/google/turbine/diag/TurbineError.java
index 01c6c48..f9ddcd5 100644
--- a/java/com/google/turbine/diag/TurbineError.java
+++ b/java/com/google/turbine/diag/TurbineError.java
@@ -34,6 +34,8 @@ public class TurbineError extends Error {
     UNEXPECTED_IDENTIFIER("unexpected identifier '%s'"),
     UNEXPECTED_EOF("unexpected end of input"),
     UNTERMINATED_STRING("unterminated string literal"),
+    UNTERMINATED_CHARACTER_LITERAL("unterminated char literal"),
+    EMPTY_CHARACTER_LITERAL("empty char literal"),
     EXPECTED_TOKEN("expected token %s"),
     INVALID_LITERAL("invalid literal: %s"),
     UNEXPECTED_TYPE_PARAMETER("unexpected type parameter %s"),
diff --git a/java/com/google/turbine/parse/StreamLexer.java b/java/com/google/turbine/parse/StreamLexer.java
index c108332..74b0ce8 100644
--- a/java/com/google/turbine/parse/StreamLexer.java
+++ b/java/com/google/turbine/parse/StreamLexer.java
@@ -339,19 +339,23 @@ public class StreamLexer implements Lexer {
           {
             eat();
             char value;
-            if (ch == '\\') {
-              eat();
-              value = escape();
-            } else {
-              value = ch;
-              eat();
+            switch (ch) {
+              case '\\':
+                eat();
+                value = escape();
+                break;
+              case '\'':
+                throw error(ErrorKind.EMPTY_CHARACTER_LITERAL);
+              default:
+                value = ch;
+                eat();
             }
             if (ch == '\'') {
               saveValue(String.valueOf(value));
               eat();
               return Token.CHAR_LITERAL;
             }
-            throw error(ErrorKind.UNEXPECTED_INPUT, ch);
+            throw error(ErrorKind.UNTERMINATED_CHARACTER_LITERAL);
           }
 
         case '"':
diff --git a/javatests/com/google/turbine/parse/ParseErrorTest.java b/javatests/com/google/turbine/parse/ParseErrorTest.java
index 30ff061..53864ef 100644
--- a/javatests/com/google/turbine/parse/ParseErrorTest.java
+++ b/javatests/com/google/turbine/parse/ParseErrorTest.java
@@ -170,6 +170,38 @@ public class ParseErrorTest {
     }
   }
 
+  @Test
+  public void emptyChar() {
+    String input = "class T { char c = ''; }";
+    try {
+      Parser.parse(input);
+      fail("expected parsing to fail");
+    } catch (TurbineError e) {
+      assertThat(e.getMessage())
+          .isEqualTo(
+              lines(
+                  "<>:1: error: empty char literal", //
+                  "class T { char c = ''; }",
+                  "                    ^"));
+    }
+  }
+
+  @Test
+  public void unterminatedChar() {
+    String input = "class T { char c = '; }";
+    try {
+      Parser.parse(input);
+      fail("expected parsing to fail");
+    } catch (TurbineError e) {
+      assertThat(e.getMessage())
+          .isEqualTo(
+              lines(
+                  "<>:1: error: unterminated char literal", //
+                  "class T { char c = '; }",
+                  "                     ^"));
+    }
+  }
+
   private static String lines(String... lines) {
     return Joiner.on(System.lineSeparator()).join(lines);
   }