Replace format-version with min-version

  * "min-version" is specified as a <major>.<minor> point version
    and uses the installed BuildStream version instead of having
    a separate versioning number for the format.

  * The presence of "format-version" is now used to indicate
    that we might be loading a BuildStream 1 project.

  * For now, where parsing the version at startup is concerned, and
    also where `bst init` is concerned, we artificially bump the
    detected BuildStream version to 2.0 if we detect a version < 2.0,
    these exceptions can be removed once 2.0 is tagged and released.

Summary of changes:

  _project.py: Now parse "min-version" and detect "format-version" to
               warn about loading a BuildStream 1 project

  _versions.py: Remove obsolete BST_FORMAT_VERSION numbers from here

  data/projectconfig.yaml: Remove old "format-version" from defaults

  utils.py: Added new private _parse_version() helper function, and another
            _get_bst_api_version() to get an adjusted API version.

  frontend/app.py, frontend/cli.py: Updated `bst init` implementation

  testing (buildstream.testing): Updated testing utilities to generate
  and use projects with min-version instead of format-version.

  tests and examples: Updated to use min-version across the board.

4 files changed, 5 insertions, 4 deletions

diff --git a/src/buildstream/testing/_sourcetests/mirror.py b/src/buildstream/testing/_sourcetests/mirror.py
index de05b894c..69042747c 100644
--- a/src/buildstream/testing/_sourcetests/mirror.py
+++ b/src/buildstream/testing/_sourcetests/mirror.py
@@ -156,7 +156,7 @@ def test_mirror_from_includes(cli, tmpdir, datafiles, kind):
 
     config_project_dir = str(tmpdir.join("config"))
     os.makedirs(config_project_dir, exist_ok=True)
-    config_project = {"name": "config"}
+    config_project = {"name": "config", "min-version": "2.0"}
     _yaml.roundtrip_dump(config_project, os.path.join(config_project_dir, "project.conf"))
     extra_mirrors = {"mirrors": [{"name": "middle-earth", "aliases": {alias: [mirror_map + "/"],}}]}
     _yaml.roundtrip_dump(extra_mirrors, os.path.join(config_project_dir, "mirrors.yml"))
@@ -199,7 +199,7 @@ def test_mirror_junction_from_includes(cli, tmpdir, datafiles, kind):
 
     config_project_dir = str(tmpdir.join("config"))
     os.makedirs(config_project_dir, exist_ok=True)
-    config_project = {"name": "config"}
+    config_project = {"name": "config", "min-version": "2.0"}
     _yaml.roundtrip_dump(config_project, os.path.join(config_project_dir, "project.conf"))
     extra_mirrors = {"mirrors": [{"name": "middle-earth", "aliases": {alias: [mirror_map + "/"],}}]}
     _yaml.roundtrip_dump(extra_mirrors, os.path.join(config_project_dir, "mirrors.yml"))
diff --git a/src/buildstream/testing/_sourcetests/project/files/sub-project/project.conf b/src/buildstream/testing/_sourcetests/project/files/sub-project/project.conf
index bbb8414a3..74cfd2583 100644
--- a/src/buildstream/testing/_sourcetests/project/files/sub-project/project.conf
+++ b/src/buildstream/testing/_sourcetests/project/files/sub-project/project.conf
@@ -1,4 +1,4 @@
 # Project config for frontend build test
 name: subtest
-
+min-version: 2.0
 element-path: elements
diff --git a/src/buildstream/testing/_sourcetests/project/project.conf b/src/buildstream/testing/_sourcetests/project/project.conf
index 05b68bfeb..22fe9477f 100644
--- a/src/buildstream/testing/_sourcetests/project/project.conf
+++ b/src/buildstream/testing/_sourcetests/project/project.conf
@@ -1,5 +1,6 @@
 # Project config for frontend build test
 name: test
+min-version: 2.0
 element-path: elements
 aliases:
   alpine: https://bst-integration-test-images.ams3.cdn.digitaloceanspaces.com/
diff --git a/src/buildstream/testing/_sourcetests/track_cross_junction.py b/src/buildstream/testing/_sourcetests/track_cross_junction.py
index 2477b37ee..2c4141936 100644
--- a/src/buildstream/testing/_sourcetests/track_cross_junction.py
+++ b/src/buildstream/testing/_sourcetests/track_cross_junction.py
@@ -68,7 +68,7 @@ def generate_project(tmpdir, name, kind, config=None):
     subproject_path = os.path.join(str(tmpdir.join(project_name)))
     os.makedirs(os.path.join(subproject_path, "elements"))
 
-    project_conf = {"name": name, "element-path": "elements"}
+    project_conf = {"name": name, "min-version": "2.0", "element-path": "elements"}
     project_conf.update(config)
     _yaml.roundtrip_dump(project_conf, os.path.join(subproject_path, "project.conf"))
     add_plugins_conf(subproject_path, kind)