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Preserve empty variant constructor in data-deps. #7303

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Sep 2, 2020
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Preserve empty variant constructor in data-deps. #7303

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31a694c
Preserve empty variant constructor in data-deps.
sofiafaro-da Sep 2, 2020
1cca2ae
Add special case for single constructor variants
sofiafaro-da Sep 2, 2020
59926ba
Add test for special case
sofiafaro-da Sep 2, 2020
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Preserve empty variant constructor in data-deps. 
This fixes #7207 and adds a regression test. In a
separate PR I'll add a warning for variants with
single argument of unit type and add a changelog
entry.

changelog_begin
changelog_end
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@sofiafaro-da
sofiafaro-da committed Sep 2, 2020
commit 31a694c978115df5d7f60920803625162cbf67f4
3 changes: 3 additions & 0 deletions compiler/damlc/daml-compiler/src/DA/Daml/Compiler/DataDependencies.hs
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Expand Up @@ -479,6 +479,9 @@ generateSrcFromLf env = noLoc mod

convConDetails :: LF.Type -> Gen (HsConDeclDetails GhcPs)
convConDetails = \case
-- empty variant constructor (see issue #7207)
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"Empty" is such an overloaded word:

Suggested change
-- empty variant constructor (see issue #7207)
-- variant constructor without argument (see issue #7207)

Or "payload" instead of "argument".

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Right, but "variant constructor without argument" is such a clumsy phrase, and what else could "empty variant constructor" mean?

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I guess the right answer here is "nullary variant constructor".

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I like "nullary variant constructor". 👍

LF.TUnit ->
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This means that a variant where I explicilty specify a Unit argument will also be decompiled to a Prefix con right? I think that’s perfectly reasonable but probably worth documenting in a comment and perhaps warning on in the preprocessor.

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Yes, that's what we decided on in the issue and I'm preparing the warning in a separate PR.

pure $ PrefixCon []

-- variant record constructor
LF.TConApp LF.Qualified{..} _
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43 changes: 43 additions & 0 deletions compiler/damlc/tests/src/DA/Test/Packaging.hs
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Expand Up @@ -1667,6 +1667,49 @@ dataDependencyTests Tools{damlc,repl,validate,davlDar,oldProjDar} = testGroup "D
withCurrentDirectory (tmpDir </> "proj") $
callProcessSilent damlc ["build"]

, testCaseSteps "Empty variant constructors" $ \step -> withTempDir $ \tmpDir -> do
-- This test checks that variant constructors without argument
-- are preserved. This is a regression test for issue #7207.
step "building project with type definition"
createDirectoryIfMissing True (tmpDir </> "type")
writeFileUTF8 (tmpDir </> "type" </> "daml.yaml") $ unlines
[ "sdk-version: " <> sdkVersion
, "name: type"
, "source: ."
, "version: 0.1.0"
, "dependencies: [daml-prim, daml-stdlib]"
]
writeFileUTF8 (tmpDir </> "type" </> "Foo.daml") $ unlines
[ "module Foo where"
, "data A = B | C Int"
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Should we add a third case D () and check that it behaves like D when imported as data-dependency?

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I don't think so. D () is something we're deprecating, and the fact that it's treated the same as D in the current compiler is mostly a mistake.

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I generally agree but would feel more comfortable to have a test as long as users can still write it, even though they get warned about it.

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@sofiafaro-da sofiafaro-da Sep 2, 2020 •
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I added a test for D () in the single constructor case, which is something we had talked about adding as a special case (since we can't distinguish single-constructor variants from enums any other way, and there's no ambiguity in the single constructor case). (This actually also came up in one of the other tests, but better to add one here as well.)

]
withCurrentDirectory (tmpDir </> "type") $
callProcessSilent damlc ["build", "-o", "type.dar"]

step "building project that uses it via data-dependencies"
createDirectoryIfMissing True (tmpDir </> "proj")
writeFileUTF8 (tmpDir </> "proj" </> "daml.yaml") $ unlines
[ "sdk-version: " <> sdkVersion
, "name: proj"
, "source: ."
, "version: 0.1.0"
, "dependencies: [daml-prim, daml-stdlib]"
, "data-dependencies: "
, " - " <> (tmpDir </> "type" </> "type.dar")
]
writeFileUTF8 (tmpDir </> "proj" </> "Main.daml") $ unlines
[ "module Main where"
, "import Foo"
, "mkA : A"
, "mkA = B"
, "matchA : A -> Int"
, "matchA a ="
, " case a of"
, " B -> 0"
, " C n -> n"
]
withCurrentDirectory (tmpDir </> "proj") $
callProcessSilent damlc ["build"]
]

-- | Check that the given file exists in the dar in the given directory.
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