From a7a3b1663d709819c535ac8981a4cac6a4a883dd Mon Sep 17 00:00:00 2001
From: FellippeHeitor <fellippeheitor@gmail.com>
Date: Thu, 30 Jun 2016 02:50:10 -0300
Subject: [PATCH] Implements OPTION _EXPLICIT

When you use OPTION _EXPLICIT, all variables and arrays must be defined with DIM (or equivalent statement) before they can be used. QB64's case check already aids in avoiding mistakes on that front, but now you will run into a compiler error if a variable or array is used before being defined.
Because OPTION _EXPLICIT sets a compiler behavior, it must come before any other statements in your code.
As this is a non-QB4.5 feature, the keyword uses an underscore, in order to avoid conflicts with existing code.
---
 source/qb64.bas | 32 ++++++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 8 deletions(-)

diff --git a/source/qb64.bas b/source/qb64.bas
index ac7e0f838..f2ebcabf0 100644
--- a/source/qb64.bas
+++ b/source/qb64.bas
@@ -707,6 +707,7 @@ DIM SHARED cleanupstringprocessingcall AS STRING
 DIM SHARED recompile AS INTEGER 'forces recompilation
 'COMMON SHARED cmemlist() AS INTEGER
 DIM SHARED optionbase AS INTEGER
+DIM SHARED optionexplicit AS _BYTE
 
 DIM SHARED addmetastatic AS INTEGER
 DIM SHARED addmetadynamic AS INTEGER
@@ -1276,6 +1277,7 @@ HashAdd "MOD", f, 0
 f = HASHFLAG_RESERVED + HASHFLAG_CUSTOMSYNTAX
 HashAdd "LIST", f, 0
 HashAdd "BASE", f, 0
+HashAdd "_EXPLICIT", f, 0
 HashAdd "AS", f, 0
 HashAdd "IS", f, 0
 HashAdd "OFF", f, 0
@@ -1426,6 +1428,7 @@ addmetastatic = 0
 addmetadynamic = 0
 DynamicMode = 0
 optionbase = 0
+optionexplicit = 0
 DataOffset = 0
 statementn = 0
 qberrorhappened = 0: qberrorcode = 0: qberrorline = 0
@@ -9581,14 +9584,25 @@ DO
                 END IF
 
                 IF firstelement$ = "OPTION" THEN
-                    IF n <> 3 THEN a$ = "Expected OPTION BASE 0 or 1": GOTO errmes
-                    IF getelement$(a$, 2) <> "BASE" THEN a$ = "Expected OPTION BASE 0 or 1": GOTO errmes
-                    l$ = getelement$(a$, 3)
-                    IF l$ <> "0" AND l$ <> "1" THEN a$ = "Expected OPTION BASE 0 or 1": GOTO errmes
-                    IF l$ = "1" THEN optionbase = 1 ELSE optionbase = 0
-                    l$ = "OPTION" + sp + "BASE" + sp + l$
-                    layoutdone = 1: IF LEN(layout$) THEN layout$ = layout$ + sp + l$ ELSE layout$ = l$
-                    GOTO finishedline
+                    IF n = 1 THEN a$ = "Expected OPTION BASE or OPTION _EXPLICIT": GOTO errmes
+                    e$ = getelement$(a$, 2)
+                    SELECT CASE e$
+                        CASE "BASE"
+                            l$ = getelement$(a$, 3)
+                            IF l$ <> "0" AND l$ <> "1" THEN a$ = "Expected OPTION BASE 0 or 1": GOTO errmes
+                            IF l$ = "1" THEN optionbase = 1 ELSE optionbase = 0
+                            l$ = "OPTION" + sp + "BASE" + sp + l$
+                            layoutdone = 1: IF LEN(layout$) THEN layout$ = layout$ + sp + l$ ELSE layout$ = l$
+                            GOTO finishedline
+                        CASE "_EXPLICIT"
+                            IF linenumber > 1 THEN a$ = "OPTION _EXPLICIT must come before any other statement": GOTO errmes
+                            optionexplicit = -1
+                            l$ = "OPTION" + sp + "_EXPLICIT"
+                            layoutdone = 1: IF LEN(layout$) THEN layout$ = layout$ + sp + l$ ELSE layout$ = l$
+                            GOTO finishedline
+                        CASE ELSE
+                            a$ = "Expected OPTION BASE or OPTION _EXPLICIT": GOTO errmes
+                    END SELECT
                 END IF
 
                 'any other "unique" subs can be processed above
@@ -14573,6 +14587,7 @@ FUNCTION evaluate$ (a2$, typ AS LONG)
                             NEXT
                             fakee$ = "10": FOR i2 = 2 TO nume: fakee$ = fakee$ + sp + "," + sp + "10": NEXT
                             IF Debug THEN PRINT #9, "evaluate:creating undefined array using dim2(" + l$ + "," + dtyp$ + ",1," + fakee$ + ")"
+                            IF optionexplicit THEN Give_Error "Array not defined": EXIT FUNCTION
                             IF Error_Happened THEN EXIT FUNCTION
                             olddimstatic = dimstatic
                             method = 1
@@ -14793,6 +14808,7 @@ FUNCTION evaluate$ (a2$, typ AS LONG)
                     LOOP
 
                     IF Debug THEN PRINT #9, "CREATING VARIABLE:" + x$
+                    IF optionexplicit THEN Give_Error "Variable not defined": EXIT FUNCTION
                     retval = dim2(x$, typ$, 1, "")
                     IF Error_Happened THEN EXIT FUNCTION