From 31e3f332ea027ec516ec94d034a8763c153ac6cb Mon Sep 17 00:00:00 2001
From: Matthew Pickering <matthewtpickering@gmail.com>
Date: Tue, 16 Sep 2025 16:52:06 +0100
Subject: [PATCH] Expand ${pkgroot} variable when reading haddock-html field
 from ghc-pkg

This fixes #11217

No test, as it is difficult to test since you need to:

1. Ensure there is a package registration with ${pkgroot}
2. Check the existence of a certain link in the generated HTML.
---
 Cabal/src/Distribution/Simple/Program/HcPkg.hs | 2 +-
 changelog.d/pr-11218.md                        | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)
 create mode 100644 changelog.d/pr-11218.md

diff --git a/Cabal/src/Distribution/Simple/Program/HcPkg.hs b/Cabal/src/Distribution/Simple/Program/HcPkg.hs
index a494bc63f02..7ad7eba4ebc 100644
--- a/Cabal/src/Distribution/Simple/Program/HcPkg.hs
+++ b/Cabal/src/Distribution/Simple/Program/HcPkg.hs
@@ -351,7 +351,7 @@ mungePackagePaths pkgroot pkginfo =
     , libraryDynDirs = mungePaths (libraryDynDirs pkginfo)
     , frameworkDirs = mungePaths (frameworkDirs pkginfo)
     , haddockInterfaces = mungePaths (haddockInterfaces pkginfo)
-    , haddockHTMLs = mungeUrls (haddockHTMLs pkginfo)
+    , haddockHTMLs = mungePaths (mungeUrls (haddockHTMLs pkginfo))
     }
   where
     mungePaths = map mungePath
diff --git a/changelog.d/pr-11218.md b/changelog.d/pr-11218.md
new file mode 100644
index 00000000000..5b69bbb59ee
--- /dev/null
+++ b/changelog.d/pr-11218.md
@@ -0,0 +1,6 @@
+synopsis: Fix links to installed documentation when running `cabal haddock`
+packages: Cabal
+prs: #11218
+
+Links to installed documentation (i.e. for base) from generated haddock should
+now work.