dvc: introduce local build cache

This patch introduces `.dvc/cache/stages` that is used to store previous
runs and their results, which could then be reused later when we stumble
upon the same command with the same deps and outs.

Format of build cache entries is single-line json, which is readable by
humans and might also be used for lock files discussed in iterative#1871.

Related to iterative#1871
Local part of iterative#1234

dvc/output/base.py

@@ -155,6 +155,9 @@ def checksum(self):
     def checksum(self, checksum):
         self.info[self.remote.PARAM_CHECKSUM] = checksum
 
+    def get_checksum(self):
+        return self.remote.get_checksum(self.path_info)
+
     @property
     def is_dir_checksum(self):
         return self.remote.is_dir_checksum(self.checksum)
@@ -167,7 +170,7 @@ def save_info(self):
         return self.remote.save_info(self.path_info)
 
     def changed_checksum(self):
-        return self.checksum != self.remote.get_checksum(self.path_info)
+        return self.checksum != self.get_checksum()
 
     def changed_cache(self, filter_info=None):
         if not self.use_cache or not self.checksum:

dvc/repo/reproduce.py

@@ -102,7 +102,6 @@ def _reproduce_stages(
     G,
     stages,
     downstream=False,
-    ignore_build_cache=False,
     single_item=False,
     **kwargs
 ):
@@ -172,7 +171,7 @@ def _reproduce_stages(
         try:
             ret = _reproduce_stage(stage, **kwargs)
 
-            if len(ret) != 0 and ignore_build_cache:
+            if len(ret) != 0 and kwargs.get("ignore_build_cache", False):
                 # NOTE: we are walking our pipeline from the top to the
                 # bottom. If one stage is changed, it will be reproduced,
                 # which tells us that we should force reproducing all of

dvc/repo/run.py

@@ -57,6 +57,9 @@ def run(self, fname=None, no_exec=False, **kwargs):
 
     self.check_modified_graph([stage], self.pipeline_stages)
     if not no_exec:
-        stage.run(no_commit=kwargs.get("no_commit", False))
+        stage.run(
+            no_commit=kwargs.get("no_commit", False),
+            ignore_build_cache=kwargs.get("ignore_build_cache", False),
+        )
     dvcfile.dump(stage, update_dvcfile=True)
     return stage

dvc/stage/__init__.py

@@ -24,7 +24,7 @@
     MissingDep,
     MissingDataSource,
 )
-from . import params
+from . import params, cache as stage_cache
 from dvc.utils import dict_md5
 from dvc.utils import fix_env
 from dvc.utils import relpath
@@ -482,6 +482,8 @@ def save(self):
 
         self.md5 = self._compute_md5()
 
+        stage_cache.save(self)
+
     @staticmethod
     def _changed_entries(entries):
         return [
@@ -608,7 +610,9 @@ def _run(self):
             raise StageCmdFailedError(self)
 
     @rwlocked(read=["deps"], write=["outs"])
-    def run(self, dry=False, no_commit=False, force=False):
+    def run(
+        self, dry=False, no_commit=False, force=False, ignore_build_cache=False
+    ):
         if (self.cmd or self.is_import) and not self.locked and not dry:
             self.remove_outs(ignore_remove=False, force=False)
 
@@ -643,16 +647,20 @@ def run(self, dry=False, no_commit=False, force=False):
                 self.check_missing_outputs()
 
         else:
-            logger.info("Running command:\n\t{}".format(self.cmd))
             if not dry:
+                if not force and not ignore_build_cache:
+                    stage_cache.restore(self)
+
                 if (
                     not force
                     and not self.is_callback
                     and not self.always_changed
                     and self._already_cached()
                 ):
+                    logger.info("Stage is cached, skipping.")
                     self.checkout()
                 else:
+                    logger.info("Running command:\n\t{}".format(self.cmd))
                     self._run()
 
         if not dry:

dvc/stage/cache.py

@@ -0,0 +1,75 @@
+import os
+import json
+import hashlib
+
+from dvc.utils.fs import makedirs
+
+
+def _sha256(string):
+    return hashlib.sha256(string.encode()).hexdigest()
+
+
+def _get_hash(stage):
+    if not stage.cmd or not stage.deps or not stage.outs:
+        return None
+
+    string = _sha256(stage.cmd)
+    for dep in stage.deps:
+        if not dep.def_path or not dep.get_checksum():
+            return None
+
+        string += _sha256(dep.def_path)
+        string += _sha256(dep.get_checksum())
+
+    for out in stage.outs:
+        if not out.def_path or out.persist:
+            return None
+
+        string += _sha256(out.def_path)
+
+    return _sha256(string)
+
+
+def _get_cache(stage):
+    return {
+        "cmd": stage.cmd,
+        "deps": {dep.def_path: dep.get_checksum() for dep in stage.deps},
+        "outs": {out.def_path: out.get_checksum() for out in stage.outs},
+    }
+
+
+def _get_cache_path(stage):
+    sha = _get_hash(stage)
+    if not sha:
+        return None
+
+    cache_dir = os.path.join(stage.repo.cache.local.cache_dir, "stages")
+
+    return os.path.join(cache_dir, sha[:2], sha)
+
+
+def save(stage):
+    path = _get_cache_path(stage)
+    if not path or os.path.exists(path):
+        return
+
+    dpath = os.path.dirname(path)
+    makedirs(dpath, exist_ok=True)
+    with open(path, "w+") as fobj:
+        json.dump(_get_cache(stage), fobj)
+
+
+def restore(stage):
+    path = _get_cache_path(stage)
+    if not path or not os.path.exists(path):
+        return
+
+    with open(path, "r") as fobj:
+        cache = json.load(fobj)
+
+    outs = {out.def_path: out for out in stage.outs}
+    for def_path, checksum in cache["outs"].items():
+        outs[def_path].checksum = checksum
+
+    for dep in stage.deps:
+        dep.save()

tests/func/test_repro.py

@@ -1290,7 +1290,9 @@ def test(self):
             ["repro", self._get_stage_target(self.stage), "--no-commit"]
         )
         self.assertEqual(ret, 0)
-        self.assertFalse(os.path.exists(self.dvc.cache.local.cache_dir))
+        self.assertEqual(
+            os.listdir(self.dvc.cache.local.cache_dir), ["stages"]
+        )
 
 
 class TestReproAlreadyCached(TestRepro):