nix flake show: add the description if it exists

src/nix/flake.cc

@@ -17,6 +17,7 @@
 #include "eval-cache.hh"
 #include "markdown.hh"
 #include "users.hh"
+#include "terminal.hh"
 
 #include <nlohmann/json.hpp>
 #include <iomanip>
@@ -1243,25 +1244,98 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                 auto showDerivation = [&]()
                 {
                     auto name = visitor.getAttr(state->sName)->getString();
+                    std::optional<std::string> description;
+                    if (auto aMeta = visitor.maybeGetAttr(state->sMeta)) {
+                        if (auto aDescription = aMeta->maybeGetAttr(state->sDescription))
+                            description = aDescription->getString();
+                    }
+
                     if (json) {
-                        std::optional<std::string> description;
-                        if (auto aMeta = visitor.maybeGetAttr(state->sMeta)) {
-                            if (auto aDescription = aMeta->maybeGetAttr(state->sDescription))
-                                description = aDescription->getString();
-                        }
                         j.emplace("type", "derivation");
                         j.emplace("name", name);
                         if (description)
                             j.emplace("description", *description);
                     } else {
-                        logger->cout("%s: %s '%s'",
-                            headerPrefix,
+                        auto type =
                             attrPath.size() == 2 && attrPathS[0] == "devShell" ? "development environment" :
                             attrPath.size() >= 2 && attrPathS[0] == "devShells" ? "development environment" :
                             attrPath.size() == 3 && attrPathS[0] == "checks" ? "derivation" :
                             attrPath.size() >= 1 && attrPathS[0] == "hydraJobs" ? "derivation" :
-                            "package",
-                            name);
+                            "package";
+                        if (description && !description->empty()) {
+
+                            // Takes a string and returns the # of characters displayed
+                            auto columnLengthOfString = [](std::string_view s) -> unsigned int {
+                                unsigned int columnCount = 0;
+                                for (auto i = s.begin(); i < s.end();) {
+                                    // Test first character to determine if it is one of
+                                    // treeConn, treeLast, treeLine
+                                    if (*i == -30) {
+                                        i += 3;
+                                        ++columnCount;
+                                    }
+                                    // Escape sequences
+                                    // https://en.wikipedia.org/wiki/ANSI_escape_code
+                                    else if (*i == '\e') {
+                                        // Eat '['
+                                        if (*(++i) == '[') {
+                                            ++i;
+                                            // Eat parameter bytes
+                                            while(*i >= 0x30 && *i <= 0x3f) ++i;
+
+                                            // Eat intermediate bytes
+                                            while(*i >= 0x20 && *i <= 0x2f) ++i;
+
+                                            // Eat final byte
+                                            if(*i >= 0x40 && *i <= 0x73) ++i;
+                                        }
+                                        else {
+                                            // Eat Fe Escape sequence
+                                            if (*i >= 0x40 && *i <= 0x5f) ++i;
+                                        }
+                                    }
+                                    else {
+                                        ++i;
+                                        ++columnCount;
+                                    }
+                                }
+
+                                return columnCount;
+                            };
+
+                            // Maximum length to print
+                            size_t maxLength = getWindowSize().second > 0 ? getWindowSize().second : 80;
+
+                            // Trim the description and only use the first line
+                            auto trimmed = trim(*description);
+                            auto newLinePos = trimmed.find('\n');
+                            auto length = newLinePos != std::string::npos ? newLinePos : trimmed.length();
+
+                            auto beginningOfLine = fmt("%s: %s '%s'", headerPrefix, type, name);
+                            auto line = fmt("%s: %s '%s' - '%s'", headerPrefix, type, name, trimmed.substr(0, length));
+
+                            // If we are already over the maximum length then do not trim
+                            // and don't print the description (preserves existing behavior)
+                            if (columnLengthOfString(beginningOfLine) >= maxLength) {
+                                logger->cout("%s", beginningOfLine);
+                            }
+                            // If the entire line fits then print that
+                            else if (columnLengthOfString(line) < maxLength) {
+                                logger->cout("%s", line);
+                            }
+                            // Otherwise we need to truncate
+                            else {
+                                auto lineLength = columnLengthOfString(line);
+                                auto chopOff = lineLength - maxLength;
+                                line.resize(line.length() - chopOff);
+                                line = line.replace(line.length() - 3, 3, "...");
+
+                                logger->cout("%s", line);
+                            }
+                        }
+                        else {
+                            logger->cout("%s: %s '%s'", headerPrefix, type, name);
+                        }
                     }
                 };
 

tests/functional/flakes/show.sh

@@ -87,3 +87,28 @@ assert show_output.legacyPackages.${builtins.currentSystem}.AAAAAASomeThingsFail
 assert show_output.legacyPackages.${builtins.currentSystem}.simple.name == "simple";
 true
 '
+
+cat >flake.nix<<EOF
+{
+  outputs = inputs: {
+    packages.$system = {
+      aNoDescription = import ./simple.nix;
+      bOneLineDescription = import ./simple.nix // { meta.description = "one line"; };
+      cMultiLineDescription = import ./simple.nix // { meta.description = ''
+         line one
+        line two
+      ''; };
+      dLongDescription = import ./simple.nix // { meta.description = ''
+        01234567890123456789012345678901234567890123456789012345678901234567890123456789abcdefg
+      ''; };
+      eEmptyDescription = import ./simple.nix // { meta.description = ""; };
+    };
+  };
+}
+EOF
+nix flake show > ./show-output.txt
+test "$(awk -F '[:] ' '/aNoDescription/{print $NF}' ./show-output.txt)" = "package 'simple'"
+test "$(awk -F '[:] ' '/bOneLineDescription/{print $NF}' ./show-output.txt)" = "package 'simple' - 'one line'"
+test "$(awk -F '[:] ' '/cMultiLineDescription/{print $NF}' ./show-output.txt)" = "package 'simple' - 'line one'"
+test "$(awk -F '[:] ' '/dLongDescription/{print $NF}' ./show-output.txt)" = "package 'simple' - '012345678901234567890123456..."
+test "$(awk -F '[:] ' '/eEmptyDescription/{print $NF}' ./show-output.txt)" = "package 'simple'"