From a2bf8a66a23ea0f3a63d0cd0a6ed04cd13dce09f Mon Sep 17 00:00:00 2001
From: pennae <github@quasiparticle.net>
Date: Mon, 29 Jan 2024 06:19:23 +0100
Subject: [PATCH] diagnose "unexpected EOF" at EOF

this needs a string comparison because there seems to be no other way to
get that information out of bison. usually the location info is going to
be correct (pointing at a bad token), but since EOF isn't a token as
such it'll be wrong in that this case.

this hasn't shown up much so far because a single line ending *is* a
token, so any file formatted in the usual manner (ie, ending in a line
ending) would have its EOF position reported correctly.
---
 src/libexpr/parser.y                                   | 4 ++++
 tests/functional/lang/parse-fail-eof-in-string.err.exp | 4 ++--
 tests/functional/lang/parse-fail-eof-pos.err.exp       | 5 +++++
 tests/functional/lang/parse-fail-eof-pos.nix           | 2 ++
 4 files changed, 13 insertions(+), 2 deletions(-)
 create mode 100644 tests/functional/lang/parse-fail-eof-pos.err.exp
 create mode 100644 tests/functional/lang/parse-fail-eof-pos.nix

diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 9a543d636..59f088d53 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -64,6 +64,10 @@ using namespace nix;
 
 void yyerror(YYLTYPE * loc, yyscan_t scanner, ParserState * state, const char * error)
 {
+    if (std::string_view(error).starts_with("syntax error, unexpected end of file")) {
+        loc->first_column = loc->last_column;
+        loc->first_line = loc->last_line;
+    }
     throw ParseError({
         .msg = HintFmt(error),
         .pos = state->positions[state->at(*loc)]
diff --git a/tests/functional/lang/parse-fail-eof-in-string.err.exp b/tests/functional/lang/parse-fail-eof-in-string.err.exp
index b28d35950..17f34b62d 100644
--- a/tests/functional/lang/parse-fail-eof-in-string.err.exp
+++ b/tests/functional/lang/parse-fail-eof-in-string.err.exp
@@ -1,5 +1,5 @@
 error: syntax error, unexpected end of file, expecting '"'
-       at «stdin»:3:5:
+       at «stdin»:3:6:
             2| # Note that this file must not end with a newline.
             3| a 1"$
-             |     ^
+             |      ^
diff --git a/tests/functional/lang/parse-fail-eof-pos.err.exp b/tests/functional/lang/parse-fail-eof-pos.err.exp
new file mode 100644
index 000000000..ef9ca381c
--- /dev/null
+++ b/tests/functional/lang/parse-fail-eof-pos.err.exp
@@ -0,0 +1,5 @@
+error: syntax error, unexpected end of file
+       at «stdin»:3:1:
+            2| # no content
+            3|
+             | ^
diff --git a/tests/functional/lang/parse-fail-eof-pos.nix b/tests/functional/lang/parse-fail-eof-pos.nix
new file mode 100644
index 000000000..bd66a2c98
--- /dev/null
+++ b/tests/functional/lang/parse-fail-eof-pos.nix
@@ -0,0 +1,2 @@
+(
+# no content