Add --exclude flag to nix search

If a package's attribute path, description or name contains matches for any of the
regexes specified via `-e` or `--exclude` that package is excluded from
the final output.

src/nix/search.cc

@@ -18,16 +18,24 @@ using namespace nix;
 
 std::string wrap(std::string prefix, std::string s)
 {
-    return prefix + s + ANSI_NORMAL;
+    return concatStrings(prefix, s, ANSI_NORMAL);
 }
 
 struct CmdSearch : InstallableCommand, MixJSON
 {
     std::vector<std::string> res;
+    std::vector<std::string> excludeRes;
 
     CmdSearch()
     {
         expectArgs("regex", &res);
+        addFlag(Flag {
+            .longName = "exclude",
+            .shortName = 'e',
+            .description = "Hide packages whose attribute path, name or description contain *regex*.",
+            .labels = {"regex"},
+            .handler = Handler(&excludeRes),
+        });
     }
 
     std::string description() override
@@ -62,11 +70,16 @@ struct CmdSearch : InstallableCommand, MixJSON
             res.push_back("^");
 
         std::vector<std::regex> regexes;
+        std::vector<std::regex> excludeRegexes;
         regexes.reserve(res.size());
+        excludeRegexes.reserve(excludeRes.size());
 
         for (auto & re : res)
             regexes.push_back(std::regex(re, std::regex::extended | std::regex::icase));
 
+        for (auto & re : excludeRes)
+            excludeRegexes.emplace_back(re, std::regex::extended | std::regex::icase);
+
         auto state = getEvalState();
 
         auto jsonOut = json ? std::make_unique<JSONObject>(std::cout) : nullptr;
@@ -106,6 +119,14 @@ struct CmdSearch : InstallableCommand, MixJSON
                     std::vector<std::smatch> nameMatches;
                     bool found = false;
 
+                    for (auto & regex : excludeRegexes) {
+                        if (
+                            std::regex_search(attrPath2, regex)
+                            || std::regex_search(name.name, regex)
+                            || std::regex_search(description, regex))
+                            return;
+                    }
+
                     for (auto & regex : regexes) {
                         found = false;
                         auto addAll = [&found](std::sregex_iterator it, std::vector<std::smatch> & vec) {

src/nix/search.md

@@ -43,12 +43,23 @@ R""(
   # nix search nixpkgs 'firefox|chromium'
   ```
 
-* Search for packages containing `git'`and either `frontend` or `gui`:
+* Search for packages containing `git` and either `frontend` or `gui`:
 
   ```console
   # nix search nixpkgs git 'frontend|gui'
   ```
 
+* Search for packages containing `neovim` but hide ones containing either `gui` or `python`:
+
+  ```console
+  # nix search nixpkgs neovim -e 'python|gui'
+  ```
+  or
+
+  ```console
+  # nix search nixpkgs neovim -e 'python' -e 'gui'
+  ```
+
 # Description
 
 `nix search` searches *installable* (which must be evaluatable, e.g. a