Add a future to lock in the behavior when an iterator is unstable

test/unstable-keyword/iterator/COMPOPTS

@@ -0,0 +1 @@
+--warn-unstable

test/unstable-keyword/iterator/onlySerial.bad

@@ -0,0 +1,35 @@
+onlySerial.chpl:7: In function 'main':
+onlySerial.chpl:9: warning: The serial version of foo is unstable
+onlySerial.chpl:15: warning: The serial version of foo is unstable
+onlySerial.chpl:22: warning: The serial version of foo is unstable
+onlySerial.chpl:68: In iterator 'foo':
+onlySerial.chpl:73: warning: range.translate() is unstable and its behavior may change in the future
+  onlySerial.chpl:22: called as foo(param tag = iterKind.leader)
+onlySerial.chpl:80: In iterator 'foo':
+onlySerial.chpl:85: warning: range.translate() is unstable and its behavior may change in the future
+  $CHPL_HOME/modules/internal/ChapelIteratorSupport.chpl:641: called as foo(param tag = iterKind.follower, followThis: 1*range(int(64),both,one))
+  within internal functions (use --print-callstack-on-error to see)
+onlySerial.chpl:7: In function 'main':
+onlySerial.chpl:31: warning: The serial version of foo is unstable
+testing call of serial
+in the serial iterator
+0
+1
+2
+3
+4
+5
+6
+7
+8
+9
+testing call of standalone
+in the standalone iterator
+0 1 2 3 4 5 6 7 8 9
+testing call of leader (and follower)
+in the leader iterator
+in the follower iterator at least once
+0 2 4 6 8 10 12 14 16 18
+testing call of just follower
+in the follower iterator at least once
+0 3 6 9 12 15 18 21 24 27

test/unstable-keyword/iterator/onlySerial.chpl

@@ -0,0 +1,89 @@
+// Tests behavior when a serial iterator is declared unstable (but none of the
+// others are)
+var rangeToUse = 0..9;
+
+var triggeredFollower: atomic bool = false;
+
+proc main() {
+  writeln("testing call of serial");
+  for i in foo() {
+    writeln(i);
+  }
+
+  writeln("testing call of standalone");
+  var arr1: [rangeToUse] int;
+  forall i in foo() {
+    arr1[i] = i;
+  }
+  writeln(arr1);
+
+  writeln("testing call of leader (and follower)");
+  var arr2: [rangeToUse] int;
+  forall (val, loc) in zip(foo(), arr2) {
+    loc = val*2;
+  }
+  writeln(arr2);
+
+  triggeredFollower.clear();
+
+  writeln("testing call of just follower");
+  var arr3: [rangeToUse] int;
+  forall (loc, val) in zip(arr3, foo()) {
+    loc = val*3;
+  }
+  writeln(arr3);
+}
+
+@unstable("The serial version of foo is unstable")
+iter foo() {
+  writeln("in the serial iterator");
+  for i in rangeToUse {
+    yield i;
+  }
+}
+
+iter foo(param tag) where tag == iterKind.standalone {
+  writeln("in the standalone iterator");
+  for i in rangeToUse {
+    yield i;
+  }
+}
+
+// Stolen from the parallel iterators primer
+proc computeChunk(r: range, myChunk, numChunks) {
+  const numElems = r.size;
+  const elemsperChunk = numElems/numChunks;
+  const rem = numElems%numChunks;
+  var mylow = r.low;
+  if myChunk < rem {
+    mylow += (elemsperChunk+1)*myChunk;
+    return mylow..#(elemsperChunk + 1);
+  } else {
+    mylow += ((elemsperChunk+1)*rem + (elemsperChunk)*(myChunk-rem));
+    return mylow..#elemsperChunk;
+  }
+}
+
+// Partially stolen from the parallel iterators primer
+iter foo(param tag) where tag == iterKind.leader {
+  writeln("in the leader iterator");
+
+  coforall tid in 0..#here.maxTaskPar {
+    const myIters = computeChunk(rangeToUse, tid, here.maxTaskPar);
+    const zeroBasedIters = myIters.translate(-rangeToUse.low);
+
+    yield (zeroBasedIters,);
+  }
+}
+
+// Also stolen from the parallel iterators primer
+iter foo(param tag, followThis) where tag == iterKind.follower {
+  if (triggeredFollower.testAndSet() == false) {
+    writeln("in the follower iterator at least once");
+  }
+  const (followInds,) = followThis;
+  const lowBasedIters = followInds.translate(rangeToUse.low);
+
+  for i in lowBasedIters do
+    yield i;
+}

test/unstable-keyword/iterator/onlySerial.future

@@ -0,0 +1,2 @@
+bug: unstable warnings on iterator overloads trigger too often
+#26590

test/unstable-keyword/iterator/onlySerial.good

@@ -0,0 +1,31 @@
+onlySerial.chpl:7: In function 'main':
+onlySerial.chpl:9: warning: The serial version of foo is unstable
+onlySerial.chpl:68: In iterator 'foo':
+onlySerial.chpl:73: warning: range.translate() is unstable and its behavior may change in the future
+  onlySerial.chpl:22: called as foo(param tag = iterKind.leader)
+onlySerial.chpl:80: In iterator 'foo':
+onlySerial.chpl:85: warning: range.translate() is unstable and its behavior may change in the future
+  $CHPL_HOME/modules/internal/ChapelIteratorSupport.chpl:641: called as foo(param tag = iterKind.follower, followThis: 1*range(int(64),both,one))
+  within internal functions (use --print-callstack-on-error to see)
+testing call of serial
+in the serial iterator
+0
+1
+2
+3
+4
+5
+6
+7
+8
+9
+testing call of standalone
+in the standalone iterator
+0 1 2 3 4 5 6 7 8 9
+testing call of leader (and follower)
+in the leader iterator
+in the follower iterator at least once
+0 2 4 6 8 10 12 14 16 18
+testing call of just follower
+in the follower iterator at least once
+0 3 6 9 12 15 18 21 24 27