Add a changelog

Author: philderbeast

changelog.d/pr-10684.md

@@ -0,0 +1,74 @@
+---
+synopsis: "A project target is required for the REPL command"
+packages: [cabal-install]
+prs: 10684
+issues: 10527
+---
+
+With a project, the REPL command requires a target. If one is not given then a
+message is shown explaining this and naming the project if the `--project-file`
+option was given (but not when the default 'cabal.project' project name is used
+implicitly).  We're not yet able to list project targets so in the meantime, the
+messages lists the packages of the project.
+
+* When the implicit default `cabal.project` is used:
+
+```
+$ cat cabal.project
+packages: pkg-one pkg-two
+
+$ cabal repl
+Error: [Cabal-7076]
+With a project, the REPL command requires a single target. The packages in this project are:
+ - pkg-one
+ - pkg-two
+```
+
+* When the `--project-file` option is used, the file name is included:
+
+```
+$ cat some.project 
+packages: pkg-one pkg-two
+
+$ cabal repl --project-file=some.project
+...
+Error: [Cabal-7076]
+With a project, the REPL command requires a single target. The packages in this project, 'some.project', are:
+ - pkg-one
+ - pkg-two
+```
+
+* When the project has no packages, this is mentioned in the message:
+
+```
+$ cat empty.project
+
+$ cabal repl --project-file=empty.project
+...
+Error: [Cabal-7076]
+With a project, the REPL command requires a single target but there are no
+packages in this project, 'empty.project', to choose a package (library) or
+other component from as the target for this command.
+```
+
+* Before the fix the message mentioned a `fake-package-0`. This was confusing:
+
+```
+$ ~/.ghcup/bin/cabal-3.12.1.0 repl --project-file=some.project
+...
+Error: [Cabal-7076]
+Internal error when trying to open a repl for the package fake-package-0. The
+package is not in the set of available targets for the project plan, which would
+suggest an inconsistency between readTargetSelectors and resolveTargets.
+```
+
+* Earlier `cabal-install:exe:cabal` versions mentioned using `all` as the target
+  but this won't work for the REPL command:
+
+```
+$ ~/.ghcup/bin/cabal-3.10.3.0 repl --project-file=some.project
+Error: cabal-3.10.3.0: No targets given and there is no package in the current
+directory. Use the target 'all' for all packages in the project or specify
+packages or components by name or location. See 'cabal build --help' for more
+details on target options.
+```