libexpr: drop bison-specific \0\0 input trailer

bison needed it for internal reasons, the new parser does not.

Change-Id: I91f7aa23fb151e3152eee793a4fdce423fcf98d9

lix/libexpr/eval.cc

@@ -2690,8 +2690,6 @@ Expr & EvalState::parseExprFromFile(const SourcePath & path)
 Expr & EvalState::parseExprFromFile(const SourcePath & path, std::shared_ptr<StaticEnv> & staticEnv)
 {
     auto buffer = path.readFile();
-    // readFile hopefully have left some extra space for terminators
-    buffer.append("\0\0", 2);
     return *parse(buffer.data(), buffer.size(), Pos::Origin(path), path.parent(), staticEnv);
 }
 
@@ -2703,12 +2701,8 @@ Expr & EvalState::parseExprFromString(
     const FeatureSettings & featureSettings
 )
 {
-    // NOTE this method (and parseStdin) must take care to *fully copy* their input
-    // into their respective Pos::Origin until the parser stops overwriting its input
-    // data.
-    auto s = make_ref<std::string>(s_);
-    s_.append("\0\0", 2);
-    return *parse(s_.data(), s_.size(), Pos::String{.source = s}, basePath, staticEnv, featureSettings);
+    auto s = make_ref<std::string>(std::move(s_));
+    return *parse(s->data(), s->size(), Pos::String{.source = s}, basePath, staticEnv, featureSettings);
 }
 
 
@@ -2724,15 +2718,9 @@ Expr & EvalState::parseExprFromString(
 
 Expr & EvalState::parseStdin()
 {
-    // NOTE this method (and parseExprFromString) must take care to *fully copy* their
-    // input into their respective Pos::Origin until the parser stops overwriting its
-    // input data.
     //Activity act(*logger, lvlTalkative, "parsing standard input");
-    auto buffer = drainFD(0);
-    // drainFD should have left some extra space for terminators
-    auto s = make_ref<std::string>(buffer);
-    buffer.append("\0\0", 2);
-    return *parse(buffer.data(), buffer.size(), Pos::Stdin{.source = s}, CanonPath::fromCwd(), staticBaseEnv);
+    auto s = make_ref<std::string>(drainFD(0));
+    return *parse(s->data(), s->size(), Pos::Stdin{.source = s}, CanonPath::fromCwd(), staticBaseEnv);
 }
 
 

lix/libexpr/parser/parser.cc

@@ -39,11 +39,6 @@ Expr * EvalState::parse(
         featureSettings,
     };
 
-    assert(length >= 2);
-    assert(text[length - 1] == 0);
-    assert(text[length - 2] == 0);
-    length -= 2;
-
     p::string_input<p::tracking_mode::lazy> inp{std::string_view{text, length}, "input"};
     try {
         parser::v1::ExprState x;

lix/libexpr/primops.cc

@@ -2851,9 +2851,7 @@ void EvalState::createBaseEnv()
        building baseEnv/staticBaseEnv because it uses 'builtins'. */
     char code[] =
         #include "primops/derivation.nix.gen.hh"
-        // the parser needs two NUL bytes as terminators; one of them
-        // is implied by being a C string.
-        "\0";
+        ;
     eval(*parse(code, sizeof(code), derivationInternal, {CanonPath::root}, staticBaseEnv), *vDerivation);
 }
 

lix/libutil/file-descriptor.cc

@@ -79,9 +79,7 @@ void writeFull(int fd, std::string_view s, bool allowInterrupts)
 
 std::string drainFD(int fd, bool block, const size_t reserveSize)
 {
-    // the parser needs two extra bytes to append terminating characters, other users will
-    // not care very much about the extra memory.
-    StringSink sink(reserveSize + 2);
+    StringSink sink(reserveSize);
     sink << drainFDSource(fd, block);
     return std::move(sink.s);
 }