stricter set type match, implicit conversion for literals (#24176) devel

fixes #18396, fixes #20142

Set types with base types matching less than a generic match (so
subrange matches, conversion matches, int conversion matches) are now
considered mismatching, as their representation is different on the
backends (except VM and JS), causing codegen issues. An exception is
granted for set literal types, which now implicitly convert each element
to the matched base type, so things like `s == {'a', 'b'}` are still
possible where `s` is `set[range['a'..'z']]`. Also every conversion
match in this case is unified under the normal "conversion" match, so a
literal doesn't match one set type better than the other, unless it's
equal.

However `{'a', 'b'} == s` or `{'a', 'b'} - s` etc is now not possible.
when it used to work in the VM. So this is somewhat breaking, and needs
a changelog entry.

2 files changed, 34 insertions, 3 deletions

diff --git a/tests/sets/trangeincompatible.nim b/tests/sets/trangeincompatible.nim
new file mode 100644
index 000000000..554a50235
--- /dev/null
+++ b/tests/sets/trangeincompatible.nim
@@ -0,0 +1,32 @@
+block: # issue #20142
+  let
+    s1: set['a' .. 'g'] = {'a', 'e'}
+    s2: set['a' .. 'g'] = {'b', 'c', 'd', 'f'} # this works fine
+    s3 = {'b', 'c', 'd', 'f'}
+
+  doAssert s1 != s2
+  doAssert s1 == {range['a'..'g'] 'a', 'e'}
+  doAssert s2 == {range['a'..'g'] 'b', 'c', 'd', 'f'}
+  # literal conversion:
+  doAssert s1 == {'a', 'e'}
+  doAssert s2 == {'b', 'c', 'd', 'f'}
+  doAssert s3 == {'b', 'c', 'd', 'f'}
+  doAssert not compiles(s1 == s3)
+  doAssert not compiles(s2 == s3)
+  # can't convert literal 'z', overload match fails
+  doAssert not compiles(s1 == {'a', 'z'})
+
+block: # issue #18396
+  var s1: set[char] = {'a', 'b'}
+  var s2: set['a'..'z'] = {'a', 'b'}
+  doAssert s1 == {'a', 'b'}
+  doAssert s2 == {range['a'..'z'] 'a', 'b'}
+  doAssert s2 == {'a', 'b'}
+  doAssert not compiles(s1 == s2)
+
+block: # issue #16270
+  var s1: set[char] = {'a', 'b'}
+  var s2: set['a'..'z'] = {'a', 'c'}
+  doAssert not (compiles do: s2 = s2 + s1)
+  s2 = s2 + {'a', 'b'}
+  doAssert s2 == {'a', 'b', 'c'}
diff --git a/tests/sets/twrongenumrange.nim b/tests/sets/twrongenumrange.nim
index fc90c142f..a8d64ac44 100644
--- a/tests/sets/twrongenumrange.nim
+++ b/tests/sets/twrongenumrange.nim
@@ -45,7 +45,6 @@ block:
     TNoteKind = range[k1..k2]
   var notes: set[TNoteKind]
   notes = {k0} #[tt.Error
-           ^ cannot convert 'k0' to 'TNoteKind = range 1..2(TMsgKind)]#
+          ^ type mismatch: got <set[TMsgKind]> but expected 'set[TNoteKind]']#
   notes = {k0..k3} #[tt.Error
-           ^ cannot convert 'k0' to 'TNoteKind = range 1..2(TMsgKind)'; tt.Error
-               ^ cannot convert 'k3' to 'TNoteKind = range 1..2(TMsgKind)']#
+          ^ type mismatch: got <set[TMsgKind]> but expected 'set[TNoteKind]']#