Ignore variant when looking up command for platform in entrypoint

This change changes our runtime platform selection logic to allow
matching platforms that don't match the CPU variant, since some indexes
only provide the variant-less platform, and should be chosen in that
case rather than failing.

If the platform's command is found including the CPU variant, it will be
used. If not, we'll also check if there's a variant-less platform that
matches, and if so, we'll use that command.

cmd/entrypoint/main.go

@@ -19,6 +19,7 @@ package main
 import (
 	"encoding/json"
 	"flag"
+	"fmt"
 	"log"
 	"os"
 	"os/exec"
@@ -110,11 +111,10 @@ func main() {
 			log.Fatal(err)
 		}
 		plat := platforms.DefaultString()
-
-		var found bool
-		cmd, found = cmds[plat]
-		if !found {
-			log.Fatalf("could not find command for platform %q", plat)
+		var err error
+		cmd, err = selectCommandForPlatform(cmds, plat)
+		if err != nil {
+			log.Fatal(err)
 		}
 	}
 
@@ -173,3 +173,20 @@ func main() {
 		}
 	}
 }
+
+func selectCommandForPlatform(cmds map[string][]string, plat string) ([]string, error) {
+	cmd, found := cmds[plat]
+	if found {
+		return cmd, nil
+	}
+
+	// If the command wasn't found, check if there's a
+	// command defined for the same platform without a CPU
+	// variant specified.
+	platWithoutVariant := plat[:strings.LastIndex(plat, "/")]
+	cmd, found = cmds[platWithoutVariant]
+	if found {
+		return cmd, nil
+	}
+	return nil, fmt.Errorf("could not find command for platform %q", plat)
+}

cmd/entrypoint/namespaces_test.go

@@ -1,5 +1,21 @@
 // +build linux
 
+/*
+Copyright 2022 The Tekton Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
 package main
 
 import (

cmd/entrypoint/platform_test.go

@@ -0,0 +1,78 @@
+/*
+Copyright 2022 The Tekton Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestSelectCommandForPlatform(t *testing.T) {
+	for _, c := range []struct {
+		desc    string
+		m       map[string][]string
+		plat    string
+		want    []string
+		wantErr bool
+	}{{
+		desc: "platform exists",
+		m: map[string][]string{
+			"linux/amd64": []string{"my", "command"},
+			"linux/s390x": []string{"other", "one"},
+		},
+		plat: "linux/amd64",
+		want: []string{"my", "command"},
+	}, {
+		desc: "platform not found",
+		m: map[string][]string{
+			"linux/amd64": []string{"my", "command"},
+			"linux/s390x": []string{"other", "one"},
+		},
+		plat:    "linux/ppc64le",
+		wantErr: true,
+	}, {
+		desc: "platform fallback",
+		m: map[string][]string{
+			"linux/amd64": []string{"my", "command"},
+			"linux/s390x": []string{"other", "one"},
+		},
+		plat: "linux/amd64/v8",
+		want: []string{"my", "command"},
+	}, {
+		desc: "platform fallback not needed",
+		m: map[string][]string{
+			"linux/amd64":    []string{"other", "one"},
+			"linux/amd64/v8": []string{"my", "command"},
+		},
+		plat: "linux/amd64/v8",
+		want: []string{"my", "command"},
+	}} {
+		t.Run(c.desc, func(t *testing.T) {
+			got, err := selectCommandForPlatform(c.m, c.plat)
+			if err != nil {
+				if c.wantErr {
+					return
+				}
+				t.Fatalf("Unexpected error: %v", err)
+			}
+			if d := cmp.Diff(c.want, got); d != "" {
+				t.Fatalf("Diff(-want,+got):\n%s", d)
+			}
+		})
+	}
+}