From f158a8d08fd21fb0778593de3dd1426650e844d3 Mon Sep 17 00:00:00 2001
From: Rodrigo Mesquita <rodrigo.m.mesquita@gmail.com>
Date: Thu, 16 Nov 2023 15:38:55 +0000
Subject: [PATCH] Improve error message when reading invalid `.target` files
A `.target` file generated by ghc-toolchain or by configure can become
invalid if the target representation (`Toolchain.Target`) is changed
while the files are not re-generated by calling `./configure` or
`ghc-toolchain` again. There is also the issue of hadrian caching the
dependencies on `.target` files, which makes parsing fail when reading
reading the cached value if the representation has been updated.
This patch provides a better error message in both situations, moving
away from a terrible `Prelude.read: no parse` error that you would get
otherwise.
Fixes #24199
---
hadrian/src/Hadrian/Oracles/TextFile.hs | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/hadrian/src/Hadrian/Oracles/TextFile.hs b/hadrian/src/Hadrian/Oracles/TextFile.hs
index ebdfe31a168b..a85669780d34 100644
--- a/hadrian/src/Hadrian/Oracles/TextFile.hs
+++ b/hadrian/src/Hadrian/Oracles/TextFile.hs
@@ -163,14 +163,23 @@ textFileOracle = do
putVerbose $ "| TargetFile oracle: reading " ++ quote file ++ "..."
mtarget <- readMaybe <$> readFile' file
case mtarget of
- Nothing -> error $ "Failed to read a Toolchain.Target from " ++ quote file
+ Nothing -> error $ unlines ["Error parsing a Toolchain.Target from " ++ quote file,
+ "Perhaps the `.target` file is out of date.",
+ "Try re-running `./configure`."
+ ]
+
Just target -> return (target :: Toolchain.Target)
void $ addOracleCache $ \(TargetFile file) -> tf file
-- Orphan instances for (ShakeValue Toolchain.Target)
instance Binary Toolchain.Target where
- put = put . show
- get = read <$> get
+ put = put . show
+ get = fromMaybe (error $ unlines ["Error parsing a toolchain `.target` file from its binary representation in hadrian.",
+ "This is likely caused by a stale hadrian/shake cache",
+ "which has saved an old `.target` file that can't be parsed",
+ "into a more recent `Toolchain.Target`. It is recommended to reset",
+ "by running `./hadrian/build clean`."
+ ]) . readMaybe <$> get
instance Hashable Toolchain.Target where
hashWithSalt s = hashWithSalt s . show
--
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