Make <nix/buildenv.nix> a builtin builder

This avoids sandbox annoyances.

3 files changed, 197 insertions, 0 deletions

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 5c548755c..082cd7db0 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -2949,6 +2949,8 @@ void DerivationGoal::runChild()
 
                 if (drv->builder == "builtin:fetchurl")
                     builtinFetchurl(drv2, netrcData);
+                else if (drv->builder == "builtin:buildenv")
+                    builtinBuildenv(drv2);
                 else
                     throw Error(format("unsupported builtin function '%1%'") % string(drv->builder, 8));
                 _exit(0);
diff --git a/src/libstore/builtins.hh b/src/libstore/builtins.hh
index 0cc6ba31f..0d2da873e 100644
--- a/src/libstore/builtins.hh
+++ b/src/libstore/builtins.hh
@@ -4,6 +4,8 @@
 
 namespace nix {
 
+// TODO: make pluggable.
 void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData);
+void builtinBuildenv(const BasicDerivation & drv);
 
 }
diff --git a/src/libstore/builtins/buildenv.cc b/src/libstore/builtins/buildenv.cc
new file mode 100644
index 000000000..938d02c35
--- /dev/null
+++ b/src/libstore/builtins/buildenv.cc
@@ -0,0 +1,193 @@
+#include "builtins.hh"
+
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <algorithm>
+
+namespace nix {
+
+typedef std::map<Path,int> Priorities;
+
+static bool isDirectory(const Path & path)
+{
+    struct stat st;
+    if (stat(path.c_str(), &st) == -1)
+        throw SysError(format("getting status of '%1%'") % path);
+    return S_ISDIR(st.st_mode);
+}
+
+// FIXME: change into local variables.
+
+static Priorities priorities;
+
+static unsigned long symlinks;
+
+/* For each activated package, create symlinks */
+static void createLinks(const Path & srcDir, const Path & dstDir, int priority)
+{
+    auto srcFiles = readDirectory(srcDir);
+    for (const auto & ent : srcFiles) {
+        if (ent.name[0] == '.')
+            /* not matched by glob */
+            continue;
+        const auto & srcFile = srcDir + "/" + ent.name;
+        auto dstFile = dstDir + "/" + ent.name;
+
+        /* The files below are special-cased to that they don't show up
+         * in user profiles, either because they are useless, or
+         * because they would cauase pointless collisions (e.g., each
+         * Python package brings its own
+         * `$out/lib/pythonX.Y/site-packages/easy-install.pth'.)
+         */
+        if (hasSuffix(srcFile, "/propagated-build-inputs") ||
+            hasSuffix(srcFile, "/nix-support") ||
+            hasSuffix(srcFile, "/perllocal.pod") ||
+            hasSuffix(srcFile, "/info/dir") ||
+            hasSuffix(srcFile, "/log")) {
+            continue;
+        } else if (isDirectory(srcFile)) {
+            struct stat dstSt;
+            auto res = lstat(dstFile.c_str(), &dstSt);
+            if (res == 0) {
+                if (S_ISDIR(dstSt.st_mode)) {
+                    createLinks(srcFile, dstFile, priority);
+                    continue;
+                } else if (S_ISLNK(dstSt.st_mode)) {
+                    auto target = readLink(dstFile);
+                    if (!isDirectory(target))
+                        throw Error(format("collision between '%1%' and non-directory '%2%'")
+                            % srcFile % target);
+                    if (unlink(dstFile.c_str()) == -1)
+                        throw SysError(format("unlinking '%1%'") % dstFile);
+                    if (mkdir(dstFile.c_str(), 0755) == -1)
+                        throw SysError(format("creating directory '%1%'"));
+                    createLinks(target, dstFile, priorities[dstFile]);
+                    createLinks(srcFile, dstFile, priority);
+                    continue;
+                }
+            } else if (errno != ENOENT)
+                throw SysError(format("getting status of '%1%'") % dstFile);
+        } else {
+            struct stat dstSt;
+            auto res = lstat(dstFile.c_str(), &dstSt);
+            if (res == 0) {
+                if (S_ISLNK(dstSt.st_mode)) {
+                    auto target = readLink(dstFile);
+                    auto prevPriority = priorities[dstFile];
+                    if (prevPriority == priority)
+                        throw Error(format(
+                                "packages '%1%' and '%2%' have the same priority %3%; "
+                                "use 'nix-env --set-flag priority NUMBER INSTALLED_PKGNAME' "
+                                "to change the priority of one of the conflicting packages"
+                                " (0 being the highest priority)"
+                                ) % srcFile % target % priority);
+                    if (prevPriority < priority)
+                        continue;
+                    if (unlink(dstFile.c_str()) == -1)
+                        throw SysError(format("unlinking '%1%'") % dstFile);
+                }
+            } else if (errno != ENOENT)
+                throw SysError(format("getting status of '%1%'") % dstFile);
+        }
+        createSymlink(srcFile, dstFile);
+        priorities[dstFile] = priority;
+        symlinks++;
+    }
+}
+
+typedef std::set<Path> FileProp;
+
+static FileProp done;
+static FileProp postponed = FileProp{};
+
+static Path out;
+
+static void addPkg(const Path & pkgDir, int priority)
+{
+    if (done.find(pkgDir) != done.end())
+        return;
+    done.insert(pkgDir);
+    createLinks(pkgDir, out, priority);
+    auto propagatedFN = pkgDir + "/nix-support/propagated-user-env-packages";
+    std::string propagated;
+    {
+        AutoCloseFD fd = open(propagatedFN.c_str(), O_RDONLY | O_CLOEXEC);
+        if (!fd) {
+            if (errno == ENOENT)
+                return;
+            throw SysError(format("opening '%1%'") % propagatedFN);
+        }
+        propagated = readFile(fd.get());
+    }
+    for (const auto & p : tokenizeString<std::vector<string>>(propagated, " \n"))
+        if (done.find(p) == done.end())
+            postponed.insert(p);
+}
+
+struct Package {
+    Path path;
+    bool active;
+    int priority;
+    Package(Path path, bool active, int priority) : path{path}, active{active}, priority{priority} {}
+};
+
+typedef std::vector<Package> Packages;
+
+void builtinBuildenv(const BasicDerivation & drv)
+{
+    auto getAttr = [&](const string & name) {
+        auto i = drv.env.find(name);
+        if (i == drv.env.end()) throw Error("attribute '%s' missing", name);
+        return i->second;
+    };
+
+    out = getAttr("out");
+    createDirs(out);
+
+    /* Convert the stuff we get from the environment back into a
+     * coherent data type. */
+    Packages pkgs;
+    auto derivations = tokenizeString<Strings>(getAttr("derivations"));
+    while (!derivations.empty()) {
+        /* !!! We're trusting the caller to structure derivations env var correctly */
+        auto active = derivations.front(); derivations.pop_front();
+        auto priority = stoi(derivations.front()); derivations.pop_front();
+        auto outputs = stoi(derivations.front()); derivations.pop_front();
+        for (auto n = 0; n < outputs; n++) {
+            auto path = derivations.front(); derivations.pop_front();
+            pkgs.emplace_back(path, active != "false", priority);
+        }
+    }
+
+    /* Symlink to the packages that have been installed explicitly by the
+     * user. Process in priority order to reduce unnecessary
+     * symlink/unlink steps.
+     */
+    std::sort(pkgs.begin(), pkgs.end(), [](const Package & a, const Package & b) {
+        return a.priority < b.priority || (a.priority == b.priority && a.path < b.path);
+    });
+    for (const auto & pkg : pkgs)
+        if (pkg.active)
+            addPkg(pkg.path, pkg.priority);
+
+    /* Symlink to the packages that have been "propagated" by packages
+     * installed by the user (i.e., package X declares that it wants Y
+     * installed as well). We do these later because they have a lower
+     * priority in case of collisions.
+     */
+    auto priorityCounter = 1000;
+    while (!postponed.empty()) {
+        auto pkgDirs = postponed;
+        postponed = FileProp{};
+        for (const auto & pkgDir : pkgDirs)
+            addPkg(pkgDir, priorityCounter++);
+    }
+
+    printError("created %d symlinks in user environment", symlinks);
+
+    createSymlink(getAttr("manifest"), out + "/manifest.nix");
+}
+
+}
+