From c3c068284276d8dbea7bfdd2439ee13e3cef8413 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 28 Sep 2022 17:01:16 +0200
Subject: [PATCH] Don't show "from call site" when we don't know the call site
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This gets rid of stack trace entries like

       … from call site

       at «stdin»:0: (source not available)
---
 src/libexpr/eval.cc    | 3 ++-
 src/libexpr/nixexpr.hh | 6 +++++-
 src/libutil/error.cc   | 4 ++--
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index bfe6c01dd..08ec2fac4 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1617,7 +1617,8 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                         (lambda.name
                             ? concatStrings("'", symbols[lambda.name], "'")
                             : "anonymous lambda"));
-                    addErrorTrace(e, pos, "from call site%s", "");
+                    if (pos != noPos)
+                        addErrorTrace(e, pos, "from call site", "");
                 }
                 throw;
             }
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index 281881543..efd238211 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -52,7 +52,11 @@ public:
 
     explicit operator bool() const { return id > 0; }
 
-    bool operator<(const PosIdx other) const { return id < other.id; }
+    bool operator <(const PosIdx other) const { return id < other.id; }
+
+    bool operator ==(const PosIdx other) const { return id == other.id; }
+
+    bool operator !=(const PosIdx other) const { return id != other.id; }
 };
 
 class PosTable
diff --git a/src/libutil/error.cc b/src/libutil/error.cc
index fa825b2f6..f570dca1d 100644
--- a/src/libutil/error.cc
+++ b/src/libutil/error.cc
@@ -30,12 +30,12 @@ const std::string & BaseError::calcWhat() const
 
 std::optional<std::string> ErrorInfo::programName = std::nullopt;
 
-std::ostream & operator<<(std::ostream & os, const hintformat & hf)
+std::ostream & operator <<(std::ostream & os, const hintformat & hf)
 {
     return os << hf.str();
 }
 
-std::ostream & operator << (std::ostream & str, const AbstractPos & pos)
+std::ostream & operator <<(std::ostream & str, const AbstractPos & pos)
 {
     pos.print(str);
     str << ":" << pos.line;