programName as static member var

src/libutil/error.cc

@@ -1,11 +1,15 @@
 #include "error.hh"
 
 #include <iostream>
+#include <optional>
 
 namespace nix {
 
 using std::cout;
 using std::endl;
+using std::nullopt;
+
+optional<string> ErrorInfo::programName = nullopt;
 
 // return basic_format?
 string showErrLine(ErrLine &errLine)
@@ -98,10 +102,11 @@ void print_error(ErrorInfo &einfo)
       {
         level_string = "wat:";  
         break;
-      }}
+      }
+  }
 
-  int ndl = level_string.length() + 3 + einfo.name.length() + einfo.program.length();
-  int dashwidth = errwidth - 3 ? 3 : 80 - ndl; 
+  int ndl = prefix.length() + level_string.length() + 3 + einfo.name.length() + einfo.programName.value_or("").length();
+  int dashwidth = ndl > (errwidth - 3) ? 3 : 80 - ndl; 
 
   string dashes;
   for (int i = 0; i < dashwidth; ++i)
@@ -114,7 +119,7 @@ void print_error(ErrorInfo &einfo)
     % "---"
     % einfo.name
     % dashes
-    % einfo.program
+    % einfo.programName.value_or("")
     << endl;
 
   // filename.

src/libutil/error.hh

@@ -80,11 +80,12 @@ class ErrorInfo {
     ErrLevel level;
     string name;
     string description;
-    string program;
     optional<NixCode> nixCode;
     string hint;
     ErrorInfo& GetEI() { return *this; }
 
+    static optional<string> programName;
+
     // give these access to the private constructor, 
     // when they are direct descendants.
     friend AddName<ErrorInfo>;
@@ -109,18 +110,21 @@ class ErrorInfo {
 
 };
 
+// Init as error
 class EIError : public ErrorInfo
 {
   protected:
     EIError() : ErrorInfo(elError) {}
 };
 
+// Init as warning
 class EIWarning : public ErrorInfo
 {
   protected:
     EIWarning() : ErrorInfo(elWarning) {}
 };
 
+// Builder class definitions.
 template <class T>
 class AddName : private T
 {

tests/errors/main.cc

@@ -5,11 +5,15 @@
 
 using std::optional;
 using std::nullopt;
+using std::cout;
+using std::endl;
 
 int main() {
 
 using namespace nix; 
 
+  ErrorInfo::programName = optional("errorTest");
+
   /*
   ColumnRange columnRange;
   columnRange.start = 24;