Include provenance in Backpack unfilled requirements error

jappeace-sloth · jappeace · commit 5953eb356360 · 2026-03-17T23:22:24.000+01:00
When a non-library component has unfilled Backpack signature requirements, the error message now shows where each requirement came from (e.g. "brought into scope by build-depends: Fail1") using the ModuleSource information already available in the ModuleScope. Updated the Fail3 test golden files and strengthened the test assertion to verify provenance information is present. Addresses #7192 run fourmalou
diff --git a/Cabal/src/Distribution/Backpack/LinkedComponent.hs b/Cabal/src/Distribution/Backpack/LinkedComponent.hs
@@ -258,7 +258,17 @@ toLinkedComponent
         hang
           (text "Non-library component has unfilled requirements:")
           4
-          (vcat [pretty req | req <- Set.toList reqs])
+          ( vcat
+              [ case Map.lookup req (modScopeRequires linked_shape0) of
+                  Just srcs@(_ : _) ->
+                    hang
+                      (pretty req)
+                      4
+                      (vcat [text "brought into scope by" <+> dispModuleSource (getSource src) | src <- srcs])
+                  _ -> pretty req
+              | req <- Set.toList reqs
+              ]
+          )
 
     -- NB: do NOT include hidden modules here: GHC 7.10's ghc-pkg
     -- won't allow it (since someone could directly synthesize
diff --git a/cabal-testsuite/PackageTests/Backpack/Fail3/setup.cabal.out b/cabal-testsuite/PackageTests/Backpack/Fail3/setup.cabal.out
@@ -1,5 +1,6 @@
 # Setup configure
 Configuring Fail1-0.1.0.0...
 Error:
-    Non-library component has unfilled requirements: UnfilledSig
+    Non-library component has unfilled requirements:
+        UnfilledSig brought into scope by build-depends: Fail1
     In the stanza executable foo
diff --git a/cabal-testsuite/PackageTests/Backpack/Fail3/setup.out b/cabal-testsuite/PackageTests/Backpack/Fail3/setup.out
@@ -1,5 +1,6 @@
 # Setup configure
 Configuring Fail1-0.1.0.0...
 Error:
-    Non-library component has unfilled requirements: UnfilledSig
+    Non-library component has unfilled requirements:
+        UnfilledSig brought into scope by build-depends: Fail1
     In the stanza executable foo
diff --git a/cabal-testsuite/PackageTests/Backpack/Fail3/setup.test.hs b/cabal-testsuite/PackageTests/Backpack/Fail3/setup.test.hs
@@ -3,4 +3,5 @@ main = setupAndCabalTest $ do
     skipUnlessGhcVersion ">= 8.1"
     r <- fails $ setup' "configure" []
     assertOutputContains "UnfilledSig" r
+    assertOutputContains "brought into scope by" r
     return ()
diff --git a/cabal-testsuite/PackageTests/Backpack/Fail4/Fail4.cabal b/cabal-testsuite/PackageTests/Backpack/Fail4/Fail4.cabal
@@ -0,0 +1,24 @@
+cabal-version:       3.0
+name:                Fail4
+version:             0.1.0.0
+license:             BSD-3-Clause
+author:              Edward Z. Yang
+maintainer:          ezyang@cs.stanford.edu
+build-type:          Simple
+
+library sig-lib-a
+  signatures:          UnfilledSig
+  build-depends:       base
+  hs-source-dirs:      lib-a
+  default-language:    Haskell2010
+
+library sig-lib-b
+  signatures:          UnfilledSig
+  build-depends:       base
+  hs-source-dirs:      lib-b
+  default-language:    Haskell2010
+
+executable foo
+  build-depends:       Fail4:sig-lib-a, Fail4:sig-lib-b
+  main-is:             Main.hs
+  default-language:    Haskell2010
diff --git a/cabal-testsuite/PackageTests/Backpack/Fail4/Main.hs b/cabal-testsuite/PackageTests/Backpack/Fail4/Main.hs
@@ -0,0 +1 @@
+main = return ()
diff --git a/cabal-testsuite/PackageTests/Backpack/Fail4/lib-a/UnfilledSig.hsig b/cabal-testsuite/PackageTests/Backpack/Fail4/lib-a/UnfilledSig.hsig
@@ -0,0 +1 @@
+signature UnfilledSig where
diff --git a/cabal-testsuite/PackageTests/Backpack/Fail4/lib-b/UnfilledSig.hsig b/cabal-testsuite/PackageTests/Backpack/Fail4/lib-b/UnfilledSig.hsig
@@ -0,0 +1 @@
+signature UnfilledSig where
diff --git a/cabal-testsuite/PackageTests/Backpack/Fail4/setup.cabal.out b/cabal-testsuite/PackageTests/Backpack/Fail4/setup.cabal.out
@@ -0,0 +1,8 @@
+# Setup configure
+Configuring Fail4-0.1.0.0...
+Error:
+    Non-library component has unfilled requirements:
+        UnfilledSig
+            brought into scope by build-depends: Fail4:sig-lib-a
+            brought into scope by build-depends: Fail4:sig-lib-b
+    In the stanza executable foo
diff --git a/cabal-testsuite/PackageTests/Backpack/Fail4/setup.out b/cabal-testsuite/PackageTests/Backpack/Fail4/setup.out
@@ -0,0 +1,8 @@
+# Setup configure
+Configuring Fail4-0.1.0.0...
+Error:
+    Non-library component has unfilled requirements:
+        UnfilledSig
+            brought into scope by build-depends: Fail4:sig-lib-a
+            brought into scope by build-depends: Fail4:sig-lib-b
+    In the stanza executable foo
diff --git a/cabal-testsuite/PackageTests/Backpack/Fail4/setup.test.hs b/cabal-testsuite/PackageTests/Backpack/Fail4/setup.test.hs
@@ -0,0 +1,8 @@
+import Test.Cabal.Prelude
+main = setupAndCabalTest $ do
+    skipUnlessGhcVersion ">= 8.1"
+    r <- fails $ setup' "configure" []
+    assertOutputContains "UnfilledSig" r
+    assertOutputContains "brought into scope by build-depends: Fail4:sig-lib-a" r
+    assertOutputContains "brought into scope by build-depends: Fail4:sig-lib-b" r
+    return ()
