From ba3cb4a04949e043669299da5497bea27b944598 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Th=C3=A9ophane=20Hufschmitt?=
 <theophane.hufschmitt@tweag.io>
Date: Fri, 18 Nov 2022 13:02:06 +0100
Subject: [PATCH] Remove all the occurences of VLAs

There's generally no strict reason for using them, and they are somewhat
fishy, so let's avoid them.
---
 src/libexpr/eval.cc         | 13 ++++++++-----
 src/libstore/derivations.cc |  9 ++++-----
 src/libstore/gc.cc          |  9 ++-------
 3 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index dfe81cbf7..d853b104b 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -41,6 +41,7 @@
 #include <boost/coroutine2/coroutine.hpp>
 #include <boost/coroutine2/protected_fixedsize_stack.hpp>
 #include <boost/context/stack_context.hpp>
+#include <boost/container/small_vector.hpp>
 
 #endif
 
@@ -1691,7 +1692,8 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                 /* We have all the arguments, so call the primop with
                    the previous and new arguments. */
 
-                Value * vArgs[arity];
+                assert(arity < 64);
+                Value * vArgs[64];
                 auto n = argsDone;
                 for (Value * arg = &vCur; arg->isPrimOpApp(); arg = arg->primOpApp.left)
                     vArgs[--n] = arg->primOpApp.right;
@@ -1748,11 +1750,12 @@ void ExprCall::eval(EvalState & state, Env & env, Value & v)
     Value vFun;
     fun->eval(state, env, vFun);
 
-    Value * vArgs[args.size()];
+
+    boost::container::small_vector<Value *, 64> vArgs(args.size());
     for (size_t i = 0; i < args.size(); ++i)
         vArgs[i] = args[i]->maybeThunk(state, env);
 
-    state.callFunction(vFun, args.size(), vArgs, v, pos);
+    state.callFunction(vFun, args.size(), vArgs.data(), v, pos);
 }
 
 
@@ -1991,8 +1994,8 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
         return result;
     };
 
-    Value values[es->size()];
-    Value * vTmpP = values;
+    boost::container::small_vector<Value, 64> values(es->size());
+    Value * vTmpP = values.data();
 
     for (auto & [i_pos, i] : *es) {
         Value & vTmp = *vTmpP++;
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 1fecd1c97..6d9c8b9d6 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -151,11 +151,10 @@ StorePath writeDerivation(Store & store,
 /* Read string `s' from stream `str'. */
 static void expect(std::istream & str, std::string_view s)
 {
-    char s2[s.size()];
-    str.read(s2, s.size());
-    std::string_view s2View { s2, s.size() };
-    if (s2View != s)
-        throw FormatError("expected string '%s', got '%s'", s, s2View);
+    for (auto & c : s) {
+        if (str.get() != c)
+            throw FormatError("expected string '%1%'", s);
+    }
 }
 
 
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 8d05ae4bd..ddec43fdc 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -330,9 +330,7 @@ typedef std::unordered_map<Path, std::unordered_set<std::string>> UncheckedRoots
 
 static void readProcLink(const std::string & file, UncheckedRoots & roots)
 {
-    /* 64 is the starting buffer size gnu readlink uses... */
-    auto bufsiz = ssize_t{64};
-try_again:
+    constexpr auto bufsiz = PATH_MAX;
     char buf[bufsiz];
     auto res = readlink(file.c_str(), buf, bufsiz);
     if (res == -1) {
@@ -341,10 +339,7 @@ try_again:
         throw SysError("reading symlink");
     }
     if (res == bufsiz) {
-        if (SSIZE_MAX / 2 < bufsiz)
-            throw Error("stupidly long symlink");
-        bufsiz *= 2;
-        goto try_again;
+        throw Error("stupidly long symlink");
     }
     if (res > 0 && buf[0] == '/')
         roots[std::string(static_cast<char *>(buf), res)]