Add some tests for E2

Currently the tests are quite minimal: a test for the E2 parser, and a
regression test for #1975. Soon there will be a test harness command
that runs all the test E2s and watches for errors.

data/expression2/tests/parsing.txt

@@ -0,0 +1,88 @@
+@inputs In
+@outputs Out
+
+local A = 0
+
+if (A) { A = 0 }
+if (A) { A = 0 } else { A = 0 }
+if (A) { A = 0 } elseif (A) { A = 0 }
+if (A) { A = 0 } elseif (A) { A = 0 }
+
+while (A) { A = 0 }
+
+for (B = 1, 2) { A = 0 }
+for (B = 1, 2, 3) { A = 0 }
+
+foreach (K, V: number = array(1, 2, 3)) { A = 0 }
+
+while (A) { break }
+while (A) { continue }
+
+A++
+A--
+A += 1
+A -= 1
+A *= 1
+A /= 1
+
+local B = vec()
+B[1] = 2
+
+switch (A) {
+    case A + A,
+        A = 0
+        A = 0
+    case A + A + A,
+        A = 0
+        break
+    default,
+        A = 0
+}
+
+function f() {}
+function void f() {}
+function void f() { return }
+function number g() { return 0 }
+function number f(X) { return X }
+function vector f(X: vector) { return X }
+function number f(X, Y) { return X + Y }
+function number f(X, Y: vector) { return X }
+function number f([X Y]) { return X + Y }
+function number f([X Y]: number) { return X + Y }
+
+A ? A : A
+A ?: A
+A | A
+A & A
+A || A
+A && A
+A ^^ A
+A == A
+A != A
+A > A
+A < A
+A >= A
+A <= A
+A << A
+A >> A
+A + A
+A - A
+A * A
+A / A
+A % A
+A ^ A
++A
+-A
+!A
+
+array():count()
+array()[0, number]
+(A)
+0
+"foo"
+~In
+$In
+->In
+A
+
+table(1 = 1, 2 = 2)

data/expression2/tests/regressions/1975.txt

@@ -0,0 +1,11 @@
+vec() * 0
+0 * vec()
+
+local Calls = 0
+function number f() {
+    Calls++
+    return 1
+}
+f() * 0
+0 * f()
+assert(Calls == 2)

lua/entities/gmod_wire_expression2/core/core.lua

@@ -318,6 +318,14 @@ e2function void error( string reason )
 	error(reason, 2)
 end
 
+e2function void assert(condition)
+	if not condition then error("assert failed", 2) end
+end
+
+e2function void assert(condition, string reason)
+	if not condition then error(reason, 2) end
+end
+
 --------------------------------------------------------------------------------
 
 __e2setcost(100) -- approximation

lua/wire/client/e2descriptions.lua

@@ -824,6 +824,8 @@ E2Helper.Descriptions["setName(e:s)"] = "Set the name of another E2 or component
 E2Helper.Descriptions["cpuUsage()"] = "Returns the average time per tick the server spends running this E2, in seconds (multiply it by 1000000 to get the same value as is displayed on the E2 overlay)"
 E2Helper.Descriptions["cpuUsage(e:)"] = "Returns the average time per tick the server spends running the specified E2, in seconds (multiply it by 1000000 to get the same value as is displayed on the E2 overlay)"
 E2Helper.Descriptions["error(s)"] = "Shuts down the E2 with specified script error message"
+E2Helper.Descriptions["assert(n)"] = "If the argument is 0, shut down the E2 with an error message"
+E2Helper.Descriptions["assert(ns)"] = "If the first argument is 0, shut down the E2 with the given error message string"
 E2Helper.Descriptions["reset()"] = "Reset the expression itself as if it was just spawned, stops execution"
 E2Helper.Descriptions["exit()"] = "Stops the execution of any code after it"
 E2Helper.Descriptions["getCode()"] = "Returns the code of the E2 as a string"