Use StringData for Nix language value documentation too

src/libcmd/repl.cc

@@ -656,7 +656,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
                             + "\n\n";
             }
 
-            markdown += stripIndentation(doc->doc);
+            markdown += stripIndentation(doc->doc.view());
 
             logger->cout(trim(renderMarkdownToTerminal(markdown)));
         } else if (fallbackPos) {

src/libexpr-c/nix_api_value.cc

@@ -134,7 +134,7 @@ PrimOp * nix_alloc_primop(
                     .name = name,
                     .args = {},
                     .arity = (size_t) arity,
-                    .doc = doc,
+                    .doc = &nix::StringData::make(doc),
                     .fun = std::bind(nix_c_primop_wrapper, fun, user_data, _1, _2, _3, _4)};
         if (args)
             for (size_t i = 0; args[i]; i++)

src/libexpr-tests/json.cc

@@ -1,6 +1,6 @@
 #include "nix/expr/tests/libexpr.hh"
 #include "nix/expr/value-to-json.hh"
-#include "nix/expr/static-string-data.hh"
+#include "nix/expr/string-data-static.hh"
 
 namespace nix {
 // Testing the conversion to JSON

src/libexpr-tests/value/print.cc

@@ -1,5 +1,5 @@
 #include "nix/expr/tests/libexpr.hh"
-#include "nix/expr/static-string-data.hh"
+#include "nix/expr/string-data-static.hh"
 
 #include "nix/expr/value.hh"
 #include "nix/expr/print.hh"

src/libexpr-tests/value/value.cc

@@ -1,5 +1,5 @@
 #include "nix/expr/value.hh"
-#include "nix/expr/static-string-data.hh"
+#include "nix/expr/string-data-static.hh"
 
 #include "nix/store/tests/libstore.hh"
 #include <gtest/gtest.h>

src/libexpr/eval.cc

@@ -51,36 +51,6 @@ using json = nlohmann::json;
 
 namespace nix {
 
-/**
- * Just for doc strings. Not for regular string values.
- */
-static char * allocString(size_t size)
-{
-    char * t;
-    t = (char *) GC_MALLOC_ATOMIC(size);
-    if (!t)
-        throw std::bad_alloc();
-    return t;
-}
-
-// When there's no need to write to the string, we can optimize away empty
-// string allocations.
-// This function handles makeImmutableString(std::string_view()) by returning
-// the empty string.
-/**
- * Just for doc strings. Not for regular string values.
- */
-static const char * makeImmutableString(std::string_view s)
-{
-    const size_t size = s.size();
-    if (size == 0)
-        return "";
-    auto t = allocString(size + 1);
-    memcpy(t, s.data(), size);
-    t[size] = '\0';
-    return t;
-}
-
 StringData & StringData::alloc(size_t size)
 {
     void * t = GC_MALLOC_ATOMIC(sizeof(StringData) + size + 1);
@@ -571,7 +541,7 @@ std::optional<EvalState::Doc> EvalState::getDoc(Value & v)
                 .name = v2->primOp()->name,
                 .arity = v2->primOp()->arity,
                 .args = v2->primOp()->args,
-                .doc = doc,
+                .doc = *doc,
             };
     }
     if (v.isLambda()) {
@@ -613,9 +583,8 @@ std::optional<EvalState::Doc> EvalState::getDoc(Value & v)
             .name = name,
             .arity = 0, // FIXME: figure out how deep by syntax only? It's not semantically useful though...
             .args = {},
-            /* N.B. Can't use StringData here, because that would lead to an interior pointer.
-               NOTE: memory leak when compiled without GC. */
-            .doc = makeImmutableString(s.view()),
+            /* NOTE: memory leak when compiled without GC. */
+            .doc = StringData::make(s.view()),
         };
     }
     if (isFunctor(v)) {

src/libexpr/include/nix/expr/eval.hh

@@ -108,7 +108,7 @@ struct PrimOp
     /**
      * Optional free-form documentation about the primop.
      */
-    const char * doc = nullptr;
+    const StringData * doc = nullptr;
 
     /**
      * Add a trace item, while calling the `<name>` builtin.
@@ -156,7 +156,7 @@ struct Constant
     /**
      * Optional free-form documentation about the constant.
      */
-    const char * doc = nullptr;
+    const StringData * doc = nullptr;
 
     /**
      * Whether the constant is impure, and not available in pure mode.
@@ -837,11 +837,7 @@ public:
         std::optional<std::string> name;
         size_t arity;
         std::vector<std::string> args;
-        /**
-         * Unlike the other `doc` fields in this file, this one should never be
-         * `null`.
-         */
-        const char * doc;
+        const StringData & doc;
     };
 
     /**

src/libexpr/include/nix/expr/meson.build

@@ -31,7 +31,8 @@ headers = [ config_pub_h ] + files(
   'print.hh',
   'repl-exit-status.hh',
   'search-path.hh',
-  'static-string-data.hh',
+  'string-data.hh',
+  'string-data-static.hh',
   'symbol-table.hh',
   'value-to-json.hh',
   'value-to-xml.hh',

src/libexpr/include/nix/expr/nixexpr.hh

@@ -12,7 +12,7 @@
 #include "nix/expr/value.hh"
 #include "nix/expr/symbol-table.hh"
 #include "nix/expr/eval-error.hh"
-#include "nix/expr/static-string-data.hh"
+#include "nix/expr/string-data-static.hh"
 #include "nix/util/pos-idx.hh"
 #include "nix/expr/counter.hh"
 #include "nix/util/pos-table.hh"

src/libexpr/include/nix/expr/parser-state.hh

@@ -5,7 +5,7 @@
 
 #include "nix/expr/eval.hh"
 #include "nix/expr/value.hh"
-#include "nix/expr/static-string-data.hh"
+#include "nix/expr/string-data-static.hh"
 
 namespace nix {
 

src/libexpr/include/nix/expr/static-string-data.hh → src/libexpr/include/nix/expr/string-data-static.hh

@@ -1,7 +1,7 @@
 #pragma once
 ///@file
 
-#include "nix/expr/value.hh"
+#include "nix/expr/string-data.hh"
 
 namespace nix {
 

src/libexpr/include/nix/expr/string-data.hh

@@ -0,0 +1,96 @@
+#pragma once
+///@file
+
+#include <cstddef>
+#include <cstring>
+#include <memory_resource>
+#include <string_view>
+
+namespace nix {
+
+class StringData
+{
+public:
+    using size_type = std::size_t;
+
+    size_type size_;
+    char data_[];
+
+    /*
+     * This in particular ensures that we cannot have a `StringData`
+     * that we use by value, which is just what we want!
+     *
+     * Dynamically sized types aren't a thing in C++ and even flexible array
+     * members are a language extension and beyond the realm of standard C++.
+     * Technically, sizeof data_ member is 0 and the intended way to use flexible
+     * array members is to allocate sizeof(StrindData) + count * sizeof(char) bytes
+     * and the compiler will consider alignment restrictions for the FAM.
+     *
+     */
+
+    StringData(StringData &&) = delete;
+    StringData & operator=(StringData &&) = delete;
+    StringData(const StringData &) = delete;
+    StringData & operator=(const StringData &) = delete;
+    ~StringData() = default;
+
+private:
+    StringData() = delete;
+
+    explicit StringData(size_type size)
+        : size_(size)
+    {
+    }
+
+public:
+    /**
+     * Allocate StringData on the (possibly) GC-managed heap and copy
+     * the contents of s to it.
+     */
+    static const StringData & make(std::string_view s);
+
+    /**
+     * Allocate StringData on the (possibly) GC-managed heap.
+     * @param size Length of the string (without the NUL terminator).
+     */
+    static StringData & alloc(size_t size);
+
+    size_t size() const
+    {
+        return size_;
+    }
+
+    char * data() noexcept
+    {
+        return data_;
+    }
+
+    const char * data() const noexcept
+    {
+        return data_;
+    }
+
+    const char * c_str() const noexcept
+    {
+        return data_;
+    }
+
+    constexpr std::string_view view() const noexcept
+    {
+        return std::string_view(data_, size_);
+    }
+
+    template<size_t N>
+    struct Static;
+
+    static StringData & make(std::pmr::memory_resource & resource, std::string_view s)
+    {
+        auto & res =
+            *new (resource.allocate(sizeof(StringData) + s.size() + 1, alignof(StringData))) StringData(s.size());
+        std::memcpy(res.data_, s.data(), s.size());
+        res.data_[s.size()] = '\0';
+        return res;
+    }
+};
+
+} // namespace nix

src/libexpr/include/nix/expr/symbol-table.hh

@@ -3,7 +3,7 @@
 
 #include <memory_resource>
 #include "nix/expr/value.hh"
-#include "nix/expr/static-string-data.hh"
+#include "nix/expr/string-data-static.hh"
 #include "nix/util/chunked-vector.hh"
 #include "nix/util/error.hh"
 

src/libexpr/include/nix/expr/value.hh

@@ -3,16 +3,14 @@
 
 #include <bit>
 #include <cassert>
-#include <cstddef>
-#include <cstring>
 #include <memory>
-#include <memory_resource>
 #include <span>
 #include <string_view>
 #include <type_traits>
 #include <concepts>
 
 #include "nix/expr/eval-gc.hh"
+#include "nix/expr/string-data.hh"
 #include "nix/expr/value/context.hh"
 #include "nix/util/source-path.hh"
 #include "nix/expr/print-options.hh"
@@ -193,91 +191,6 @@ public:
     friend struct Value;
 };
 
-class StringData
-{
-public:
-    using size_type = std::size_t;
-
-    size_type size_;
-    char data_[];
-
-    /*
-     * This in particular ensures that we cannot have a `StringData`
-     * that we use by value, which is just what we want!
-     *
-     * Dynamically sized types aren't a thing in C++ and even flexible array
-     * members are a language extension and beyond the realm of standard C++.
-     * Technically, sizeof data_ member is 0 and the intended way to use flexible
-     * array members is to allocate sizeof(StrindData) + count * sizeof(char) bytes
-     * and the compiler will consider alignment restrictions for the FAM.
-     *
-     */
-
-    StringData(StringData &&) = delete;
-    StringData & operator=(StringData &&) = delete;
-    StringData(const StringData &) = delete;
-    StringData & operator=(const StringData &) = delete;
-    ~StringData() = default;
-
-private:
-    StringData() = delete;
-
-    explicit StringData(size_type size)
-        : size_(size)
-    {
-    }
-
-public:
-    /**
-     * Allocate StringData on the (possibly) GC-managed heap and copy
-     * the contents of s to it.
-     */
-    static const StringData & make(std::string_view s);
-
-    /**
-     * Allocate StringData on the (possibly) GC-managed heap.
-     * @param size Length of the string (without the NUL terminator).
-     */
-    static StringData & alloc(size_t size);
-
-    size_t size() const
-    {
-        return size_;
-    }
-
-    char * data() noexcept
-    {
-        return data_;
-    }
-
-    const char * data() const noexcept
-    {
-        return data_;
-    }
-
-    const char * c_str() const noexcept
-    {
-        return data_;
-    }
-
-    constexpr std::string_view view() const noexcept
-    {
-        return std::string_view(data_, size_);
-    }
-
-    template<size_t N>
-    struct Static;
-
-    static StringData & make(std::pmr::memory_resource & resource, std::string_view s)
-    {
-        auto & res =
-            *new (resource.allocate(sizeof(StringData) + s.size() + 1, alignof(StringData))) StringData(s.size());
-        std::memcpy(res.data_, s.data(), s.size());
-        res.data_[s.size()] = '\0';
-        return res;
-    }
-};
-
 namespace detail {
 
 /**