From f97576c5d91d5278155a67e2b8982d2233d4335a Mon Sep 17 00:00:00 2001
From: Ben Burdette <bburdette@gmail.com>
Date: Wed, 3 Jun 2020 14:47:00 -0600
Subject: [PATCH] newline-as-prefix; no final newline in output.

---
 src/libutil/error.cc | 73 +++++++++++++++++++++++---------------------
 1 file changed, 39 insertions(+), 34 deletions(-)

diff --git a/src/libutil/error.cc b/src/libutil/error.cc
index 59628d875..539a7543f 100644
--- a/src/libutil/error.cc
+++ b/src/libutil/error.cc
@@ -57,20 +57,20 @@ void printCodeLines(std::ostream &out, const string &prefix, const NixCode &nixC
 {
     // previous line of code.
     if (nixCode.prevLineOfCode.has_value()) {
-        out << fmt("%1% %|2$5d|| %3%",
-            prefix,
-            (nixCode.errPos.line - 1),
-            *nixCode.prevLineOfCode)
-            << std::endl;
+        out << std::endl 
+            << fmt("%1% %|2$5d|| %3%",
+                prefix,
+                (nixCode.errPos.line - 1),
+                *nixCode.prevLineOfCode);
     }
 
     if (nixCode.errLineOfCode.has_value()) {
         // line of code containing the error.
-        out << fmt("%1% %|2$5d|| %3%",
-            prefix,
-            (nixCode.errPos.line),
-            *nixCode.errLineOfCode)
-            << std::endl;
+        out << std::endl
+            << fmt("%1% %|2$5d|| %3%",
+                prefix,
+                (nixCode.errPos.line),
+                *nixCode.errLineOfCode);
         // error arrows for the column range.
         if (nixCode.errPos.column > 0) {
             int start = nixCode.errPos.column;
@@ -81,20 +81,21 @@ void printCodeLines(std::ostream &out, const string &prefix, const NixCode &nixC
 
             std::string arrows("^");
 
-            out << fmt("%1%      |%2%" ANSI_RED "%3%" ANSI_NORMAL,
-                prefix,
-                spaces,
-                arrows) << std::endl;
+            out << std::endl
+                << fmt("%1%      |%2%" ANSI_RED "%3%" ANSI_NORMAL,
+                    prefix,
+                    spaces,
+                    arrows);
         }
     }
 
     // next line of code.
     if (nixCode.nextLineOfCode.has_value()) {
-        out << fmt("%1% %|2$5d|| %3%",
-            prefix,
-            (nixCode.errPos.line + 1),
-            *nixCode.nextLineOfCode)
-            << std::endl;
+        out << std::endl
+            << fmt("%1% %|2$5d|| %3%",
+                prefix,
+                (nixCode.errPos.line + 1),
+                *nixCode.nextLineOfCode);
     }
 }
 
@@ -167,46 +168,50 @@ std::ostream& operator<<(std::ostream &out, const ErrorInfo &einfo)
             levelString,
             einfo.name,
             dashes,
-            einfo.programName.value_or(""))
-            << std::endl;
+            einfo.programName.value_or(""));
     else
         out << fmt("%1%%2%" ANSI_BLUE " -----%3% %4%" ANSI_NORMAL,
             prefix,
             levelString,
             dashes,
-            einfo.programName.value_or(""))
-            << std::endl;
+            einfo.programName.value_or(""));
 
-    // filename, line, column.
+    bool nl = false;  // intersperse newline between sections.
     if (einfo.nixCode.has_value()) {
         if (einfo.nixCode->errPos.file != "") {
-            out << fmt("%1%in file: " ANSI_BLUE "%2% %3%" ANSI_NORMAL,
+            // filename, line, column.
+            out << std::endl << fmt("%1%in file: " ANSI_BLUE "%2% %3%" ANSI_NORMAL,
                 prefix,
                 einfo.nixCode->errPos.file,
-                showErrPos(einfo.nixCode->errPos)) << std::endl;
-            out << prefix << std::endl;
+                showErrPos(einfo.nixCode->errPos));
         } else {
-            out << fmt("%1%from command line argument", prefix) << std::endl;
-            out << prefix << std::endl;
+            out << std::endl << fmt("%1%from command line argument", prefix);
         }
+        nl = true;
     }
 
     // description
     if (einfo.description != "") {
-        out << prefix << einfo.description << std::endl;
-        out << prefix << std::endl;
+        if (nl)
+            out << std::endl << prefix;
+        out << std::endl << prefix << einfo.description;
+        nl = true;
     }
 
     // lines of code.
     if (einfo.nixCode.has_value() && einfo.nixCode->errLineOfCode.has_value()) {
+        if (nl)
+            out << std::endl << prefix;
         printCodeLines(out, prefix, *einfo.nixCode);
-        out << prefix << std::endl;
+        nl = true;
     }
 
     // hint
     if (einfo.hint.has_value()) {
-        out << prefix << *einfo.hint << std::endl;
-        out << prefix << std::endl;
+        if (nl)
+            out << std::endl << prefix;
+        out << std::endl << prefix << *einfo.hint;
+        nl = true;
     }
 
     return out;