Support Python projects

Summary:
A new root and variant `python` config field is provided with two new
fields below, `version` and `requirements`.

The former, `version`, should specify the Python executable to use when
executing related package installation commands and ostensibly the same
executable that will be used to run the application.

The latter, `requirements`, should specify all pip requirements files
such that a compiler that supports layered filesystems (e.g. Docker) can
output separate instructions that will invalidate cache layers for
changes to those files independently of changes to the rest of the
codebase.

Python related instructions will be generated only if either `version`
or `requirements` are given.

Fixes T186545

Test Plan: Run `go test ./...`.

Reviewers: thcipriani, hashar, demon, #release-engineering-team

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Maniphest Tasks: T186545

Differential Revision: https://phabricator.wikimedia.org/D976

1 files changed, 10 insertions, 8 deletions

diff --git a/config/common.go b/config/common.go
index fa100b8..a597a82 100644
--- a/config/common.go
+++ b/config/common.go
@@ -8,13 +8,14 @@ import (
 // and each configured variant.
 //
 type CommonConfig struct {
-	Base         string      `yaml:"base" validate:"omitempty,baseimage"` // name/path to base image
-	Apt          AptConfig   `yaml:"apt"`                                 // APT related configuration
-	Node         NodeConfig  `yaml:"node"`                                // Node related configuration
-	Lives        LivesConfig `yaml:"lives"`                               // application owner/dir configuration
-	Runs         RunsConfig  `yaml:"runs"`                                // runtime environment configuration
-	SharedVolume Flag        `yaml:"sharedvolume"`                        // define a volume for application
-	EntryPoint   []string    `yaml:"entrypoint"`                          // entry-point executable
+	Base         string       `yaml:"base" validate:"omitempty,baseimage"` // name/path to base image
+	Apt          AptConfig    `yaml:"apt"`                                 // APT related configuration
+	Node         NodeConfig   `yaml:"node"`                                // Node related configuration
+	Python       PythonConfig `yaml:"python"`                              // Python related configuration
+	Lives        LivesConfig  `yaml:"lives"`                               // application owner/dir configuration
+	Runs         RunsConfig   `yaml:"runs"`                                // runtime environment configuration
+	SharedVolume Flag         `yaml:"sharedvolume"`                        // define a volume for application
+	EntryPoint   []string     `yaml:"entrypoint"`                          // entry-point executable
 }
 
 // Merge takes another CommonConfig and merges its fields this one's.
@@ -26,6 +27,7 @@ func (cc *CommonConfig) Merge(cc2 CommonConfig) {
 
 	cc.Apt.Merge(cc2.Apt)
 	cc.Node.Merge(cc2.Node)
+	cc.Python.Merge(cc2.Python)
 	cc.Lives.Merge(cc2.Lives)
 	cc.Runs.Merge(cc2.Runs)
 	cc.SharedVolume.Merge(cc2.SharedVolume)
@@ -40,7 +42,7 @@ func (cc *CommonConfig) Merge(cc2 CommonConfig) {
 // injected.
 //
 func (cc *CommonConfig) PhaseCompileableConfig() []build.PhaseCompileable {
-	return []build.PhaseCompileable{cc.Apt, cc.Node, cc.Lives, cc.Runs}
+	return []build.PhaseCompileable{cc.Apt, cc.Node, cc.Python, cc.Lives, cc.Runs}
 }
 
 // InstructionsForPhase injects instructions into the given build phase for