fix crash on empty conditional branch statement (if_cc { } )

codeGenCpu6502/src/prog8/codegen/cpu6502/AsmGen.kt

@@ -794,7 +794,7 @@ $repeatLabel    lda  $counterVar
         if(stmt.truepart.isEmpty() && stmt.elsepart.isNotEmpty())
             throw AssemblyError("only else part contains code, shoud have been switched already")
 
-        val jump = stmt.truepart.statements.first() as? Jump
+        val jump = stmt.truepart.statements.firstOrNull() as? Jump
         if(jump!=null) {
             // branch with only a jump (goto)
             val instruction = branchInstruction(stmt.condition, false)
@@ -812,11 +812,13 @@ $repeatLabel    lda  $counterVar
             translate(stmt.elsepart)
         } else {
             if(stmt.elsepart.isEmpty()) {
-                val instruction = branchInstruction(stmt.condition, true)
-                val elseLabel = program.makeLabel("branch_else")
-                out("  $instruction  $elseLabel")
-                translate(stmt.truepart)
-                out(elseLabel)
+                if(stmt.truepart.isNotEmpty()) {
+                    val instruction = branchInstruction(stmt.condition, true)
+                    val elseLabel = program.makeLabel("branch_else")
+                    out("  $instruction  $elseLabel")
+                    translate(stmt.truepart)
+                    out(elseLabel)
+                }
             } else {
                 val instruction = branchInstruction(stmt.condition, true)
                 val elseLabel = program.makeLabel("branch_else")

compiler/src/prog8/compiler/astprocessing/VariousCleanups.kt

@@ -8,6 +8,8 @@ import prog8.ast.base.FatalAstException
 import prog8.ast.expressions.*
 import prog8.ast.statements.AnonymousScope
 import prog8.ast.statements.Assignment
+import prog8.ast.statements.ConditionalBranch
+import prog8.ast.statements.IfElse
 import prog8.ast.walk.AstWalker
 import prog8.ast.walk.IAstModification
 import prog8.code.core.*
@@ -219,5 +221,22 @@ internal class VariousCleanups(val program: Program, val errors: IErrorReporter,
         }
         return noModifications
     }
+
+    override fun after(branch: ConditionalBranch, parent: Node): Iterable<IAstModification> {
+        if(branch.truepart.isEmpty() && branch.elsepart.isEmpty()) {
+            errors.warn("removing empty conditional branch", branch.position)
+            return listOf(IAstModification.Remove(branch, parent as IStatementContainer))
+        }
+
+        return noModifications
+    }
+
+    override fun after(ifElse: IfElse, parent: Node): Iterable<IAstModification> {
+        if(ifElse.truepart.isEmpty() && ifElse.elsepart.isEmpty()) {
+            errors.warn("removing empty if-else statement", ifElse.position)
+            return listOf(IAstModification.Remove(ifElse, parent as IStatementContainer))
+        }
+        return noModifications
+    }
 }
 

compiler/test/ast/TestProg8Parser.kt

@@ -888,9 +888,11 @@ class TestProg8Parser: FunSpec( {
                     bool bb
                     ubyte cc
                     if cc in [' ', '@', 0] {
+                        cx16.r0L++
                     }
                     
                     if cc in "email" {
+                        cx16.r0L++
                     }
                     
                     bb = 99 in array

docs/source/todo.rst

@@ -4,6 +4,7 @@ TODO
 For next release
 ^^^^^^^^^^^^^^^^
 - get rid of diskio.have_first_byte.  But detecting invalid filenames should still work.
+- check diskio.status(), fix diskio.f_readline
 - diskio.f_read doesn't signal end of file condition if the requested number of bytes==1 ?
 - diskio.f_read doesn't work if used after seek with buffer too small?
 - ir/vm: check weird asm chunks appearing in block?