Revert 8325, Add CharacterLiteral to CompileTimeConstantExpr.getStringValue

As pointed out in 8325's thread, this breaks the corner case of char-literal addition and the convention that getStringValue only applies to String-typed constants.

Author: smowton

java/ql/lib/semmle/code/java/Expr.qll

@@ -168,8 +168,6 @@ class CompileTimeConstantExpr extends Expr {
   string getStringValue() {
     result = this.(StringLiteral).getValue()
     or
-    result = this.(CharacterLiteral).getValue()
-    or
     result =
       this.(AddExpr).getLeftOperand().(CompileTimeConstantExpr).getStringValue() +
         this.(AddExpr).getRightOperand().(CompileTimeConstantExpr).getStringValue()

java/ql/test/library-tests/constants/CompileTimeConstantExpr.expected

@@ -15,4 +15,3 @@
 | constants/Constants.java:20:22:20:22 | 5 |
 | constants/Constants.java:20:27:20:27 | 1 |
 | constants/Constants.java:20:31:20:31 | 2 |
-| constants/Constants.java:21:22:21:24 | 'a' |

java/ql/test/library-tests/constants/PrintAst.expected

@@ -66,11 +66,7 @@ constants/Constants.java:
 #   20|                 1: [IntegerLiteral] 5
 #   20|               1: [IntegerLiteral] 1
 #   20|               2: [IntegerLiteral] 2
-#   21|         11: [LocalVariableDeclStmt] var ...;
-#   21|           0: [TypeAccess] char
-#   21|           1: [LocalVariableDeclExpr] charLiteral
-#   21|             0: [CharacterLiteral] 'a'
-#   23|         12: [ReturnStmt] return ...
+#   22|         11: [ReturnStmt] return ...
 constants/Initializers.java:
 #    0| [CompilationUnit] Initializers
 #    3|   1: [Class] Initializers
@@ -516,13 +512,3 @@ constants/Values.java:
 #   90|           0: [TypeAccess] int
 #   90|           1: [LocalVariableDeclExpr] var_nonfinald_local
 #   90|             0: [VarAccess] var_field
-#   91|         68: [LocalVariableDeclStmt] var ...;
-#   91|           0: [TypeAccess] String
-#   91|           1: [LocalVariableDeclExpr] concatenatedString
-#   91|             0: [StringLiteral] "a" + "b"
-#   92|         69: [LocalVariableDeclStmt] var ...;
-#   92|           0: [TypeAccess] String
-#   92|           1: [LocalVariableDeclExpr] concatenatedChar
-#   92|             0: [AddExpr] ... + ...
-#   92|               0: [StringLiteral] "ab"
-#   92|               1: [CharacterLiteral] 'c'

java/ql/test/library-tests/constants/constants/Constants.java

@@ -18,7 +18,6 @@ void constants(final int notConstant) {
 		int paren = (12);
 		String string = "a string";
 		int ternary = (3 < 5) ? 1 : 2;
-		char charLiteral = 'a';
 
 		return;
 	}

java/ql/test/library-tests/constants/constants/Values.java

@@ -88,7 +88,5 @@ void values(final int notConstant) {
         int var_local = final_local; //42
         int var_param = notConstant; //Not constant
         int var_nonfinald_local = var_field; //Not constant
-        String concatenatedString = "a" + "b"; //ab
-        String concatenatedChar = "ab" + 'c'; //abc
     }
 }