[MOREL-205] Pattern that uses nested type-constructors should not be …

…considered redundant

Fixes #205

Adds test cases for #126

src/main/java/net/hydromatic/morel/compile/PatternCoverageChecker.java

@@ -139,7 +139,14 @@ private void toTerm(Core.Pat pat, Path path, List<Sat.Term> terms) {
     case CON_PAT:
       final Core.ConPat conPat = (Core.ConPat) pat;
       terms.add(typeConstructorTerm(path, conPat.tyCon));
-      toTerm(conPat.pat, path, terms);
+      final int j =
+          ImmutableList.copyOf(
+              ((DataType) conPat.type).typeConstructors.keySet())
+              .indexOf(conPat.tyCon);
+      if (j < 0) {
+        throw new AssertionError("type constructor not found: " + conPat);
+      }
+      toTerm(conPat.pat, path.sub(j), terms);
       return;
 
     case CONS_PAT:

src/test/java/net/hydromatic/morel/MainTest.java

@@ -1421,6 +1421,18 @@ public class MainTest {
             });
   }
 
+  /** Test case for "[MOREL-205] Pattern that uses nested type-constructors
+   * should not be considered redundant". */
+  @Test void testMatchCoverage13() {
+    // Even though "SOME i" is seen at depth 1 in the first line,
+    // the "SOME" at depth 0 in the second line is not the same pattern,
+    // therefore the pattern is not redundant.
+    final String ml = "fun f (SOME (SOME i)) = i + 1\n"
+        + "  | f (SOME NONE) = 0\n"
+        + "  | f NONE = ~1\n";
+    ml(ml).assertMatchCoverage(OK);
+  }
+
   /** Function declaration. */
   @Test void testFun() {
     final String ml = "let\n"

src/test/resources/script/datatype.smli

@@ -306,4 +306,37 @@ stdIn:4.1-4.11 Error: operator and operand don't agree [tycon mismatch]
 val it = 3 : int
 *)
 
+(*) Pattern matching on the same type constructor, nested.
+fun f (SOME (SOME i)) = i + 1
+  | f (SOME NONE) = 0
+  | f NONE = ~1;
+> val f = fn : int option option -> int
+f (SOME (SOME 3));
+> val it = 4 : int
+f (SOME (SOME 2));
+> val it = 3 : int
+f (SOME NONE);
+> val it = 0 : int
+f NONE;
+> val it = ~1 : int
+
+(*) Test cases from [MOREL-126].
+fun f ((SOME i) :: NIL) = i + 1
+  | f NIL = 0;
+> val f = fn : int option list -> int
+f [];
+> val it = 0 : int
+f [SOME 5];
+> val it = 6 : int
+
+fun f [(SOME i)] = i
+  | f [] = 0;
+> 0.0-0.0 Warning: match nonexhaustive
+>   raised at: 0.0-0.0
+> val f = fn : int option list -> int
+f [];
+> val it = 0 : int
+f [SOME 5];
+> val it = 5 : int
+
 (*) End datatype.smli