* Add an command `nix-store --query-failed-paths' to list the cached

failed paths (when using the `build-cache-failure' option).

src/libstore/local-store.cc

@@ -327,6 +327,8 @@ void LocalStore::openDB(bool create)
         "insert into FailedPaths (path, time) values (?, ?);");
     stmtHasPathFailed.create(db,
         "select time from FailedPaths where path = ?;");
+    stmtQueryFailedPaths.create(db,
+        "select path from FailedPaths;");
     stmtAddDerivationOutput.create(db,
         "insert or replace into DerivationOutputs (drv, id, path) values (?, ?, ?);");
     stmtQueryValidDerivers.create(db,
@@ -508,6 +510,25 @@ bool LocalStore::hasPathFailed(const Path & path)
 }
 
 
+PathSet LocalStore::queryFailedPaths()
+{
+    SQLiteStmtUse use(stmtQueryFailedPaths);
+
+    PathSet res;
+    int r;
+    while ((r = sqlite3_step(stmtQueryFailedPaths)) == SQLITE_ROW) {
+        const char * s = (const char *) sqlite3_column_text(stmtQueryFailedPaths, 0);
+        assert(s);
+        res.insert(s);
+    }
+
+    if (r != SQLITE_DONE)
+        throw SQLiteError(db, "error querying failed paths");
+
+    return res;
+}
+
+
 Hash parseHashField(const Path & path, const string & s)
 {
     string::size_type colon = s.find(':');

src/libstore/local-store.hh

@@ -184,6 +184,9 @@ public:
     /* Query whether `path' previously failed to build. */
     bool hasPathFailed(const Path & path);
 
+    /* Return the set of paths that have failed to build.*/
+    PathSet queryFailedPaths();
+
 private:
 
     Path schemaPath;
@@ -203,6 +206,7 @@ private:
     SQLiteStmt stmtInvalidatePath;
     SQLiteStmt stmtRegisterFailedPath;
     SQLiteStmt stmtHasPathFailed;
+    SQLiteStmt stmtQueryFailedPaths;
     SQLiteStmt stmtAddDerivationOutput;
     SQLiteStmt stmtQueryValidDerivers;
     SQLiteStmt stmtQueryDerivationOutputs;

src/nix-store/nix-store.cc

@@ -33,7 +33,7 @@ static bool indirectRoot = false;
 LocalStore & ensureLocalStore()
 {
     LocalStore * store2(dynamic_cast<LocalStore *>(store.get()));
-    if (!store2) throw Error("you don't have sufficient rights to use --verify");
+    if (!store2) throw Error("you don't have sufficient rights to use this command");
     return *store2;
 }
 
@@ -651,8 +651,7 @@ static void opOptimise(Strings opFlags, Strings opArgs)
 
     bool dryRun = false;
 
-    for (Strings::iterator i = opFlags.begin();
-         i != opFlags.end(); ++i)
+    foreach (Strings::iterator, i, opFlags)
         if (*i == "--dry-run") dryRun = true;
         else throw UsageError(format("unknown flag `%1%'") % *i);
 
@@ -667,6 +666,16 @@ static void opOptimise(Strings opFlags, Strings opArgs)
 }
 
 
+static  void opQueryFailedPaths(Strings opFlags, Strings opArgs)
+{
+    if (!opArgs.empty() || !opFlags.empty())
+        throw UsageError("no arguments expected");
+    PathSet failed = ensureLocalStore().queryFailedPaths();
+    foreach (PathSet::iterator, i, failed)
+        cout << format("%1%\n") % *i;
+}
+
+
 /* Scan the arguments; find the operation, set global flags, put all
    other flags in a list, and put all other arguments in another
    list. */
@@ -718,6 +727,8 @@ void run(Strings args)
             op = opVerify;
         else if (arg == "--optimise")
             op = opOptimise;
+        else if (arg == "--query-failed-paths")
+            op = opQueryFailedPaths;
         else if (arg == "--add-root") {
             if (i == args.end())
                 throw UsageError("`--add-root requires an argument");