Add GHC-18157

Author: ryndubei

message-index/messages/GHC-18157/index.md

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+---
+title: GHC stage restriction
+summary: A local name is used in a top-level splice, quasi-quote or annotation.
+severity: error
+introduced: 9.8.1
+---
+
+A top-level
+[Template Haskell splice](https://downloads.haskell.org/ghc/latest/docs/html/users_guide/exts/template_haskell.html#syntax),
+[quasi-quote](https://downloads.haskell.org/ghc/latest/docs/users_guide/exts/template_haskell.html#template-haskell-quasi-quotation)
+or
+[source annotation](https://downloads.haskell.org/ghc/latest/docs/users_guide/extending_ghc.html#source-annotations).
+cannot directly call a variable bound in the same module.

message-index/messages/GHC-18157/stage-restriction-anns/after/Bar.hs

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+module Bar (bar) where
+
+bar :: Integer
+bar = 2

message-index/messages/GHC-18157/stage-restriction-anns/after/Example.hs

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+module Example where
+
+import Bar (bar)
+
+{-# ANN foo bar #-}
+foo :: Integer
+foo = 1

message-index/messages/GHC-18157/stage-restriction-anns/before/Example.hs

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+module Example where
+
+{-# ANN foo bar #-}
+foo :: Integer
+foo = 1
+
+bar :: Integer
+bar = 2

message-index/messages/GHC-18157/stage-restriction-anns/index.md

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+---
+title: A local name is used in an annotation.
+---
+
+`foo` and `bar` are both defined in the same module, causing the error.
+
+# Error Message
+```
+Example.hs:3:13: error: [GHC-18157]
+    • GHC stage restriction:
+        ‘bar’ is used in a top-level splice, quasi-quote, or annotation,
+        and must be imported, not defined locally
+    • In the annotation: {-# ANN foo bar #-}
+  |
+3 | {-# ANN foo bar #-}
+  |             ^^^
+```

message-index/messages/GHC-18157/stage-restriction-qq/after/Example.hs

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+{-# LANGUAGE QuasiQuotes #-}
+module Example where
+
+import QQ (qq)
+
+foo :: String
+foo = [qq|1|]

message-index/messages/GHC-18157/stage-restriction-qq/after/QQ.hs

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+module QQ (qq) where
+
+import Language.Haskell.TH.Quote
+import Language.Haskell.TH
+
+qq :: QuasiQuoter
+qq = QuasiQuoter
+  { quoteExp = pure . LitE . StringL
+  , quoteDec = undefined
+  , quotePat = undefined
+  , quoteType = undefined
+  }

message-index/messages/GHC-18157/stage-restriction-qq/before/Example.hs

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+{-# LANGUAGE QuasiQuotes #-}
+module Example where
+
+import Language.Haskell.TH.Quote
+import Language.Haskell.TH
+
+qq :: QuasiQuoter
+qq = QuasiQuoter
+  { quoteExp = pure . LitE . StringL
+  , quoteDec = undefined
+  , quotePat = undefined
+  , quoteType = undefined
+  }
+
+foo :: String
+foo = [qq|bar|]

message-index/messages/GHC-18157/stage-restriction-qq/index.md

@@ -0,0 +1,17 @@
+---
+title: A local name is used in a quasi-quote.
+---
+
+`foo` and `qq` are both defined in the same module, causing the error.
+
+# Error Message
+```
+Example.hs:16:7: error: [GHC-18157]
+    • GHC stage restriction:
+        ‘qq’ is used in a top-level splice, quasi-quote, or annotation,
+        and must be imported, not defined locally
+    • In the quasi-quotation: [qq|bar|]
+   |
+16 | foo = [qq|bar|]
+   |       ^^^^^^^^^
+```

message-index/messages/GHC-18157/stage-restriction-splice-1/after/Example.hs

@@ -0,0 +1,8 @@
+{-# LANGUAGE TemplateHaskell #-}
+module Example where
+
+import Foo (foo)
+import Language.Haskell.TH
+
+x :: Integer
+x = $foo

message-index/messages/GHC-18157/stage-restriction-splice-1/after/Foo.hs

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+module Foo (foo) where
+
+import Language.Haskell.TH
+
+foo :: Q Exp
+foo = pure . LitE $ IntegerL 1

message-index/messages/GHC-18157/stage-restriction-splice-1/before/Example.hs

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+{-# LANGUAGE TemplateHaskell #-}
+module Example where
+
+import Language.Haskell.TH
+
+foo :: Q Exp
+foo = pure . LitE $ IntegerL 1
+
+x :: Integer
+x = $foo

message-index/messages/GHC-18157/stage-restriction-splice-1/index.md

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+---
+title: A local name is used in a top-level splice.
+---
+
+`x` and `foo` are both defined in the same module, causing the error.
+
+# Error Message
+```
+Example.hs:10:6: error: [GHC-18157]
+    • GHC stage restriction:
+        ‘foo’ is used in a top-level splice, quasi-quote, or annotation,
+        and must be imported, not defined locally
+    • In the untyped splice: $foo
+   |
+10 | x = $foo
+   |      ^^^
+```

message-index/messages/GHC-18157/stage-restriction-splice-2/after/Example.hs

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+{-# LANGUAGE TemplateHaskell #-}
+module Example where
+
+import TH (doSomethingWithName)
+
+foo :: Int
+foo = 1
+
+doSomethingWithName 'foo

message-index/messages/GHC-18157/stage-restriction-splice-2/after/TH.hs

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+module TH (doSomethingWithName) where
+
+import Language.Haskell.TH
+
+doSomethingWithName :: Name -> DecsQ
+doSomethingWithName x = pure []

message-index/messages/GHC-18157/stage-restriction-splice-2/before/Example.hs

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+{-# LANGUAGE TemplateHaskell #-}
+module Example where
+
+import TH (doSomethingWith)
+
+foo :: Int
+foo = 1
+
+doSomethingWith foo

message-index/messages/GHC-18157/stage-restriction-splice-2/before/TH.hs

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+module TH (doSomethingWith) where
+
+import Language.Haskell.TH
+
+doSomethingWith :: Int -> DecsQ
+doSomethingWith x = pure []

message-index/messages/GHC-18157/stage-restriction-splice-2/index.md

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+---
+title: A local name is used in a top-level splice as a function argument.
+---
+
+The error message given by GHC is slightly misleading: you cannot pass a
+_variable_ bound in the same module to a top-level splice, but you can pass in
+just the `Name`. The name must be bound above the splice in the module file.
+
+Depending on the information you need from the variable, this can be an
+alternative to moving the variable binding to a different module.
+
+The syntax for the `Name` literal of a function `f` is `'f`, and the `Name` of a
+type `T` is `''T`. To extract information from a `Name`, see `reify` in
+`Language.Haskell.TH`.
+
+# Error Message
+```
+Example.hs:9:17: error: [GHC-18157]
+    GHC stage restriction:
+      ‘foo’ is used in a top-level splice, quasi-quote, or annotation,
+      and must be imported, not defined locally
+  |
+9 | doSomethingWith foo
+  |                 ^^^
+```