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lang: Turn URL literals into a hard error #15151

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0da728b
tests: fix URL literals in functional tests
Mic92 Feb 4, 2026
d261304
add support for deprecated features
Mic92 Feb 4, 2026
1cee2e7
lang: Turn URL literals into a hard error
Mic92 Feb 4, 2026
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9 changes: 9 additions & 0 deletions doc/manual/generate-dp-features-shortlist.nix
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@@ -0,0 +1,9 @@
with builtins;
with import <nix/utils.nix>;

let
showDeprecatedFeature = name: doc: ''
- [`${name}`](@docroot@/development/deprecated-features.md#dp-feature-${name})
'';
in
dps: indent " " (concatStrings (attrValues (mapAttrs showDeprecatedFeature dps)))
14 changes: 14 additions & 0 deletions doc/manual/generate-dp-features.nix
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@@ -0,0 +1,14 @@
with builtins;
with import <nix/utils.nix>;

let
showDeprecatedFeature =
name: doc:
squash ''
## [`${name}`]{#dp-feature-${name}}
${doc}
'';
in

dps: (concatStringsSep "\n" (attrValues (mapAttrs showDeprecatedFeature dps)))
8 changes: 7 additions & 1 deletion doc/manual/meson.build
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Expand Up @@ -154,6 +154,8 @@ if get_option('html-manual')
nix3_cli_files,
experimental_features_shortlist_md,
experimental_feature_descriptions_md,
deprecated_features_shortlist_md,
deprecated_feature_descriptions_md,
types_dir,
conf_file_md,
builtins_md,
Expand Down Expand Up @@ -393,7 +395,11 @@ nix_manpages = [
'nix.conf',
5,
conf_file_md.full_path(),
[ conf_file_md, experimental_features_shortlist_md ],
[
conf_file_md,
experimental_features_shortlist_md,
deprecated_features_shortlist_md,
],
],
[ 'nix-daemon', 8 ],
[ 'nix-profiles', 5, 'files/profiles.md' ],
Expand Down
8 changes: 8 additions & 0 deletions doc/manual/rl-next/disallow-url-literals.md
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---
synopsis: Disallow URL literals
---

- URL literals (unquoted URLs) are now disabled by default in the Nix language.
They were previously optionally disallowable via the `no-url-literals` experimental feature, which has now been removed.
Existing Nix expressions containing URL literals must be updated to use quoted strings (e.g. `"http://example.com"` instead of `http://example.com`).
However, for transitional purposes, URL literals can be re-enabled using the new `url-literals` deprecated feature (e.g. `--extra-deprecated-features url-literals`).
1 change: 1 addition & 0 deletions doc/manual/source/SUMMARY.md.in
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Expand Up @@ -150,6 +150,7 @@
- [JSON guideline](development/json-guideline.md)
- [C++ style guide](development/cxx.md)
- [Experimental Features](development/experimental-features.md)
- [Deprecated Features](development/deprecated-features.md)
- [Contributing](development/contributing.md)
- [Releases](release-notes/index.md)
{{#include ./SUMMARY-rl-next.md}}
Expand Down
20 changes: 20 additions & 0 deletions doc/manual/source/command-ref/meson.build
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Expand Up @@ -18,6 +18,26 @@ experimental_features_shortlist_md = custom_target(
env : nix_env_for_docs,
)

dp_features_json = custom_target(
command : [ nix, '__dump-dp-features' ],
capture : true,
output : 'dp-features.json',
env : nix_env_for_docs,
)

deprecated_features_shortlist_md = custom_target(
command : nix_eval_for_docs + [
'--expr', 'import @INPUT0@ (builtins.fromJSON (builtins.readFile ./@INPUT1@))',
],
input : [
'../../generate-dp-features-shortlist.nix',
dp_features_json,
],
output : 'deprecated-features-shortlist.md',
capture : true,
env : nix_env_for_docs,
)

nix3_cli_files = custom_target(
command : [ python.full_path(), '@INPUT0@', '@OUTPUT@', '--' ] + nix_eval_for_docs + [
'--expr', 'import @INPUT1@ true (builtins.readFile ./@INPUT2@)',
Expand Down
11 changes: 11 additions & 0 deletions doc/manual/source/development/deprecated-features.md
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This section describes the notion of *deprecated features*, and how it fits into the big picture of the development of Nix.

# What are deprecated features?

Deprecated features are legacy features that are scheduled for removal.
They are disabled by default but can be re-enabled by toggling the associated [deprecated feature flags](@docroot@/command-ref/conf-file.md#conf-deprecated-features).
This allows for a transition period where users can adapt their code.

# Deprecated feature descriptions

{{#include @generated@/development/deprecated-feature-descriptions.md}}
13 changes: 13 additions & 0 deletions doc/manual/source/development/meson.build
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Expand Up @@ -10,3 +10,16 @@ experimental_feature_descriptions_md = custom_target(
env : nix_env_for_docs,
output : 'experimental-feature-descriptions.md',
)

deprecated_feature_descriptions_md = custom_target(
command : nix_eval_for_docs + [
'--expr', 'import @INPUT0@ (builtins.fromJSON (builtins.readFile @INPUT1@))',
],
input : [
'../../generate-dp-features.nix',
dp_features_json,
],
capture : true,
env : nix_env_for_docs,
output : 'deprecated-feature-descriptions.md',
)
5 changes: 3 additions & 2 deletions src/libexpr/parser.y
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Expand Up @@ -26,6 +26,7 @@
#include "nix/util/finally.hh"
#include "nix/util/util.hh"
#include "nix/util/users.hh"
#include "nix/util/configuration.hh"

#include "nix/expr/nixexpr.hh"
#include "nix/expr/eval.hh"
Expand Down Expand Up @@ -314,12 +315,12 @@ expr_simple
state->exprs.add<ExprString>(state->exprs.alloc, path)});
}
| URI {
static bool noURLLiterals = experimentalFeatureSettings.isEnabled(Xp::NoUrlLiterals);
if (noURLLiterals)
if (!experimentalFeatureSettings.isEnabled(DeprecatedFeature::UrlLiterals)) {
throw ParseError({
.msg = HintFmt("URL literals are disabled"),
.pos = state->positions[CUR_POS]
});
}
$$ = state->exprs.add<ExprString>(state->exprs.alloc, $1);
}
| '(' expr ')' { $$ = $2; }
Expand Down
2 changes: 1 addition & 1 deletion src/libutil/config-global.cc
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Expand Up @@ -64,7 +64,7 @@ GlobalConfig::Register::Register(Config * config)
configRegistrations().emplace_back(config);
}

ExperimentalFeatureSettings experimentalFeatureSettings;
FeatureSettings experimentalFeatureSettings;

static GlobalConfig::Register rSettings(&experimentalFeatureSettings);

Expand Down
63 changes: 59 additions & 4 deletions src/libutil/configuration.cc
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Expand Up @@ -3,6 +3,7 @@
#include "nix/util/abstract-setting-to-json.hh"
#include "nix/util/environment-variables.hh"
#include "nix/util/experimental-features.hh"
#include "nix/util/deprecated-features.hh"
#include "nix/util/util.hh"
#include "nix/util/file-system.hh"

Expand Down Expand Up @@ -425,6 +426,36 @@ std::string BaseSetting<std::set<ExperimentalFeature>>::to_string() const
return concatStringsSep(" ", stringifiedXpFeatures);
}

template<>
std::set<DeprecatedFeature> BaseSetting<std::set<DeprecatedFeature>>::parse(const std::string & str) const
{
std::set<DeprecatedFeature> res;
for (auto & s : tokenizeString<StringSet>(str)) {
if (auto thisDpFeature = parseDeprecatedFeature(s); thisDpFeature)
res.insert(thisDpFeature.value());
else
warn("unknown deprecated feature '%s'", s);
}
return res;
}

template<>
void BaseSetting<std::set<DeprecatedFeature>>::appendOrSet(std::set<DeprecatedFeature> newValue, bool append)
{
if (!append)
value.clear();
value.insert(std::make_move_iterator(newValue.begin()), std::make_move_iterator(newValue.end()));
}

template<>
std::string BaseSetting<std::set<DeprecatedFeature>>::to_string() const
{
StringSet stringifiedDpFeatures;
for (const auto & feature : value)
stringifiedDpFeatures.insert(std::string(showDeprecatedFeature(feature)));
return concatStringsSep(" ", stringifiedDpFeatures);
}

template<>
StringMap BaseSetting<StringMap>::parse(const std::string & str) const
{
Expand Down Expand Up @@ -505,6 +536,7 @@ template class BaseSetting<Strings>;
template class BaseSetting<StringSet>;
template class BaseSetting<StringMap>;
template class BaseSetting<std::set<ExperimentalFeature>>;
template class BaseSetting<std::set<DeprecatedFeature>>;
template class BaseSetting<std::filesystem::path>;
template class BaseSetting<std::optional<std::filesystem::path>>;

Expand Down Expand Up @@ -548,24 +580,47 @@ void OptionalPathSetting::operator=(const std::optional<Path> & v)
this->assign(v);
}

bool ExperimentalFeatureSettings::isEnabled(const ExperimentalFeature & feature) const
bool FeatureSettings::isEnabled(const ExperimentalFeature & feature) const
{
auto & f = experimentalFeatures.get();
return std::find(f.begin(), f.end(), feature) != f.end();
}

void ExperimentalFeatureSettings::require(const ExperimentalFeature & feature, std::string reason) const
void FeatureSettings::require(const ExperimentalFeature & feature, std::string reason) const
{
if (!isEnabled(feature))
throw MissingExperimentalFeature(feature, std::move(reason));
}

bool ExperimentalFeatureSettings::isEnabled(const std::optional<ExperimentalFeature> & feature) const
bool FeatureSettings::isEnabled(const std::optional<ExperimentalFeature> & feature) const
{
return !feature || isEnabled(*feature);
}

void FeatureSettings::require(const std::optional<ExperimentalFeature> & feature) const
{
if (feature)
require(*feature);
}

bool FeatureSettings::isEnabled(const DeprecatedFeature & feature) const
{
auto & f = deprecatedFeatures.get();
return std::find(f.begin(), f.end(), feature) != f.end();
}

void FeatureSettings::require(const DeprecatedFeature & feature) const
{
if (!isEnabled(feature))
throw MissingDeprecatedFeature(feature);
}

bool FeatureSettings::isEnabled(const std::optional<DeprecatedFeature> & feature) const
{
return !feature || isEnabled(*feature);
}

void ExperimentalFeatureSettings::require(const std::optional<ExperimentalFeature> & feature) const
void FeatureSettings::require(const std::optional<DeprecatedFeature> & feature) const
{
if (feature)
require(*feature);
Expand Down
100 changes: 100 additions & 0 deletions src/libutil/deprecated-features.cc
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#include "nix/util/deprecated-features.hh"
#include "nix/util/fmt.hh"
#include "nix/util/strings.hh"
#include "nix/util/util.hh"

#include <nlohmann/json.hpp>

namespace nix {

struct DeprecatedFeatureDetails
{
DeprecatedFeature tag;
std::string_view name;
std::string_view description;
};

// Add features here
constexpr std::array<DeprecatedFeatureDetails, 1> depFeatureDetails = {{{
.tag = DeprecatedFeature::UrlLiterals,
.name = "url-literals",
.description = R"(
Re-enable support for URL literals.
)",
}}};

const std::optional<DeprecatedFeature> parseDeprecatedFeature(const std::string_view & name)
{
using ReverseDepMap = std::map<std::string_view, DeprecatedFeature>;

static std::unique_ptr<ReverseDepMap> reverseDepMap = []() {
auto reverseDepMap = std::make_unique<ReverseDepMap>();
for (auto & depFeature : depFeatureDetails)
(*reverseDepMap)[depFeature.name] = depFeature.tag;
return reverseDepMap;
}();

if (auto feature = get(*reverseDepMap, name))
return *feature;
else
return std::nullopt;
}

std::string_view showDeprecatedFeature(const DeprecatedFeature tag)
{
for (const auto & detail : depFeatureDetails) {
if (detail.tag == tag)
return detail.name;
}
throw Error("Unknown deprecated feature tag");
}

nlohmann::json documentDeprecatedFeatures()
{
std::map<std::string, std::string> res;
for (auto & depFeature : depFeatureDetails)
res[std::string{depFeature.name}] = trim(stripIndentation(depFeature.description));
return (nlohmann::json) res;
}

std::set<DeprecatedFeature> parseDeprecatedFeatures(const std::set<std::string> & rawFeatures)
{
std::set<DeprecatedFeature> res;
for (auto & rawFeature : rawFeatures)
if (auto feature = parseDeprecatedFeature(rawFeature))
res.insert(*feature);
else
warn("unknown deprecated feature '%s'", rawFeature);
return res;
}

MissingDeprecatedFeature::MissingDeprecatedFeature(DeprecatedFeature feature)
: Error(
"Feature '%1%' is deprecated and should not be used anymore; use '--extra-deprecated-features %1%' to disable this error",
showDeprecatedFeature(feature))
, missingFeature(feature)
{
}

std::ostream & operator<<(std::ostream & str, const DeprecatedFeature & feature)
{
return str << showDeprecatedFeature(feature);
}

void to_json(nlohmann::json & j, const DeprecatedFeature & feature)
{
j = showDeprecatedFeature(feature);
}

void from_json(const nlohmann::json & j, DeprecatedFeature & feature)
{
const std::string input = j;
const auto parsed = parseDeprecatedFeature(input);

if (parsed.has_value())
feature = *parsed;
else
throw Error("Unknown deprecated feature '%s' in JSON input", input);
}

} // namespace nix
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