Merge pull request #9555 from 9999years/positions-in-errors

Pass positions when evaluating

(cherry picked from commit c8458bd731eb1c74159bebe459ea00165e056b65)
Change-Id: I1b4a5d58973be6264ffdb23b4492da200fdb71be

1 files changed, 43 insertions, 0 deletions

diff --git a/doc/manual/rl-next/source-positions-in-errors.md b/doc/manual/rl-next/source-positions-in-errors.md
new file mode 100644
index 000000000..15df884ea
--- /dev/null
+++ b/doc/manual/rl-next/source-positions-in-errors.md
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+synopsis: Source locations are printed more consistently in errors
+issues: #561
+prs: #9555
+description: {
+
+Source location information is now included in error messages more
+consistently. Given this code:
+
+```nix
+let
+  attr = {foo = "bar";};
+  key = {};
+in
+  attr.${key}
+```
+
+Previously, Nix would show this unhelpful message when attempting to evaluate
+it:
+
+```
+error:
+       … while evaluating an attribute name
+
+       error: value is a set while a string was expected
+```
+
+Now, the error message displays where the problematic value was found:
+
+```
+error:
+       … while evaluating an attribute name
+
+         at bad.nix:4:11:
+
+            3|   key = {};
+            4| in attr.${key}
+             |           ^
+            5|
+
+       error: value is a set while a string was expected
+```
+
+}