Makefile: validate that each commit can at least build

it is very useful when using git bisect that at least the commit can
build.

got inspiration from: https://twitter.com/pid_eins/status/1072797993760423941

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

.cirrus.yml

@@ -22,6 +22,7 @@ env:
     # Save a little typing (path relative to $CIRRUS_WORKING_DIR)
     SCRIPT_BASE: "./contrib/cirrus"
     PACKER_BASE: "./contrib/cirrus/packer"
+    CIRRUS_CLONE_DEPTH: 200
 
     ####
     #### Variables for composing new cache-images (used in PR testing) from
@@ -97,11 +98,33 @@ gating_task:
         - '/usr/local/bin/entrypoint.sh lint'
 
 
+build_each_commit_task:
+
+    depends_on:
+        - "gating"
+
+    gce_instance:
+        image_project: "libpod-218412"
+        zone: "us-central1-a"  # Required by Cirrus for the time being
+        cpu: 2
+        memory: "4Gb"
+        disk: 40
+        matrix:
+            image_name: "fedora-29-libpod-0c954a67"
+
+    timeout_in: 20m
+
+    script:
+        - $SCRIPT_BASE/setup_environment.sh
+        - git fetch --depth $CIRRUS_CLONE_DEPTH origin $CIRRUS_BASE_BRANCH
+        - env GOPATH=/var/tmp/go/ make build-all-new-commits GIT_BASE_BRANCH=origin/$CIRRUS_BASE_BRANCH
+
 # This task does the unit and integration testing for every platform
 testing_task:
 
     depends_on:
         - "gating"
+        - "build_each_commit"
 
     gce_instance:
         image_project: "libpod-218412"

Makefile

@@ -5,6 +5,7 @@ HEAD ?= HEAD
 CHANGELOG_BASE ?= HEAD~
 CHANGELOG_TARGET ?= HEAD
 PROJECT := github.com/containers/libpod
+GIT_BASE_BRANCH ?= origin/master
 GIT_BRANCH ?= $(shell git rev-parse --abbrev-ref HEAD 2>/dev/null)
 GIT_BRANCH_CLEAN ?= $(shell echo $(GIT_BRANCH) | sed -e "s/[^[:alnum:]]/-/g")
 LIBPOD_IMAGE ?= libpod_dev$(if $(GIT_BRANCH_CLEAN),:$(GIT_BRANCH_CLEAN))
@@ -345,6 +346,10 @@ API.md: cmd/podman/varlink/io.podman.varlink
 
 validate: gofmt .gitvalidation
 
+build-all-new-commits:
+	# Validate that all the commits build on top of $(GIT_BASE_BRANCH)
+	git rebase $(GIT_BASE_BRANCH) -x make
+
 .PHONY: \
 	.gopathok \
 	binaries \