CA derivations that depend on other CA derivations

Co-authored-by: Théophane Hufschmitt <regnat@users.noreply.github.com>

src/libstore/build.cc

@@ -984,6 +984,8 @@ private:
     void tryLocalBuild();
     void buildDone();
 
+    void resolvedFinished();
+
     /* Is the build hook willing to perform the build? */
     HookReply tryBuildHook();
 
@@ -1451,8 +1453,39 @@ void DerivationGoal::inputsRealised()
     /* Determine the full set of input paths. */
 
     /* First, the input derivations. */
-    if (useDerivation)
-        for (auto & [depDrvPath, wantedDepOutputs] : dynamic_cast<Derivation *>(drv.get())->inputDrvs) {
+    if (useDerivation) {
+        auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());
+
+        if (!fullDrv.inputDrvs.empty() && fullDrv.type() == DerivationType::CAFloating) {
+            /* We are be able to resolve this derivation based on the
+               now-known results of dependencies. If so, we become a stub goal
+               aliasing that resolved derivation goal */
+            Derivation drvResolved { fullDrv.resolve(worker.store) };
+
+            auto pathResolved = writeDerivation(worker.store, drvResolved);
+            /* Add to memotable to speed up downstream goal's queries with the
+               original derivation. */
+            drvPathResolutions.lock()->insert_or_assign(drvPath, pathResolved);
+
+            auto msg = fmt("Resolved derivation: '%s' -> '%s'",
+                worker.store.printStorePath(drvPath),
+                worker.store.printStorePath(pathResolved));
+            act = std::make_unique<Activity>(*logger, lvlInfo, actBuildWaiting, msg,
+                Logger::Fields {
+                       worker.store.printStorePath(drvPath),
+                       worker.store.printStorePath(pathResolved),
+                   });
+
+            auto resolvedGoal = worker.makeDerivationGoal(
+                pathResolved, wantedOutputs,
+                buildMode == bmRepair ? bmRepair : bmNormal);
+            addWaitee(resolvedGoal);
+
+            state = &DerivationGoal::resolvedFinished;
+            return;
+        }
+
+        for (auto & [depDrvPath, wantedDepOutputs] : fullDrv.inputDrvs) {
             /* Add the relevant output closures of the input derivation
                `i' as input paths.  Only add the closures of output paths
                that are specified as inputs. */
@@ -1472,6 +1505,7 @@ void DerivationGoal::inputsRealised()
                         worker.store.printStorePath(drvPath), j, worker.store.printStorePath(drvPath));
             }
         }
+    }
 
     /* Second, the input sources. */
     worker.store.computeFSClosure(drv->inputSrcs, inputPaths);
@@ -1893,6 +1927,9 @@ void DerivationGoal::buildDone()
     done(BuildResult::Built);
 }
 
+void DerivationGoal::resolvedFinished() {
+    done(BuildResult::Built);
+}
 
 HookReply DerivationGoal::tryBuildHook()
 {
@@ -2065,7 +2102,7 @@ void linkOrCopy(const Path & from, const Path & to)
            file (e.g. 32000 of ext3), which is quite possible after a
            'nix-store --optimise'. FIXME: actually, why don't we just
            bind-mount in this case?
-           
+
            It can also fail with EPERM in BeegFS v7 and earlier versions
            which don't allow hard-links to other directories */
         if (errno != EMLINK && errno != EPERM)
@@ -4248,10 +4285,14 @@ void DerivationGoal::registerOutputs()
     {
         ValidPathInfos infos2;
         for (auto & [outputName, newInfo] : infos) {
-            /* FIXME: we will want to track this mapping in the DB whether or
-               not we have a drv file. */
             if (useDerivation)
                 worker.store.linkDeriverToPath(drvPath, outputName, newInfo.path);
+            else {
+                /* Once a floating CA derivations reaches this point, it must
+                   already be resolved, drvPath the basic derivation path, and
+                   a file existsing at that path for sake of the DB's foreign key. */
+                assert(drv->type() != DerivationType::CAFloating);
+            }
             infos2.push_back(newInfo);
         }
         worker.store.registerValidPaths(infos2);

src/libstore/derivations.cc

@@ -672,4 +672,57 @@ std::string downstreamPlaceholder(const Store & store, const StorePath & drvPath
     return "/" + hashString(htSHA256, clearText).to_string(Base32, false);
 }
 
+
+// N.B. Outputs are left unchanged
+static void rewriteDerivation(Store & store, BasicDerivation & drv, const StringMap & rewrites) {
+
+    debug("Rewriting the derivation");
+
+    for (auto &rewrite: rewrites) {
+        debug("rewriting %s as %s", rewrite.first, rewrite.second);
+    }
+
+    drv.builder = rewriteStrings(drv.builder, rewrites);
+    for (auto & arg: drv.args) {
+        arg = rewriteStrings(arg, rewrites);
+    }
+
+    StringPairs newEnv;
+    for (auto & envVar: drv.env) {
+        auto envName = rewriteStrings(envVar.first, rewrites);
+        auto envValue = rewriteStrings(envVar.second, rewrites);
+        newEnv.emplace(envName, envValue);
+    }
+    drv.env = newEnv;
+}
+
+
+Sync<DrvPathResolutions> drvPathResolutions;
+
+BasicDerivation Derivation::resolve(Store & store) {
+    BasicDerivation resolved { *this };
+
+    // Input paths that we'll want to rewrite in the derivation
+    StringMap inputRewrites;
+
+    for (auto & input : inputDrvs) {
+        auto inputDrvOutputs = store.queryPartialDerivationOutputMap(input.first);
+        StringSet newOutputNames;
+        for (auto & outputName : input.second) {
+            auto actualPathOpt = inputDrvOutputs.at(outputName);
+            if (!actualPathOpt)
+                throw Error("input drv '%s' wasn't yet built", store.printStorePath(input.first));
+            auto actualPath = *actualPathOpt;
+            inputRewrites.emplace(
+                downstreamPlaceholder(store, input.first, outputName),
+                store.printStorePath(actualPath));
+            resolved.inputSrcs.insert(std::move(actualPath));
+        }
+    }
+
+    rewriteDerivation(store, resolved, inputRewrites);
+
+    return resolved;
+}
+
 }

src/libstore/derivations.hh

@@ -4,6 +4,7 @@
 #include "types.hh"
 #include "hash.hh"
 #include "content-address.hh"
+#include "sync.hh"
 
 #include <map>
 #include <variant>
@@ -127,6 +128,13 @@ struct Derivation : BasicDerivation
     std::string unparse(const Store & store, bool maskOutputs,
         std::map<std::string, StringSet> * actualInputs = nullptr) const;
 
+    /* Return the underlying basic derivation but with
+
+       1. input drv outputs moved to input sources.
+
+       2. placeholders replaced with realized input store paths. */
+    BasicDerivation resolve(Store & store);
+
     Derivation() = default;
     Derivation(BasicDerivation && bd) : BasicDerivation(std::move(bd)) { }
 };
@@ -187,6 +195,16 @@ typedef std::map<StorePath, DrvHashModulo> DrvHashes;
 
 extern DrvHashes drvHashes; // FIXME: global, not thread-safe
 
+/* Memoisation of `readDerivation(..).resove()`. */
+typedef std::map<
+    StorePath,
+    std::optional<StorePath>
+> DrvPathResolutions;
+
+// FIXME: global, though at least thread-safe.
+// FIXME: arguably overlaps with hashDerivationModulo memo table.
+extern Sync<DrvPathResolutions> drvPathResolutions;
+
 bool wantOutput(const string & output, const std::set<string> & wanted);
 
 struct Source;

src/libstore/local-store.cc

@@ -803,13 +803,36 @@ StorePathSet LocalStore::queryValidDerivers(const StorePath & path)
 }
 
 
-std::map<std::string, std::optional<StorePath>> LocalStore::queryPartialDerivationOutputMap(const StorePath & path)
+std::map<std::string, std::optional<StorePath>> LocalStore::queryPartialDerivationOutputMap(const StorePath & path_)
 {
+    auto path = path_;
     std::map<std::string, std::optional<StorePath>> outputs;
-    BasicDerivation drv = readDerivation(path);
+    Derivation drv = readDerivation(path);
     for (auto & [outName, _] : drv.outputs) {
         outputs.insert_or_assign(outName, std::nullopt);
     }
+    bool haveCached = false;
+    {
+        auto resolutions = drvPathResolutions.lock();
+        auto resolvedPathOptIter = resolutions->find(path);
+        if (resolvedPathOptIter != resolutions->end()) {
+            auto & [_, resolvedPathOpt] = *resolvedPathOptIter;
+            if (resolvedPathOpt)
+                path = *resolvedPathOpt;
+            haveCached = true;
+        }
+    }
+    /* can't just use else-if instead of `!haveCached` because we need to unlock
+       `drvPathResolutions` before it is locked in `Derivation::resolve`. */
+    if (!haveCached && drv.type() == DerivationType::CAFloating) {
+        /* Resolve drv and use that path instead. */
+        auto pathResolved = writeDerivation(*this, drv.resolve(*this));
+        /* Store in memo table. */
+        /* FIXME: memo logic should not be local-store specific, should have
+           wrapper-method instead. */
+        drvPathResolutions.lock()->insert_or_assign(path, pathResolved);
+        path = std::move(pathResolved);
+    }
     return retrySQLite<std::map<std::string, std::optional<StorePath>>>([&]() {
         auto state(_state.lock());
 

tests/content-addressed.nix

@@ -4,16 +4,40 @@ with import ./config.nix;
 # A simple content-addressed derivation.
 # The derivation can be arbitrarily modified by passing a different `seed`,
 # but the output will always be the same
-mkDerivation {
-  name = "simple-content-addressed";
-  buildCommand = ''
-    set -x
-    echo "Building a CA derivation"
-    echo "The seed is ${toString seed}"
-    mkdir -p $out
-    echo "Hello World" > $out/hello
-  '';
-  __contentAddressed = true;
-  outputHashMode = "recursive";
-  outputHashAlgo = "sha256";
+rec {
+  root = mkDerivation {
+    name = "simple-content-addressed";
+    buildCommand = ''
+      set -x
+      echo "Building a CA derivation"
+      echo "The seed is ${toString seed}"
+      mkdir -p $out
+      echo "Hello World" > $out/hello
+    '';
+    __contentAddressed = true;
+    outputHashMode = "recursive";
+    outputHashAlgo = "sha256";
+  };
+  dependent = mkDerivation {
+    name = "dependent";
+    buildCommand = ''
+      echo "building a dependent derivation"
+      mkdir -p $out
+      echo ${root}/hello > $out/dep
+    '';
+    __contentAddressed = true;
+    outputHashMode = "recursive";
+    outputHashAlgo = "sha256";
+  };
+  transitivelyDependent = mkDerivation {
+    name = "transitively-dependent";
+    buildCommand = ''
+      echo "building transitively-dependent"
+      cat ${dependent}/dep
+      echo ${dependent} > $out
+    '';
+    __contentAddressed = true;
+    outputHashMode = "recursive";
+    outputHashAlgo = "sha256";
+  };
 }

tests/content-addressed.sh

@@ -2,15 +2,17 @@
 
 source common.sh
 
-clearStore
-clearCache
-
-export REMOTE_STORE=file://$cacheDir
-
-drv=$(nix-instantiate --experimental-features ca-derivations ./content-addressed.nix --arg seed 1)
+drv=$(nix-instantiate --experimental-features ca-derivations ./content-addressed.nix -A root --arg seed 1)
 nix --experimental-features 'nix-command ca-derivations' show-derivation --derivation "$drv" --arg seed 1
 
-out1=$(nix-build --experimental-features ca-derivations ./content-addressed.nix --arg seed 1 --no-out-link)
-out2=$(nix-build --experimental-features ca-derivations ./content-addressed.nix --arg seed 2 --no-out-link)
+testDerivation () {
+    local derivationPath=$1
+    local commonArgs=("--experimental-features" "ca-derivations" "./content-addressed.nix" "-A" "$derivationPath" "--no-out-link")
+    local out1=$(nix-build "${commonArgs[@]}" --arg seed 1)
+    local out2=$(nix-build "${commonArgs[@]}" --arg seed 2)
+    test $out1 == $out2
+}
 
-test $out1 == $out2
+testDerivation root
+testDerivation dependent
+testDerivation transitivelyDependent