Fix #6927 Error when cyclic snapshot locations detected

ChangeLog.md

@@ -25,14 +25,16 @@ Other enhancements:
 
 Bug fixes:
 
-* `stack test --no-rerun-tests` correctly skips test suites that have 
-  previously been built and run successfully, including for non-Backpack 
+* `stack test --no-rerun-tests` correctly skips test suites that have
+  previously been built and run successfully, including for non-Backpack
   packages built by the per-component planner.
-* Stack's per-component build planner correctly handles the cross-package 
-  test/library cycle shape from issue #6905: project package A's library 
-  depending on project package B's library, with B's test suite depending on A, 
+* Stack's per-component build planner correctly handles the cross-package
+  test/library cycle shape from issue #6905: project package A's library
+  depending on project package B's library, with B's test suite depending on A,
   builds in the right order with the right configure flags.
-
+* If snapshot locations are cyclic, Stack reports an error rather than going
+  round in circles.
+
 ##  v3.11.1 - 2026-06-13
 
 **Changes since v3.9.3:**

cabal.config

@@ -146,7 +146,7 @@ constraints:
   , optparse-applicative ==0.18.1.0
   , optparse-simple ==0.1.1.4
   , os-string ==2.0.7
-  , pantry ==0.11.3
+  , pantry ==0.11.4
   , parsec ==3.1.18.0
   , parser-combinators ==1.3.1
   , path ==0.9.6

doc/topics/custom_snapshot.md

@@ -73,10 +73,10 @@ has changed by hashing the contents of the involved files, and using it to
 identify the snapshot internally. It is often reasonably efficient to modify a
 custom snapshot, due to Stack sharing snapshot packages whenever possible.
 
-!!! warning "Cyclic snapshot locations"
+!!! note "Cyclic snapshot locations"
 
-    If snapshot locations form a cycle, Stack will not detect this but will go
-    round in circles and appear to hang.
+    If Stack detects that snapshot locations form a cycle, it will report an
+    error.
 
 ### Overriding the compiler
 

doc/topics/snapshot_location.md

@@ -128,10 +128,10 @@ There are four ways to specify a snapshot location:
 
     This allows local file paths and covenience synonyms to be disambiguated.
 
-!!! warning "Cyclic snapshot locations"
+!!! note "Cyclic snapshot locations"
 
-    If snapshot locations form a cycle, Stack will not detect this but will go
-    round in circles and appear to hang.
+    If Stack detects that snapshot locations form a cycle, it will report an
+    error.
 
 ## At the command line
 

package.yaml

@@ -105,7 +105,7 @@ dependencies:
 - neat-interpolation
 - open-browser
 - optparse-applicative >= 0.18.1.0
-- pantry >= 0.11.3
+- pantry >= 0.11.4
 - path >= 0.9.5
 - path-io
 # In order for Cabal (the tool) to build Stack, it needs to be told of the

stack.yaml

@@ -39,7 +39,9 @@ extra-deps:
 # lts-24.43 specifies open-browser-0.4.0.0
 - open-browser-0.5.1.0@sha256:0dc8dc33b9bba0e025e444355f6c2d806f62a4656446961c3647165f80f0d278,1959
 # lts-24.43 specifies pantry-0.10.1
-- pantry-0.11.3@sha256:96fa2c7fa6cee9e470f984da567492f6bfaee058d14c1456f4f79b68a78d7be2,7668
+# We refer to the pull request at the pantry repository while testing Stack:
+- github: commercialhaskell/pantry
+  commit: 7eae6adc4583f1cedb33f115a6396dfa78b57bb9
 # lts-24.43 specifies persistent-2.17.1.0
 - persistent-2.18.1.0@sha256:6a111b26c3e710f1e080a7543cf93766c4cc53ac560dbaa0d4b7ddc98a2f7b1d,7096
 # lts-24.43 excludes ram

stack.yaml.lock

@@ -138,12 +138,16 @@ packages:
   original:
     hackage: open-browser-0.5.1.0@sha256:0dc8dc33b9bba0e025e444355f6c2d806f62a4656446961c3647165f80f0d278,1959
 - completed:
-    hackage: pantry-0.11.3@sha256:96fa2c7fa6cee9e470f984da567492f6bfaee058d14c1456f4f79b68a78d7be2,7668
+    name: pantry
     pantry-tree:
-      sha256: bedd749e9cfdb8adb1a253b34a3350aa89f5ca903aa341579351ce0a937af1f5
-      size: 2722
+      sha256: e9326d0cbb8e33197d4008bcedb61061b39ab820562cdbcb4bd07216af1a556f
+      size: 3763
+    sha256: c41520e493e14baef2bdf14b529be1c13c3ee2a7055adffa3f1fbd8139d6d59f
+    size: 116083
+    url: https://github.com/commercialhaskell/pantry/archive/7eae6adc4583f1cedb33f115a6396dfa78b57bb9.tar.gz
+    version: 0.11.4
   original:
-    hackage: pantry-0.11.3@sha256:96fa2c7fa6cee9e470f984da567492f6bfaee058d14c1456f4f79b68a78d7be2,7668
+    url: https://github.com/commercialhaskell/pantry/archive/7eae6adc4583f1cedb33f115a6396dfa78b57bb9.tar.gz
 - completed:
     hackage: persistent-2.18.1.0@sha256:6a111b26c3e710f1e080a7543cf93766c4cc53ac560dbaa0d4b7ddc98a2f7b1d,7096
     pantry-tree:

tests/integration/tests/6927-cyclic-snapshots/Main.hs

@@ -0,0 +1,32 @@
+-- | Stack detects when snapshot locations form a cycle and reports an error.
+--
+-- See: https://github.com/commercialhaskell/stack/issues/6927
+
+import           Control.Monad ( unless )
+import           Data.List ( isInfixOf )
+import           StackTest
+
+main :: IO ()
+main = do
+  -- `stack build` makes use of pantry's loadAndCompleteSnapshotRaw':
+  stackErrStderr
+    ["--stack-yaml", "stack1.yaml", "build"]
+    (expectMessage cycleDetected)
+  stackErrStderr
+    ["--stack-yaml", "stack2.yaml", "build"]
+    (expectMessage cycleDetected)
+  -- `stack --snapshot <snapshot> list` makes use of pantry's loadSnapshot:
+  stackErrStderr
+    ["--snapshot", "my-snapshot.yaml", "list", "base"]
+    (expectMessage cycleDetected)
+  stackErrStderr
+    ["--snapshot", "my-snapshot1.yaml", "list", "base"]
+    (expectMessage cycleDetected)
+
+cycleDetected :: String
+cycleDetected = "Cycle detected while reading snapshot."
+
+expectMessage :: String -> String -> IO ()
+expectMessage msg stderr =
+ unless (words msg `isInfixOf` words stderr) $
+   error $ "Expected:\n\n" <> msg <> "\n\nin stderr, got:\n\n" <> stderr

tests/integration/tests/6927-cyclic-snapshots/files/.gitignore

@@ -0,0 +1 @@
+myPackage.cabal

tests/integration/tests/6927-cyclic-snapshots/files/my-snapshot.yaml

@@ -0,0 +1,4 @@
+name: my-snapshot
+
+# In error, refers to itself:
+snapshot: my-snapshot.yaml

tests/integration/tests/6927-cyclic-snapshots/files/my-snapshot1.yaml

@@ -0,0 +1,3 @@
+name: my-snapshot1
+
+snapshot: my-snapshot2.yaml

tests/integration/tests/6927-cyclic-snapshots/files/my-snapshot2.yaml

@@ -0,0 +1,3 @@
+name: my-snapshot2
+
+snapshot: my-snapshot3.yaml

tests/integration/tests/6927-cyclic-snapshots/files/my-snapshot3.yaml

@@ -0,0 +1,4 @@
+name: my-snapshot3
+
+# In error, refers to my-snapshot1, creating a cycle:
+snapshot: my-snapshot4.yaml

tests/integration/tests/6927-cyclic-snapshots/files/my-snapshot4.yaml

@@ -0,0 +1,4 @@
+name: my-snapshot4
+
+# In error, refers to my-snapshot2, creating a cycle:
+snapshot: my-snapshot2.yaml

tests/integration/tests/6927-cyclic-snapshots/files/package.yaml

@@ -0,0 +1,9 @@
+spec-version: 0.36.0
+
+name: myPackage
+
+dependencies:
+- base
+
+library:
+  source-dirs: src

tests/integration/tests/6927-cyclic-snapshots/files/src/Lib.hs

@@ -0,0 +1 @@
+module Lib where

tests/integration/tests/6927-cyclic-snapshots/files/stack1.yaml

@@ -0,0 +1 @@
+snapshot: my-snapshot.yaml

tests/integration/tests/6927-cyclic-snapshots/files/stack2.yaml

@@ -0,0 +1 @@
+snapshot: my-snapshot1.yaml