lib.fileset: Make error messages more uniform

Just minor changes like:
- Always using "X is a Y, but it should be Z"
- "X is a path that does not exist" rather than "X does not exist"
- Always using multi-line strings for errors
- Always quoting string-like values and not quoting path-like values
  - But do quote filesystem roots. Even though they're paths, they might
    be very small, good to have quotes to know the start/end
- Capitalise the first word
- Distinguish root vs filesystem root more

1 files changed, 4 insertions, 4 deletions

diff --git a/lib/fileset/internal.nix b/lib/fileset/internal.nix
index b919a5de3eef4..853115df9f61d 100644
--- a/lib/fileset/internal.nix
+++ b/lib/fileset/internal.nix
@@ -179,7 +179,7 @@ rec {
           ${context} is of type ${typeOf value}, but it should be a file set or a path instead.''
     else if ! pathExists value then
       throw ''
-        ${context} (${toString value}) does not exist.''
+        ${context} (${toString value}) is a path that does not exist.''
     else
       _singleton value;
 
@@ -208,9 +208,9 @@ rec {
     if firstWithBase != null && differentIndex != null then
       throw ''
         ${functionContext}: Filesystem roots are not the same:
-            ${(head list).context}: root "${toString firstBaseRoot}"
-            ${(elemAt list differentIndex).context}: root "${toString (elemAt filesets differentIndex)._internalBaseRoot}"
-            Different roots are not supported.''
+            ${(head list).context}: Filesystem root is "${toString firstBaseRoot}"
+            ${(elemAt list differentIndex).context}: Filesystem root is "${toString (elemAt filesets differentIndex)._internalBaseRoot}"
+            Different filesystem roots are not supported.''
     else
       filesets;