From 4ade45f51f62106375745539152d3acf8f1ab41d Mon Sep 17 00:00:00 2001
From: Irmen de Jong <irmen@razorvine.net>
Date: Sun, 11 Nov 2018 18:19:08 +0100
Subject: [PATCH] tweaking subroutine return values

---
 compiler/examples/test.p8            | 12 ++++++++++++
 compiler/src/prog8/ast/AST.kt        |  3 ++-
 compiler/src/prog8/ast/AstChecker.kt | 17 ++++++++++++-----
 3 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/compiler/examples/test.p8 b/compiler/examples/test.p8
index a414c9b45..50d3007ed 100644
--- a/compiler/examples/test.p8
+++ b/compiler/examples/test.p8
@@ -7,7 +7,19 @@
 
 sub start() {
 
+    ubyte derp
+
+
+    derp=foo()
+    derp=c64.GETADR()
     return
 }
 
+
+sub foo() -> ubyte {
+    return 1            ; @todo not ubyte but byte (if sub returns byte)
+}
+
+
+
 }
diff --git a/compiler/src/prog8/ast/AST.kt b/compiler/src/prog8/ast/AST.kt
index 8c1363d28..badb63f7f 100644
--- a/compiler/src/prog8/ast/AST.kt
+++ b/compiler/src/prog8/ast/AST.kt
@@ -1380,7 +1380,7 @@ class FunctionCall(override var target: IdentifierReference,
                     return null     // no return value
                 if(stmt.returntypes.size==1)
                     return stmt.returntypes[0]
-                return null     // has multiple return types...
+                return null     // has multiple return types... so not a single resulting datatype possible
             }
             is Label -> return null
         }
@@ -1447,6 +1447,7 @@ class AnonymousScope(override var statements: MutableList<IStatement>,
 
 // the subroutine class covers both the normal user-defined subroutines,
 // and also the predefined/ROM/register-based subroutines.
+// (multiple return types can only occur for the latter type)
 class Subroutine(override val name: String,
                  val parameters: List<SubroutineParameter>,
                  val returntypes: List<DataType>,
diff --git a/compiler/src/prog8/ast/AstChecker.kt b/compiler/src/prog8/ast/AstChecker.kt
index 0c81194ad..0b5eb17f2 100644
--- a/compiler/src/prog8/ast/AstChecker.kt
+++ b/compiler/src/prog8/ast/AstChecker.kt
@@ -196,8 +196,9 @@ class AstChecker(private val namespace: INameScope,
         super.process(subroutine)
 
         // user-defined subroutines can only have zero or one return type
+        // (multiple return values are only allowed for asm subs)
         if(!subroutine.isAsmSubroutine && subroutine.returntypes.size>1)
-            err("subroutine has more than one return value")
+            err("subroutines can only have one return value")
 
         // subroutine must contain at least one 'return' or 'goto'
         // (or if it has an asm block, that must contain a 'rts' or 'jmp')
@@ -357,8 +358,15 @@ class AstChecker(private val namespace: INameScope,
             } else {
                 val sourceDatatype: DataType? = assignment.value.resultingDatatype(namespace, heap)
                 if(sourceDatatype==null) {
-                    if(assignment.value is FunctionCall)
-                        checkResult.add(ExpressionError("function call doesn't return a suitable value to use in assignment", assignment.value.position))
+                    if(assignment.value is FunctionCall) {
+                        // a functioncall COULD return multiple values (from an asm subroutine), treat that differently
+                        val stmt = (assignment.value as FunctionCall).target.targetStatement(namespace)
+                        if(stmt is Subroutine && stmt.returntypes.size>1) {
+                            checkResult.add(ExpressionError("subroutine returning multiple values", assignment.value.position))     // TODO check this
+                        }
+                        else
+                            checkResult.add(ExpressionError("function call doesn't return a suitable value to use in assignment", assignment.value.position))
+                    }
                     else
                         checkResult.add(ExpressionError("assignment value is invalid or has no proper datatype", assignment.value.position))
                 }
@@ -633,8 +641,7 @@ class AstChecker(private val namespace: INameScope,
         if(targetStatement!=null)
             checkFunctionCall(targetStatement, functionCall.arglist, functionCall.position)
         if(targetStatement is Subroutine && targetStatement.returntypes.isNotEmpty())
-            if(!targetStatement.isAsmSubroutine)
-                printWarning("result value of subroutine call is discarded", functionCall.position)
+            printWarning("result value of subroutine call is discarded", functionCall.position)
         return super.process(functionCall)
     }