+-- | Given a data constructor in the heap, find its Name.
+-- The info tables for data constructors have a field which records
+-- the source name of the constructor as a Ptr Word8 (UTF-8 encoded
+-- string). The format is:
+--
+-- Package:Module.Name
+--
+-- We use this string to lookup the interpreter's internal representation of the name
+-- using the lookupOrig.
+
+dataConInfoPtrToName :: Ptr () -> TcM Name
+dataConInfoPtrToName x = do
+ theString <- ioToTcRn $ do
+ let ptr = castPtr x :: Ptr StgInfoTable
+ conDescAddress <- getConDescAddress ptr
+ peekArray0 0 conDescAddress
+ let (pkg, mod, occ) = parse theString
+ pkgFS = mkFastStringByteList pkg
+ modFS = mkFastStringByteList mod
+ occFS = mkFastStringByteList occ
+ occName = mkOccNameFS OccName.dataName occFS
+ modName = mkModule (fsToPackageId pkgFS) (mkModuleNameFS modFS)
+ lookupOrig modName occName
+
+ where
+
+ {- To find the string in the constructor's info table we need to consider
+ the layout of info tables relative to the entry code for a closure.
+
+ An info table can be next to the entry code for the closure, or it can
+ be separate. The former (faster) is used in registerised versions of ghc,
+ and the latter (portable) is for non-registerised versions.
+
+ The diagrams below show where the string is to be found relative to
+ the normal info table of the closure.
+
+ 1) Code next to table:
+
+ --------------
+ | | <- pointer to the start of the string
+ --------------
+ | | <- the (start of the) info table structure
+ | |
+ | |
+ --------------
+ | entry code |
+ | .... |
+
+ In this case the pointer to the start of the string can be found in
+ the memory location _one word before_ the first entry in the normal info
+ table.
+
+ 2) Code NOT next to table:
+
+ --------------
+ info table structure -> | *------------------> --------------
+ | | | entry code |
+ | | | .... |
+ --------------
+ ptr to start of str -> | |
+ --------------
+
+ In this case the pointer to the start of the string can be found
+ in the memory location: info_table_ptr + info_table_size
+ -}
+
+ getConDescAddress :: Ptr StgInfoTable -> IO (Ptr Word8)
+ getConDescAddress ptr = do
+#ifdef GHCI_TABLES_NEXT_TO_CODE
+ offsetToString <- peek $ ptr `plusPtr` (- wORD_SIZE)
+ return $ (ptr `plusPtr` stdInfoTableSizeB) `plusPtr` (fromIntegral (offsetToString :: StgWord))
+#else
+ peek $ intPtrToPtr $ (ptrToIntPtr ptr) + stdInfoTableSizeB
+#endif