* Started implementing the new evaluation model.

* Lots of refactorings.
* Unit tests.

1 files changed, 297 insertions, 0 deletions

diff --git a/src/eval.cc b/src/eval.cc
new file mode 100644
index 0000000000..14577c8738
--- /dev/null
+++ b/src/eval.cc
@@ -0,0 +1,297 @@
+#include <map>
+#include <iostream>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "eval.hh"
+#include "globals.hh"
+#include "values.hh"
+#include "db.hh"
+
+
+/* A Unix environment is a mapping from strings to strings. */
+typedef map<string, string> Environment;
+
+
+/* Return true iff the given path exists. */
+bool pathExists(string path)
+{
+    int res;
+    struct stat st;
+    res = stat(path.c_str(), &st);
+    if (!res) return true;
+    if (errno != ENOENT)
+        throw SysError("getting status of " + path);
+    return false;
+}
+
+
+/* Compute a derived value by running a program. */
+static Hash computeDerived(Hash sourceHash, string targetName,
+    string platform, Hash prog, Environment env)
+{
+    string targetPath = nixValues + "/" + 
+        (string) sourceHash + "-nf";
+
+    /* Check whether the target already exists. */
+    if (pathExists(targetPath)) 
+        throw Error("derived value in " + targetPath + " already exists");
+
+    /* Find the program corresponding to the hash `prog'. */
+    string progPath = queryValuePath(prog);
+
+    /* Finalize the environment. */
+    env["out"] = targetPath;
+
+    /* Create a log file. */
+    string logFileName = 
+        nixLogDir + "/" + baseNameOf(targetPath) + ".log";
+    /* !!! auto-pclose on exit */
+    FILE * logFile = popen(("tee " + logFileName + " >&2").c_str(), "w"); /* !!! escaping */
+    if (!logFile)
+        throw SysError("unable to create log file " + logFileName);
+
+    try {
+
+        /* Fork a child to build the package. */
+        pid_t pid;
+        switch (pid = fork()) {
+            
+        case -1:
+            throw SysError("unable to fork");
+
+        case 0: 
+
+            try { /* child */
+
+#if 0
+                /* Try to use a prebuilt. */
+                string prebuiltHashS, prebuiltFile;
+                if (queryDB(nixDB, dbPrebuilts, hash, prebuiltHashS)) {
+
+                    try {
+                        prebuiltFile = getFile(parseHash(prebuiltHashS));
+                    } catch (Error e) {
+                        cerr << "cannot obtain prebuilt (ignoring): " << e.what() << endl;
+                        goto build;
+                    }
+                
+                    cerr << "substituting prebuilt " << prebuiltFile << endl;
+
+                    int res = system(("tar xfj " + prebuiltFile + " 1>&2").c_str()); // !!! escaping
+                    if (WEXITSTATUS(res) != 0)
+                        /* This is a fatal error, because path may now
+                           have clobbered. */
+                        throw Error("cannot unpack " + prebuiltFile);
+
+                    _exit(0);
+                }
+#endif
+
+            build:
+
+                /* Fill in the environment.  We don't bother freeing
+                   the strings, since we'll exec or die soon
+                   anyway. */
+                const char * env2[env.size() + 1];
+                int i = 0;
+                for (Environment::iterator it = env.begin();
+                     it != env.end(); it++, i++)
+                    env2[i] = (new string(it->first + "=" + it->second))->c_str();
+                env2[i] = 0;
+
+                /* Dup the log handle into stderr. */
+                if (dup2(fileno(logFile), STDERR_FILENO) == -1)
+                    throw Error("cannot pipe standard error into log file: " + string(strerror(errno)));
+            
+                /* Dup stderr to stdin. */
+                if (dup2(STDERR_FILENO, STDOUT_FILENO) == -1)
+                    throw Error("cannot dup stderr into stdout");
+
+                /* Make the program executable.  !!! hack. */
+                if (chmod(progPath.c_str(), 0755))
+                    throw Error("cannot make program executable");
+
+                /* Execute the program.  This should not return. */
+                execle(progPath.c_str(), baseNameOf(progPath).c_str(), 0, env2);
+
+                throw Error("unable to execute builder: " +
+                    string(strerror(errno)));
+            
+            } catch (exception & e) {
+                cerr << "build error: " << e.what() << endl;
+                _exit(1);
+            }
+
+        }
+
+        /* parent */
+
+        /* Close the logging pipe.  Note that this should not cause
+           the logger to exit until builder exits (because the latter
+           has an open file handle to the former). */
+        pclose(logFile);
+    
+        /* Wait for the child to finish. */
+        int status;
+        if (waitpid(pid, &status, 0) != pid)
+            throw Error("unable to wait for child");
+    
+        if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
+            throw Error("unable to build package");
+
+        /* Check whether the result was created. */
+        if (!pathExists(targetPath))
+            throw Error("program " + progPath + 
+                " failed to create a result in " + targetPath);
+
+        /* Remove write permission from the value. */
+        int res = system(("chmod -R -w " + targetPath).c_str()); // !!! escaping
+        if (WEXITSTATUS(res) != 0)
+            throw Error("cannot remove write permission from " + targetPath);
+
+    } catch (exception &) {
+//         system(("rm -rf " + targetPath).c_str());
+        throw;
+    }
+
+    /* Hash the result. */
+    Hash targetHash = hashFile(targetPath);
+
+    /* Register targetHash -> targetPath.  !!! this should be in
+       values.cc. */
+    setDB(nixDB, dbNFs, sourceHash, targetName);
+
+    /* Register that targetHash was produced by evaluating
+       sourceHash; i.e., that targetHash is a normal form of
+       sourceHash. !!! this shouldn't be here */
+    setDB(nixDB, dbNFs, sourceHash, targetHash);
+
+    return targetHash;
+}
+
+
+/* Throw an exception if the given platform string is not supported by
+   the platform we are executing on. */
+static void checkPlatform(string platform)
+{
+    if (platform != thisSystem)
+        throw Error("a `" + platform +
+            "' is required, but I am a `" + thisSystem + "'");
+}
+
+
+/* Throw an exception with an error message containing the given
+   aterm. */
+static Error badTerm(const string & msg, Expr e)
+{
+    char * s = ATwriteToString(e);
+    return Error(msg + ", in `" + s + "'");
+}
+
+
+/* Hash an expression.  Hopefully the representation used by
+   ATwriteToString() won't change, otherwise all hashes will
+   change. */
+static Hash hashExpr(Expr e)
+{
+    char * s = ATwriteToString(e);
+    debug(s);
+    return hashString(s);
+}
+
+
+/* Evaluate an expression; the result must be a string. */
+static string evalString(Expr e)
+{
+    e = evalValue(e).e;
+    char * s;
+    if (ATmatch(e, "Str(<str>)", &s)) return s;
+    else throw badTerm("string value expected", e);
+}
+
+
+/* Evaluate an expression; the result must be a external
+   non-expression reference. */
+static Hash evalExternal(Expr e)
+{
+    EvalResult r = evalValue(e);
+    char * s;
+    if (ATmatch(r.e, "External(<str>)", &s)) return r.h;
+    else throw badTerm("external non-expression value expected", r.e);
+}
+
+
+/* Evaluate an expression. */
+EvalResult evalValue(Expr e)
+{
+    EvalResult r;
+    char * s;
+    Expr eBuildPlatform, eProg;
+    ATermList args;
+
+    /* Normal forms. */
+    if (ATmatch(e, "Str(<str>)", &s) ||
+        ATmatch(e, "Bool(True)") || 
+        ATmatch(e, "Bool(False)"))
+    {
+        r.e = e;
+    }
+
+    /* External expressions. */
+
+    /* External non-expressions. */
+    else if (ATmatch(e, "External(<str>)", &s)) {
+        r.e = e;
+        r.h = parseHash(s);
+    }
+
+    /* Execution primitive. */
+
+    else if (ATmatch(e, "Exec(<term>, <term>, [<list>])",
+                 &eBuildPlatform, &eProg, &args))
+    {
+        string buildPlatform = evalString(eBuildPlatform);
+
+        checkPlatform(buildPlatform);
+
+        Hash prog = evalExternal(eProg);
+
+        Environment env;
+        while (!ATisEmpty(args)) {
+            debug("arg");
+            Expr arg = ATgetFirst(args);
+            throw badTerm("foo", arg);
+            args = ATgetNext(args);
+        }
+
+        Hash sourceHash = hashExpr(
+            ATmake("Exec(Str(<str>), External(<str>), [])",
+                buildPlatform.c_str(), ((string) prog).c_str()));
+
+        /* Do we know a normal form for sourceHash? */
+        Hash targetHash;
+        string targetHashS;
+        if (queryDB(nixDB, dbNFs, sourceHash, targetHashS)) {
+            /* Yes. */
+            targetHash = parseHash(targetHashS);
+            debug("already built: " + (string) sourceHash 
+                + " -> " + (string) targetHash);
+        } else {
+            /* No, so we compute one. */
+            targetHash = computeDerived(sourceHash, 
+                (string) sourceHash + "-nf", buildPlatform, prog, env);
+        }
+
+        r.e = ATmake("External(<str>)", ((string) targetHash).c_str());
+        r.h = targetHash;
+    }
+
+    /* Barf. */
+    else throw badTerm("invalid expression", e);
+
+    return r;
+}