From 90ba96a3d610566124529516d71f84f2a8c26ec0 Mon Sep 17 00:00:00 2001
From: Taeer Bar-Yam <taeer@bar-yam.me>
Date: Mon, 10 Nov 2025 21:33:20 +0100
Subject: [PATCH] libexpr: use std::span rather than const std::vector &

---
 src/libexpr/include/nix/expr/nixexpr.hh      | 34 +++++++++++++++++---
 src/libexpr/include/nix/expr/parser-state.hh |  7 ++--
 2 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/src/libexpr/include/nix/expr/nixexpr.hh b/src/libexpr/include/nix/expr/nixexpr.hh
index 3bf92cc12..673c14cb3 100644
--- a/src/libexpr/include/nix/expr/nixexpr.hh
+++ b/src/libexpr/include/nix/expr/nixexpr.hh
@@ -289,7 +289,7 @@ struct ExprSelect : Expr
         std::pmr::polymorphic_allocator<char> & alloc,
         const PosIdx & pos,
         Expr * e,
-        const std::span<const AttrName> & attrPath,
+        std::span<const AttrName> attrPath,
         Expr * def)
         : pos(pos)
         , nAttrPath(attrPath.size())
@@ -339,7 +339,7 @@ struct ExprOpHasAttr : Expr
     Expr * e;
     std::span<AttrName> attrPath;
 
-    ExprOpHasAttr(std::pmr::polymorphic_allocator<char> & alloc, Expr * e, const std::vector<AttrName> & attrPath)
+    ExprOpHasAttr(std::pmr::polymorphic_allocator<char> & alloc, Expr * e, std::span<AttrName> attrPath)
         : e(e)
         , attrPath({alloc.allocate_object<AttrName>(attrPath.size()), attrPath.size()})
     {
@@ -433,7 +433,7 @@ struct ExprList : Expr
 {
     std::span<Expr *> elems;
 
-    ExprList(std::pmr::polymorphic_allocator<char> & alloc, const std::vector<Expr *> & exprs)
+    ExprList(std::pmr::polymorphic_allocator<char> & alloc, std::span<Expr *> exprs)
         : elems({alloc.allocate_object<Expr *>(exprs.size()), exprs.size()})
     {
         std::ranges::copy(exprs, elems.begin());
@@ -753,7 +753,19 @@ struct ExprConcatStrings : Expr
         std::pmr::polymorphic_allocator<char> & alloc,
         const PosIdx & pos,
         bool forceString,
-        const std::vector<std::pair<PosIdx, Expr *>> & es)
+        std::span<std::pair<PosIdx, Expr *>> es)
+        : pos(pos)
+        , forceString(forceString)
+        , es({alloc.allocate_object<std::pair<PosIdx, Expr *>>(es.size()), es.size()})
+    {
+        std::ranges::copy(es, this->es.begin());
+    };
+
+    ExprConcatStrings(
+        std::pmr::polymorphic_allocator<char> & alloc,
+        const PosIdx & pos,
+        bool forceString,
+        std::initializer_list<std::pair<PosIdx, Expr *>> es)
         : pos(pos)
         , forceString(forceString)
         , es({alloc.allocate_object<std::pair<PosIdx, Expr *>>(es.size()), es.size()})
@@ -833,7 +845,19 @@ public:
     add(std::pmr::polymorphic_allocator<char> & alloc,
         const PosIdx & pos,
         bool forceString,
-        const std::vector<std::pair<PosIdx, Expr *>> & es)
+        std::span<std::pair<PosIdx, Expr *>> es)
+        requires(std::same_as<C, ExprConcatStrings>)
+    {
+        return alloc.new_object<C>(alloc, pos, forceString, es);
+    }
+
+    template<class C>
+    [[gnu::always_inline]]
+    C *
+    add(std::pmr::polymorphic_allocator<char> & alloc,
+        const PosIdx & pos,
+        bool forceString,
+        std::initializer_list<std::pair<PosIdx, Expr *>> es)
         requires(std::same_as<C, ExprConcatStrings>)
     {
         return alloc.new_object<C>(alloc, pos, forceString, es);
diff --git a/src/libexpr/include/nix/expr/parser-state.hh b/src/libexpr/include/nix/expr/parser-state.hh
index 0020d001e..9e1d17b53 100644
--- a/src/libexpr/include/nix/expr/parser-state.hh
+++ b/src/libexpr/include/nix/expr/parser-state.hh
@@ -96,8 +96,7 @@ struct ParserState
         ExprAttrs * attrs, AttrPath && attrPath, const ParserLocation & loc, Expr * e, const ParserLocation & exprLoc);
     void addAttr(ExprAttrs * attrs, AttrPath & attrPath, const Symbol & symbol, ExprAttrs::AttrDef && def);
     void validateFormals(FormalsBuilder & formals, PosIdx pos = noPos, Symbol arg = {});
-    Expr *
-    stripIndentation(const PosIdx pos, const std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>> & es);
+    Expr * stripIndentation(const PosIdx pos, std::span<std::pair<PosIdx, std::variant<Expr *, StringToken>>> es);
     PosIdx at(const ParserLocation & loc);
 };
 
@@ -239,8 +238,8 @@ inline void ParserState::validateFormals(FormalsBuilder & formals, PosIdx pos, S
             {.msg = HintFmt("duplicate formal function argument '%1%'", symbols[arg]), .pos = positions[pos]});
 }
 
-inline Expr * ParserState::stripIndentation(
-    const PosIdx pos, const std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>> & es)
+inline Expr *
+ParserState::stripIndentation(const PosIdx pos, std::span<std::pair<PosIdx, std::variant<Expr *, StringToken>>> es)
 {
     if (es.empty())
         return exprs.add<ExprString>(""_sds);