new(cabal-install-internal): Create API for cabal-install

.github/workflows/bootstrap.yml

@@ -49,8 +49,8 @@ jobs:
           # without this the caches of branches with different local package
           # versions (e.g. master vs a release branch) collide and a stale
           # _build/packages.conf gets restored. See #12311.
-          key: bootstrap-${{ steps.get-osver.outputs.osver }}-${{ matrix.ghc }}-${{ hashFiles(format('bootstrap/linux-{0}.json', matrix.ghc), 'Cabal/Cabal.cabal', 'Cabal-syntax/Cabal-syntax.cabal', 'Cabal-hooks/Cabal-hooks.cabal', 'hooks-exe/hooks-exe.cabal', 'cabal-install-solver/cabal-install-solver.cabal', 'cabal-install/cabal-install.cabal') }}-${{ github.sha }}
-          restore-keys: bootstrap-${{ steps.get-osver.outputs.osver }}-${{ matrix.ghc }}-${{ hashFiles(format('bootstrap/linux-{0}.json', matrix.ghc), 'Cabal/Cabal.cabal', 'Cabal-syntax/Cabal-syntax.cabal', 'Cabal-hooks/Cabal-hooks.cabal', 'hooks-exe/hooks-exe.cabal', 'cabal-install-solver/cabal-install-solver.cabal', 'cabal-install/cabal-install.cabal') }}-
+          key: bootstrap-${{ steps.get-osver.outputs.osver }}-${{ matrix.ghc }}-${{ hashFiles(format('bootstrap/linux-{0}.json', matrix.ghc), 'Cabal/Cabal.cabal', 'Cabal-syntax/Cabal-syntax.cabal', 'Cabal-hooks/Cabal-hooks.cabal', 'hooks-exe/hooks-exe.cabal', 'cabal-install-solver/cabal-install-solver.cabal', 'cabal-install-internal/cabal-install-internal.cabal', 'cabal-install/cabal-install.cabal') }}-${{ github.sha }}
+          restore-keys: bootstrap-${{ steps.get-osver.outputs.osver }}-${{ matrix.ghc }}-${{ hashFiles(format('bootstrap/linux-{0}.json', matrix.ghc), 'Cabal/Cabal.cabal', 'Cabal-syntax/Cabal-syntax.cabal', 'Cabal-hooks/Cabal-hooks.cabal', 'hooks-exe/hooks-exe.cabal', 'cabal-install-solver/cabal-install-solver.cabal', 'cabal-install-internal/cabal-install-internal.cabal', 'cabal-install/cabal-install.cabal') }}-
 
       - uses: haskell-actions/setup@v2
         with:

.github/workflows/check-sdist.yml

@@ -38,7 +38,7 @@ jobs:
         id: setup-haskell
         with:
           ghc-version: ${{ matrix.ghc }}
-          cabal-version: latest
+          cabal-version: 3.18.1.0
 
       - uses: actions/checkout@v7
 

.github/workflows/cmd-help.yml

@@ -16,7 +16,9 @@ on:
       - doc/cmd-v2-hidden-help/**
       - doc/setup-help/**
       - cabal-install/src/Distribution/Client/Cmd*.hs
+      - cabal-install-internal/src/Distribution/Client/Cmd*.hs
       - cabal-install/src/Distribution/Client/Main.hs
+      - cabal-install-internal/src/Distribution/Client/Main.hs
       - cabal-install/src/Distribution/Client/Setup.hs
       - Cabal/src/Distribution/Simple.hs
       - Cabal/src/Distribution/Simple/Setup/**
@@ -33,7 +35,8 @@ jobs:
       - uses: haskell-actions/setup@v2
         with:
           ghc-version: 9.12.2
-          cabal-version: latest
+          # must satisfy the setup-depends of cabal-testsuite, see PR #10251
+          cabal-version: 3.18.1.0
       - run: cabal v2-update
       - name: Cache dependencies
         uses: actions/cache@v6

.github/workflows/format.yml

@@ -17,4 +17,5 @@ jobs:
           Cabal/**/*.hs
           Cabal-syntax/**/*.hs
           cabal-install/**/*.hs
+          cabal-install-internal/**/*.hs
           cabal-validate/**/*.hs

.github/workflows/quick-jobs.yml

@@ -34,7 +34,7 @@ jobs:
         id: setup-haskell
         with:
           ghc-version: ${{ env.GHC_FOR_QUICK_JOBS }}
-          cabal-version: latest
+          cabal-version: 3.18.1.0
       - name: Haskell versions
         run: |
           ghc --version
@@ -80,7 +80,8 @@ jobs:
         id: setup-haskell
         with:
           ghc-version: ${{ env.GHC_FOR_QUICK_JOBS }}
-          cabal-version: latest
+          # must satisfy the setup-depends of cabal-testsuite, see PR #10251
+          cabal-version: 3.18.1.0
       - name: Haskell versions
         run: |
           ghc --version
@@ -128,7 +129,8 @@ jobs:
         id: setup-haskell
         with:
           ghc-version: ${{ env.GHC_FOR_QUICK_JOBS }}
-          cabal-version: latest
+          # must satisfy the setup-depends of cabal-testsuite, see PR #10251
+          cabal-version: 3.18.1.0
       - name: Haskell versions
         run: |
           ghc --version
@@ -168,7 +170,7 @@ jobs:
         id: setup-haskell
         with:
           ghc-version: ${{ env.GHC_FOR_QUICK_JOBS }}
-          cabal-version: latest
+          cabal-version: 3.18.1.0
       - name: Haskell versions
         run: |
           ghc --version

.github/workflows/validate.yml

@@ -99,7 +99,7 @@ jobs:
         id: setup-haskell
         with:
           ghc-version: ${{ matrix.ghc }}
-          cabal-version: 3.12.1.0 # see https://github.com/haskell/cabal/pull/10251
+          cabal-version: 3.18.1.0 # see https://github.com/haskell/cabal/pull/10251
           ghcup-release-channel: https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-prereleases-0.0.9.yaml
 
       # runner.os isn't sufficient for binary compatible caches
@@ -267,7 +267,7 @@ jobs:
         id: setup-haskell
         with:
           ghc-version: ${{ env.GHC_FOR_RELEASE }}
-          cabal-version: latest
+          cabal-version: 3.18.1.0
 
       - name: GHC versions
         run: |
@@ -331,7 +331,9 @@ jobs:
         id: setup-haskell
         with:
           ghc-version: ${{ env.GHC_FOR_RELEASE }}
-          cabal-version: latest # latest is mandatory for cabal-testsuite, see https://github.com/haskell/cabal/issues/8133
+          # must satisfy the setup-depends of cabal-testsuite, see PR #10251
+          # (issue #8133 asks for the latest release; this is it as of 2026-09)
+          cabal-version: 3.18.1.0
 
       #  See the following link for a breakdown of the following step
       #  https://github.com/haskell/actions/issues/7#issuecomment-745697160
@@ -418,7 +420,7 @@ jobs:
         id: setup-haskell
         with:
           ghc-version: ${{ matrix.ghc }}
-          cabal-version: latest # default, we are not using it in this job
+          cabal-version: 3.18.1.0
 
       - name: Download cabal executable from workflow artifacts
         uses: actions/download-artifact@v8

Makefile

@@ -53,6 +53,7 @@ FORMAT_DIRS_TODO := \
 check:
 	@cd Cabal && cabal check | grep -q "No errors or warnings could be found in the package."
 	@cd cabal-install && cabal check | grep -q "No errors or warnings could be found in the package."
+	@cd cabal-install-internal && cabal check | grep -q "No errors or warnings could be found in the package."
 	@cd Cabal-syntax && cabal check | grep -q "No errors or warnings could be found in the package."
 	@cd Cabal-hooks && cabal check | grep -q "No errors or warnings could be found in the package."
 	@cd hooks-exe && cabal check | grep -q "No errors or warnings could be found in the package."
@@ -271,7 +272,7 @@ validate-via-docker-old:
 # tags
 .PHONY : tags
 tags: ## Generate editor tags, vim ctags and emacs etags.
-	hasktags -b Cabal-syntax/src Cabal/src Cabal-described/src cabal-install/src cabal-testsuite/src
+	hasktags -b Cabal-syntax/src Cabal/src Cabal-described/src cabal-install/src cabal-install-internal/src cabal-testsuite/src
 
 # bootstrapping
 ##############################################################################

bootstrap/bootstrap.py

@@ -89,6 +89,7 @@ class PackageSource(Enum):
                                     , "Cabal-tests"
                                     , "Cabal-tree-diff"
                                     , "cabal-install-solver"
+                                    , "cabal-install-internal"
                                     , "cabal-install"
                                     , "hooks-exe"
                                     ]

bootstrap/linux-9.10.3.json

@@ -515,31 +515,29 @@
         },
         {
             "cabal_sha256": null,
-            "component": "lib:cabal-install",
+            "component": "lib:cabal-install-internal",
             "flags": [
                 "-git-rev",
                 "-legacy-comparison",
                 "+native-dns"
             ],
-            "package": "cabal-install",
+            "package": "cabal-install-internal",
             "revision": null,
             "source": "local",
             "src_sha256": null,
-            "version": "3.18.1.0"
+            "version": "3.19.0.0"
         },
         {
             "cabal_sha256": null,
             "component": "exe:cabal",
             "flags": [
-                "-git-rev",
-                "-legacy-comparison",
-                "+native-dns"
+                "-git-rev"
             ],
             "package": "cabal-install",
             "revision": null,
             "source": "local",
             "src_sha256": null,
-            "version": "3.18.1.0"
+            "version": "3.19.0.0"
         }
     ]
 }

bootstrap/linux-9.12.4.json

@@ -506,31 +506,29 @@
         },
         {
             "cabal_sha256": null,
-            "component": "lib:cabal-install",
+            "component": "lib:cabal-install-internal",
             "flags": [
                 "-git-rev",
                 "-legacy-comparison",
                 "+native-dns"
             ],
-            "package": "cabal-install",
+            "package": "cabal-install-internal",
             "revision": null,
             "source": "local",
             "src_sha256": null,
-            "version": "3.18.1.0"
+            "version": "3.19.0.0"
         },
         {
             "cabal_sha256": null,
             "component": "exe:cabal",
             "flags": [
-                "-git-rev",
-                "-legacy-comparison",
-                "+native-dns"
+                "-git-rev"
             ],
             "package": "cabal-install",
             "revision": null,
             "source": "local",
             "src_sha256": null,
-            "version": "3.18.1.0"
+            "version": "3.19.0.0"
         }
     ]
 }

bootstrap/linux-9.6.7.json

@@ -517,31 +517,29 @@
         },
         {
             "cabal_sha256": null,
-            "component": "lib:cabal-install",
+            "component": "lib:cabal-install-internal",
             "flags": [
                 "-git-rev",
                 "-legacy-comparison",
                 "+native-dns"
             ],
-            "package": "cabal-install",
+            "package": "cabal-install-internal",
             "revision": null,
             "source": "local",
             "src_sha256": null,
-            "version": "3.18.1.0"
+            "version": "3.19.0.0"
         },
         {
             "cabal_sha256": null,
             "component": "exe:cabal",
             "flags": [
-                "-git-rev",
-                "-legacy-comparison",
-                "+native-dns"
+                "-git-rev"
             ],
             "package": "cabal-install",
             "revision": null,
             "source": "local",
             "src_sha256": null,
-            "version": "3.18.1.0"
+            "version": "3.19.0.0"
         }
     ]
 }

bootstrap/linux-9.8.4.json

@@ -517,31 +517,29 @@
         },
         {
             "cabal_sha256": null,
-            "component": "lib:cabal-install",
+            "component": "lib:cabal-install-internal",
             "flags": [
                 "-git-rev",
                 "-legacy-comparison",
                 "+native-dns"
             ],
-            "package": "cabal-install",
+            "package": "cabal-install-internal",
             "revision": null,
             "source": "local",
             "src_sha256": null,
-            "version": "3.18.1.0"
+            "version": "3.19.0.0"
         },
         {
             "cabal_sha256": null,
             "component": "exe:cabal",
             "flags": [
-                "-git-rev",
-                "-legacy-comparison",
-                "+native-dns"
+                "-git-rev"
             ],
             "package": "cabal-install",
             "revision": null,
             "source": "local",
             "src_sha256": null,
-            "version": "3.18.1.0"
+            "version": "3.19.0.0"
         }
     ]
 }

cabal-install-internal/ChangeLog.md

@@ -0,0 +1,5 @@
+# Revision history for cabal-install-internal
+
+## 3.19.0.0
+
+* Split the internal implementation modules out of `cabal-install` (mirroring the earlier `cabal-install-solver` split). This package provides no stability guarantees.

cabal-install-internal/LICENSE

@@ -0,0 +1,34 @@
+Copyright (c) 2003-2026, Cabal Development Team.
+See the AUTHORS file for the full list of copyright holders.
+
+See */LICENSE for the copyright holders of the subcomponents.
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Isaac Jones nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

cabal-install-internal/Setup.hs

@@ -0,0 +1,4 @@
+import Distribution.Simple
+
+main :: IO ()
+main = defaultMain