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Simon Jakobi pushed to branch wip/sjakobi/multi-caret at Glasgow Haskell Compiler / GHC

Commits:

9591c80d
by Simon Jakobi at 2026-06-11T09:22:32+00:00
```
Shorten some comments as suggested by @sheaf.
```

4 changed files:

compiler/GHC/Tc/Errors/Ppr.hs
compiler/GHC/Tc/Errors/Types.hs
compiler/GHC/Types/Error.hs
compiler/GHC/Utils/Logger.hs

Changes:

@@ -3764,13 +3764,8 @@ instance Diagnostic TcRnMessage where
      TcRnZonkerMessage{} -> []
  -- | The prior occurrences of a duplicated entity, for use as the related
 --- locations of a \"duplicate\" diagnostic. Given all occurrences in ascending
 --- source order with the primary span last, return the earlier ones, omitting
 --- repeated spans and spans that coincide with the primary. Several
 --- occurrences can share a single span -- e.g. duplicate declarations brought
 --- into being by one TH splice -- and repeating the primary span among the
 --- related locations would draw its caret twice and emit it again in the JSON
 --- relatedSpans field.
 +-- locations of a \"duplicate\" diagnostic.
 +--
  -- See Note [Choosing the primary and related spans] in GHC.Types.Error.
  priorOccurrences :: NE.NonEmpty SrcSpan -> [SrcSpan]
  priorOccurrences locs =

compiler/GHC/Tc/Errors/Types.hs

@@ -3981,13 +3981,7 @@ data TcRnMessage where
    TcRnDuplicateDecls :: !OccName -- ^ The name of the declarations
                       -> !(NE.NonEmpty Name)
                          -- ^ The individual declarations, in ascending source
 -                        -- order. The last one is the primary span of the
 -                        -- message; 'diagnosticRelatedLocations' returns the
 -                        -- earlier ones, omitting any that coincide with the
 -                        -- primary span (all occurrences can share one span,
 -                        -- e.g. when spliced by a single TH splice). See
 -                        -- Note [Choosing the primary and related spans]
 -                        -- in GHC.Types.Error.
 +                        -- order.
                       -> TcRnMessage
    {-| TcRnPackageImportsDisabled is an error indicating that an import uses

compiler/GHC/Types/Error.hs

@@ -258,30 +258,14 @@ which GHC's diagnostics are forwarded by HLS: an LSP diagnostic carries a single
    https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#diagnostic
 -How the locations are rendered:
+-
 -  * Related spans are additional to the primary span, not replacements for it.
 -    The spans that receive a caret are @primary :| relatedLocations@ (see
 -    'GHC.Driver.Errors.printMessage' and 'defaultLogActionWithHandles').
+-
 -  * Locations are shown — both as carets and in the @At:@ list below — in
 -    exactly the order the message author gives them: the primary span first,
 -    then 'diagnosticRelatedLocations' as listed. The rendering layer neither
 -    reorders nor deduplicates.
+-
 -  * Not every location can be shown as a caret: carets are optional
 -    (@-fno-diagnostics-show-caret@), and some spans have no source to display
 -    anyway (e.g. GHCi input or TH-generated code). Locations that get no caret
 -    are instead listed under an @At:@ heading ('pprAtLocations'; dropped when it
 -    would name only the primary span, which the header already states).
 -    Every location with a real source position thus appears either as a caret
 -    or in the @At:@ list — only spans without one ('UnhelpfulSpan') are dropped
 -    altogether — so messages need not spell the locations out in their prose.
 -    Carets require 'IO' to read the source, so renderers other than
 -    'GHC.Utils.Logger.decorateDiagnostic' — in particular the pure
 -    'GHC.Utils.Error.pprLocMsgEnvelope', used e.g. when 'show'ing a
 -    'GHC.Types.SourceError.SourceError' and for deferred type errors — list
 -    /all/ the locations under @At:@.
 +Locations are rendered exactly in the order they are provided.
 +Not every location can be shown as a caret:
 +  - carets are optional (@-fno-diagnostics-show-caret@)
 +  - some spans have no source to display anyway (e.g. GHCi input or TH-generated code)
 +  - they require 'IO' to read the source code, so pure code (e.g. 'Show SourceError')
 +    doesn't include them.
++
 +Locations that get no caret are instead listed under an @At:@ heading.
  How a message author should pick and order the spans is the subject of
  Note [Choosing the primary and related spans].
@@ -903,11 +887,9 @@ pprAtLocations primary spans
  -- | When @show_caret@ is set, render carets for the given spans; otherwise
  -- render nothing. Either way, return the real spans that did /not/ get a caret,
 --- so the caller can report those locations textually. A span is missed when
 --- carets are disabled, or when its source is unavailable (an unhelpful span —
 --- dropped here — or unreadable source such as GHCi input or TH-generated code).
 --- The spans are kept in the order they were given in; see Note [The source span
 --- model for diagnostics].
 +-- so the caller can report those locations textually.
 +--
 +-- See Note [The source span model for diagnostics].
  getCaretDiagnostics :: Bool -> MessageClass -> NonEmpty SrcSpan -> IO (SDoc, [RealSrcSpan])
  getCaretDiagnostics show_caret msg_class spans
    | not show_caret = pure (empty, realSpans)

compiler/GHC/Utils/Logger.hs

@@ -479,11 +479,7 @@ decorateDiagnostic logflags msg_class srcSpan msg = addLocations
          _                        -> []
        -- The primary span is always caret'd, with the related spans drawn as
 -      -- additional carets.  Order is the message author's: the primary first,
 -      -- then the related spans as given.  'getCaretDiagnostics' preserves that
 -      -- order and does not deduplicate, so an author must not repeat the primary
 -      -- among the related spans.
 -      -- See Note [The source span model for diagnostics] in GHC.Types.Error.
 +      -- additional carets. See Note [The source span model for diagnostics] in GHC.Types.Error.
        sourceSpans :: NonEmpty SrcSpan
        sourceSpans = srcSpan :| relatedSpans