Java: Improve documentation regarding minus in front of numeric literals

Author: Marcono1234

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

@@ -638,25 +638,62 @@ class BooleanLiteral extends Literal, @booleanliteral {
   override string getAPrimaryQlClass() { result = "BooleanLiteral" }
 }
 
-/** An integer literal. For example, `23`. */
+/**
+ * An integer literal. For example, `23`.
+ *
+ * An integer literal can never be negative except when:
+ * - It is written in binary, octal or hexadecimal notation
+ * - It is written in decimal notation, has the value `2147483648` and is preceded
+ *   by a minus; in this case the value of the IntegerLiteral is -2147483648 and
+ *   the preceding minus will *not* be modeled as `MinusExpr`.<br/>
+ *   In all other cases the preceding minus, if any, will be modeled as separate
+ *   `MinusExpr`.
+ *
+ * The last exception is necessary because `2147483648` on its own would not be
+ * a valid integer literal (and could also not be parsed as CodeQL `int`).
+ */
 class IntegerLiteral extends Literal, @integerliteral {
   /** Gets the int representation of this literal. */
   int getIntValue() { result = getValue().toInt() }
 
   override string getAPrimaryQlClass() { result = "IntegerLiteral" }
 }
 
-/** A long literal. For example, `23l`. */
+/**
+ * A long literal. For example, `23L`.
+ *
+ * A long literal can never be negative except when:
+ * - It is written in binary, octal or hexadecimal notation
+ * - It is written in decimal notation, has the value `9223372036854775808` and
+ *   is preceded by a minus; in this case the value of the LongLiteral is
+ *   -9223372036854775808 and the preceding minus will *not* be modeled as
+ *   `MinusExpr`.<br/>
+ *   In all other cases the preceding minus, if any, will be modeled as separate
+ *   `MinusExpr`.
+ *
+ * The last exception is necessary because `9223372036854775808` on its own
+ * would not be a valid long literal.
+ */
 class LongLiteral extends Literal, @longliteral {
   override string getAPrimaryQlClass() { result = "LongLiteral" }
 }
 
-/** A floating point literal. For example, `4.2f`. */
+/**
+ * A float literal. For example, `4.2f`.
+ *
+ * A float literal is never negative; a preceding minus, if any, will always
+ * be modeled as separate `MinusExpr`.
+ */
 class FloatingPointLiteral extends Literal, @floatingpointliteral {
   override string getAPrimaryQlClass() { result = "FloatingPointLiteral" }
 }
 
-/** A double literal. For example, `4.2`. */
+/**
+ * A double literal. For example, `4.2`.
+ *
+ * A double literal is never negative; a preceding minus, if any, will always
+ * be modeled as separate `MinusExpr`.
+ */
 class DoubleLiteral extends Literal, @doubleliteral {
   override string getAPrimaryQlClass() { result = "DoubleLiteral" }
 }