add trace test; error formatting refinements

src/libutil/error.cc

@@ -185,6 +185,31 @@ void printCodeLines(std::ostream &out,
     }
 }
 
+void printAtPos(const string &prefix, const ErrPos &pos, std::ostream &out)
+{
+    {
+        switch (pos.origin) {
+            case foFile: {
+                out << prefix << ANSI_BLUE << "at: " << ANSI_YELLOW << showErrPos(pos) <<
+                    ANSI_BLUE << " in file: " << ANSI_NORMAL << pos.file;
+                break;
+            }
+            case foString: {
+                out << prefix << ANSI_BLUE << "at: " << ANSI_YELLOW << showErrPos(pos) <<
+                    ANSI_BLUE << " from command line argument" << ANSI_NORMAL;
+                break;
+            }
+            case foStdin: {
+                out << prefix << ANSI_BLUE << "at: " << ANSI_YELLOW << showErrPos(pos) <<
+                    ANSI_BLUE << " from stdin" << ANSI_NORMAL;
+                break;
+            }
+            default:
+                throw Error("invalid FileOrigin in errPos");
+        }
+    }
+}
+
 std::ostream& operator<<(std::ostream &out, const ErrorInfo &einfo)
 {
     auto errwidth = std::max<size_t>(getWindowSize().second, 20);
@@ -240,8 +265,12 @@ std::ostream& operator<<(std::ostream &out, const ErrorInfo &einfo)
         }
     }
 
-    auto ndl = prefix.length() + levelString.length() + 3 + einfo.name.length() + einfo.programName.value_or("").length();
+    auto ndl = prefix.length()
-    auto dashwidth = ndl > (errwidth - 3) ? 3 : errwidth - ndl;
+        + filterANSIEscapes(levelString, true).length()
+        + 7
+        + einfo.name.length()
+        + einfo.programName.value_or("").length();
+    auto dashwidth = std::max<int>(errwidth - ndl, 3);
 
     std::string dashes(dashwidth, '-');
 
@@ -262,29 +291,8 @@ std::ostream& operator<<(std::ostream &out, const ErrorInfo &einfo)
 
     bool nl = false;  // intersperse newline between sections.
     if (einfo.errPos.has_value()) {
-        switch (einfo.errPos->origin) {
-            case foFile: {
         out << prefix << std::endl;
-                auto &pos = *einfo.errPos;
+        printAtPos(prefix, *einfo.errPos, out);
-                out << prefix << ANSI_BLUE << "at: " << ANSI_YELLOW << showErrPos(pos) <<
-                    ANSI_BLUE << " in file: " << ANSI_NORMAL << pos.file;
-                break;
-            }
-            case foString: {
-                out << prefix << std::endl;
-                out << prefix << ANSI_BLUE << "at: " << ANSI_YELLOW << showErrPos(*einfo.errPos) <<
-                    ANSI_BLUE << " from command line argument" << ANSI_NORMAL;
-                break;
-            }
-            case foStdin: {
-                out << prefix << std::endl;
-                out << prefix << ANSI_BLUE << "at: " << ANSI_YELLOW << showErrPos(*einfo.errPos) <<
-                    ANSI_BLUE << " from stdin" << ANSI_NORMAL;
-                break;
-            }
-            default:
-                throw Error("invalid FileOrigin in errPos");
-        }
         nl = true;
     }
 
@@ -320,13 +328,33 @@ std::ostream& operator<<(std::ostream &out, const ErrorInfo &einfo)
     for (auto iter = einfo.traces.rbegin(); iter != einfo.traces.rend(); ++iter)
     {
         try {
-            auto pos = *iter->pos;
             if (nl)
                 out << std::endl << prefix;
-            out << std::endl << prefix;
+
+            const string tracetitle(" show-trace output ");
+
+            int fill = errwidth - tracetitle.length();
+            int lw = 0;
+            int rw = 0;
+            const int min_dashes = 3;
+            if (fill > min_dashes * 2) {
+                if (fill % 2 != 0) {
+                    lw = fill / 2;
+                    rw = lw + 1;
+                }
+                else
+                {
+                    lw = rw = fill / 2;
+                }
+            }
+            else
+                lw = rw = min_dashes;
+
+            out << ANSI_BLUE << std::string(lw, '-') << tracetitle << std::string(rw, '-') << std::endl << prefix;
             out << iter->hint.str() <<  std::endl;
-            out << ANSI_BLUE << "at: " << ANSI_YELLOW << showErrPos(pos) <<
+
-                ANSI_BLUE << " in file: " << ANSI_NORMAL << pos.file  << std::endl;
+            auto pos = *iter->pos;
+            printAtPos(prefix, pos, out);
             nl = true;
             auto loc = getCodeLines(pos);
             if (loc.has_value())

src/libutil/error.hh

@@ -173,6 +173,8 @@ public:
     }
 
     BaseError & addTrace(std::optional<ErrPos> e, hintformat hint);
+
+    bool hasTrace() const { return !err.traces.empty(); }
 };
 
 #define MakeError(newClass, superClass) \

src/libutil/tests/logging.cc

@@ -16,7 +16,7 @@ namespace nix {
         "this is the problem line of code\n"
         "next line of code\n";
     const char *one_liner =
-        "this is the problem line of code";
+        "this is the other problem line of code";
 
     TEST(logEI, catpuresBasicProperties) {
 
@@ -245,6 +245,33 @@ namespace nix {
         ASSERT_STREQ(str.c_str(), "\x1B[33;1mwarning:\x1B[0m\x1B[34;1m --- warning name --- error-unit-test\x1B[0m\n\x1B[34;1mat: \x1B[33;1m(2:13)\x1B[34;1m from stdin\x1B[0m\n\nwarning description\n\n     1| previous line of code\n     2| this is the problem line of code\n      |             \x1B[31;1m^\x1B[0m\n     3| next line of code\n\nthis hint has \x1B[33;1myellow\x1B[0m templated \x1B[33;1mvalues\x1B[0m!!\n");
     }
 
+    /* ----------------------------------------------------------------------------
+     * traces
+     * --------------------------------------------------------------------------*/
+
+    TEST(addTrace, showTracesWithShowTrace) {
+        SymbolTable testTable;
+        auto problem_file = testTable.create(test_file);
+
+        auto oneliner_file = testTable.create(one_liner);
+
+        auto e = AssertionError(ErrorInfo {
+                .name = "wat",
+                .description = "a well-known problem occurred",
+                .hint = hintfmt("it has been %1% days since our last error", "zero"),
+                .errPos = Pos(foString, problem_file, 2, 13),
+            });
+
+        e.addTrace(Pos(foStdin, oneliner_file, 1, 19), "while trying to compute %1%", 42);
+
+        testing::internal::CaptureStderr();
+
+        logError(e.info());
+
+        auto str = testing::internal::GetCapturedStderr();
+        ASSERT_STREQ(str.c_str(), "\x1B[31;1merror:\x1B[0m\x1B[34;1m --- AssertionError --- error-unit-test\x1B[0m\n\x1B[34;1mat: \x1B[33;1m(2:13)\x1B[34;1m from command line argument\x1B[0m\n\na well-known problem occurred\n\n     1| previous line of code\n     2| this is the problem line of code\n      |             \x1B[31;1m^\x1B[0m\n     3| next line of code\n\nit has been \x1B[33;1mzero\x1B[0m days since our last error\n\x1B[34;1m--- show-trace output ---\nwhile trying to compute \x1B[33;1m42\x1B[0m\n\x1B[34;1mat: \x1B[33;1m(1:19)\x1B[34;1m from stdin\x1B[0m\n     1| this is the other problem line of code\n      |                   \x1B[31;1m^\x1B[0m\n");
+    }
+
     /* ----------------------------------------------------------------------------
      * hintfmt
      * --------------------------------------------------------------------------*/