stricter type checking in multivalue assigns, avoids possible invalid output due to missing type cast

compiler/src/prog8/compiler/astprocessing/AstChecker.kt

@@ -642,7 +642,7 @@ internal class AstChecker(private val program: Program,
         fcallTarget.returntypes.zip(targets).withIndex().forEach { (index, p) ->
             val (returnType, target) = p
             val targetDt = target.inferType(program).getOrUndef()
-            if (!target.void && !(returnType isAssignableTo targetDt))
+            if (!target.void && returnType != targetDt)
                 errors.err("can't assign returnvalue #${index + 1} to corresponding target; $returnType vs $targetDt", target.position)
         }
     }

compiler/test/ast/TestAstChecks.kt

@@ -417,4 +417,31 @@ main {
         errors.errors[1] shouldContain  ":6:16: argument 1 type mismatch"
         errors.errors[2] shouldContain  ":12:16: this pass-by-reference type can't be used as a parameter type"
     }
+
+    test("proper type checking for multi-value assigns") {
+        val src="""
+main {
+    sub start() {
+        bool bb
+        ubyte ub
+        uword uw
+        uw, void = thing2()
+        uw, bb = thing2()
+        uw, ub = thing2()
+    }
+
+    asmsub thing2() -> ubyte @A, bool @Pc {
+        %asm {{
+            rts
+        }}
+    }
+}"""
+        val errors = ErrorReporterForTests()
+        compileText(C64Target(), false, src, writeAssembly = false, errors = errors) shouldBe null
+        errors.errors.size shouldBe 4
+        errors.errors[0] shouldContain  "can't assign returnvalue #1 to corresponding target; ubyte vs uword"
+        errors.errors[1] shouldContain  "can't assign returnvalue #1 to corresponding target; ubyte vs uword"
+        errors.errors[2] shouldContain  "can't assign returnvalue #1 to corresponding target; ubyte vs uword"
+        errors.errors[3] shouldContain  "can't assign returnvalue #2 to corresponding target; bool vs ubyte"
+    }
 })

examples/test.p8

@@ -1,11 +1,22 @@
 %import textio
-
 %zeropage basicsafe
-
+%option no_sysinit
 
 main {
     sub start() {
-        txt.plot(20,5)
-        txt.print("hello")
+        bool bb
+        ubyte ub
+        uword uw
+        uw, void = thing2()
+        uw, bb = thing2()
+        uw, ub = thing2()
+    }
+
+    asmsub thing2() -> ubyte @A, bool @Pc {
+        %asm {{
+            lda #$aa
+            clc
+            rts
+        }}
     }
 }