Highlight manifests from other versions when failing to find packages

base/loading.jl

@@ -1774,9 +1774,10 @@ function __require(into::Module, mod::Symbol)
                     Package $mod not found in current path$hint_message.
                     - $start_sentence `import Pkg; Pkg.add($(repr(String(mod))))` to install the $mod package."""))
             else
+                manifest_warnings = collect_manifest_warnings()
                 throw(ArgumentError("""
                 Package $(where.name) does not have $mod in its dependencies:
-                - You may have a partially installed environment. Try `Pkg.instantiate()`
+                $manifest_warnings- You may have a partially installed environment. Try `Pkg.instantiate()`
                   to ensure all packages in the environment are installed.
                 - Or, if you have $(where.name) checked out for development and have
                   added $mod as a dependency but haven't updated your primary
@@ -1795,6 +1796,55 @@ function __require(into::Module, mod::Symbol)
     end
 end
 
+function find_unsuitable_manifests_versions()
+    unsuitable_manifests = String[]
+    dev_manifests = String[]
+    for env in load_path()
+        project_file = env_project_file(env)
+        project_file isa String || continue # no project file
+        manifest_file = project_file_manifest_path(project_file)
+        manifest_file isa String || continue # no manifest file
+        m = parsed_toml(manifest_file)
+        man_julia_version = get(m, "julia_version", nothing)
+        man_julia_version isa String || @goto mark
+        man_julia_version = VersionNumber(man_julia_version)
+        thispatch(man_julia_version) != thispatch(VERSION) && @goto mark
+        isempty(man_julia_version.prerelease) != isempty(VERSION.prerelease) && @goto mark
+        isempty(man_julia_version.prerelease) && continue
+        man_julia_version.prerelease[1] != VERSION.prerelease[1] && @goto mark
+        if VERSION.prerelease[1] == "DEV"
+            # manifests don't store the 2nd part of prerelease, so cannot check further
+            # so treat them specially in the warning
+            push!(dev_manifests, manifest_file)
+        end
+        continue
+        @label mark
+        push!(unsuitable_manifests, string(manifest_file, " (v", man_julia_version, ")"))
+    end
+    return unsuitable_manifests, dev_manifests
+end
+
+function collect_manifest_warnings()
+    unsuitable_manifests, dev_manifests = find_unsuitable_manifests_versions()
+    msg = ""
+    if !isempty(unsuitable_manifests)
+        msg *= """
+        - Note that the following manifests in the load path were resolved with a different
+          julia version, which may be the cause of the error:
+            $(join(unsuitable_manifests, "\n    "))
+        """
+    end
+    if !isempty(dev_manifests)
+        msg *= """
+        - Note that the following manifests in the load path were resolved a potentially
+          different DEV version of the current version, which may be the cause
+          of the error:
+            $(join(dev_manifests, "\n    "))
+        """
+    end
+    return msg
+end
+
 require(uuidkey::PkgId) = @lock require_lock _require_prelocked(uuidkey)
 
 const REPL_PKGID = PkgId(UUID("3fa0cd96-eef1-5676-8a61-b3b8758bbffb"), "REPL")