8 files changed, 99 insertions, 24 deletions
diff --git a/src/libutil/position.cc b/src/libutil/position.cc
index b39a5a1d4..724e560b7 100644
--- a/src/libutil/position.cc
+++ b/src/libutil/position.cc
@@ -29,32 +29,17 @@ std::optional<LinesOfCode> Pos::getCodeLines() const
         return std::nullopt;
 
     if (auto source = getSource()) {
-
-        std::istringstream iss(*source);
-        // count the newlines.
-        int count = 0;
-        std::string curLine;
-        int pl = line - 1;
-
+        LinesIterator lines(*source), end;
         LinesOfCode loc;
 
-        do {
-            std::getline(iss, curLine);
-            ++count;
-            if (count < pl)
-                ;
-            else if (count == pl) {
-                loc.prevLineOfCode = curLine;
-            } else if (count == pl + 1) {
-                loc.errLineOfCode = curLine;
-            } else if (count == pl + 2) {
-                loc.nextLineOfCode = curLine;
-                break;
-            }
-
-            if (!iss.good())
-                break;
-        } while (true);
+        if (line > 1)
+            std::advance(lines, line - 2);
+        if (lines != end && line > 1)
+            loc.prevLineOfCode = *lines++;
+        if (lines != end)
+            loc.errLineOfCode = *lines++;
+        if (lines != end)
+            loc.nextLineOfCode = *lines++;
 
         return loc;
     }
@@ -109,4 +94,26 @@ std::ostream & operator<<(std::ostream & str, const Pos & pos)
     return str;
 }
 
+void Pos::LinesIterator::bump(bool atFirst)
+{
+    if (!atFirst) {
+        pastEnd = input.empty();
+        if (!input.empty() && input[0] == '\r')
+            input.remove_prefix(1);
+        if (!input.empty() && input[0] == '\n')
+            input.remove_prefix(1);
+    }
+
+    // nix line endings are not only \n as eg std::getline assumes, but also
+    // \r\n **and \r alone**. not treating them all the same causes error
+    // reports to not match with line numbers as the parser expects them.
+    auto eol = input.find_first_of("\r\n");
+
+    if (eol > input.size())
+        eol = input.size();
+
+    curLine = input.substr(0, eol);
+    input.remove_prefix(eol);
+}
+
 }
diff --git a/src/libutil/position.hh b/src/libutil/position.hh
index a184997ed..9bdf3b4b5 100644
--- a/src/libutil/position.hh
+++ b/src/libutil/position.hh
@@ -67,6 +67,48 @@ struct Pos
     bool operator==(const Pos & rhs) const = default;
     bool operator!=(const Pos & rhs) const = default;
     bool operator<(const Pos & rhs) const;
+
+    struct LinesIterator {
+        using difference_type = size_t;
+        using value_type = std::string_view;
+        using reference = const std::string_view &;
+        using pointer = const std::string_view *;
+        using iterator_category = std::input_iterator_tag;
+
+        LinesIterator(): pastEnd(true) {}
+        explicit LinesIterator(std::string_view input): input(input), pastEnd(input.empty()) {
+            if (!pastEnd)
+                bump(true);
+        }
+
+        LinesIterator & operator++() {
+            bump(false);
+            return *this;
+        }
+        LinesIterator operator++(int) {
+            auto result = *this;
+            ++*this;
+            return result;
+        }
+
+        reference operator*() const { return curLine; }
+        pointer operator->() const { return &curLine; }
+
+        bool operator!=(const LinesIterator & other) const {
+            return !(*this == other);
+        }
+        bool operator==(const LinesIterator & other) const {
+            return (pastEnd && other.pastEnd)
+                || (std::forward_as_tuple(input.size(), input.data())
+                    == std::forward_as_tuple(other.input.size(), other.input.data()));
+        }
+
+    private:
+        std::string_view input, curLine;
+        bool pastEnd = false;
+
+        void bump(bool atFirst);
+    };
 };
 
 std::ostream & operator<<(std::ostream & str, const Pos & pos);
diff --git a/tests/functional/lang/eval-fail-eol-1.err.exp b/tests/functional/lang/eval-fail-eol-1.err.exp
new file mode 100644
index 000000000..3f5a5c22c
--- /dev/null
+++ b/tests/functional/lang/eval-fail-eol-1.err.exp
@@ -0,0 +1,6 @@
+error: undefined variable 'invalid'
+       at /pwd/lang/eval-fail-eol-1.nix:2:1:
+            1| # foo
+            2| invalid
+             | ^
+            3| # bar
diff --git a/tests/functional/lang/eval-fail-eol-1.nix b/tests/functional/lang/eval-fail-eol-1.nix
new file mode 100644
index 000000000..476223919
--- /dev/null
+++ b/tests/functional/lang/eval-fail-eol-1.nix
@@ -0,0 +1,3 @@
+# foo
+invalid
+# bar
diff --git a/tests/functional/lang/eval-fail-eol-2.err.exp b/tests/functional/lang/eval-fail-eol-2.err.exp
new file mode 100644
index 000000000..ff13e2d55
--- /dev/null
+++ b/tests/functional/lang/eval-fail-eol-2.err.exp
@@ -0,0 +1,6 @@
+error: undefined variable 'invalid'
+       at /pwd/lang/eval-fail-eol-2.nix:2:1:
+            1| # foo
+            2| invalid
+             | ^
+            3| # bar
diff --git a/tests/functional/lang/eval-fail-eol-2.nix b/tests/functional/lang/eval-fail-eol-2.nix
new file mode 100644
index 000000000..0cf92a425
--- /dev/null
+++ b/tests/functional/lang/eval-fail-eol-2.nix
@@ -0,0 +1,2 @@
+# foo
+invalid
+# bar
diff --git a/tests/functional/lang/eval-fail-eol-3.err.exp b/tests/functional/lang/eval-fail-eol-3.err.exp
new file mode 100644
index 000000000..ada3c5ecd
--- /dev/null
+++ b/tests/functional/lang/eval-fail-eol-3.err.exp
@@ -0,0 +1,6 @@
+error: undefined variable 'invalid'
+       at /pwd/lang/eval-fail-eol-3.nix:2:1:
+            1| # foo
+            2| invalid
+             | ^
+            3| # bar
diff --git a/tests/functional/lang/eval-fail-eol-3.nix b/tests/functional/lang/eval-fail-eol-3.nix
new file mode 100644
index 000000000..33422452d
--- /dev/null
+++ b/tests/functional/lang/eval-fail-eol-3.nix
@@ -0,0 +1,3 @@
+# foo
+invalid
+# bar