please_go: remove Go <= 1.19 coverage generation code (#291)

Go 1.20 made breaking changes to the way in which coverage is computed.
This required the `coverageredesign` GOEXPERIMENT to be enabled when
using go-rules with Go 1.20 onwards.

Go 1.19 has now been EOL for almost a year, and the `coveragedesign`
GOEXPERIMENT will be removed from Go shortly, having been the default
for around 18 months. Remove the following features from please_go that
supported the Go <= 1.19 method of computing coverage:

* The `covervars` command, which is no longer necessary with
  `coverageredesign`.
* The generation of Go <= 1.19-compatible test main files with the
  `testmain` command.

tools/please_go/BUILD

@@ -10,7 +10,6 @@ go_binary(
     deps = [
         "//third_party/go:flags",
         "//tools/please_go/cover",
-        "//tools/please_go/covervars",
         "//tools/please_go/embed",
         "//tools/please_go/filter",
         "//tools/please_go/generate",
@@ -38,7 +37,6 @@ genrule(
     visibility = ["PUBLIC"],
     deps = [
         "//tools/please_go/cover:srcs",
-        "//tools/please_go/covervars:srcs",
         "//tools/please_go/embed:srcs",
         "//tools/please_go/filter:srcs",
         "//tools/please_go/generate:srcs",

tools/please_go/please_go.go

@@ -10,7 +10,6 @@ import (
 	"github.com/peterebden/go-cli-init/v5/flags"
 
 	"github.com/please-build/go-rules/tools/please_go/cover"
-	"github.com/please-build/go-rules/tools/please_go/covervars"
 	"github.com/please-build/go-rules/tools/please_go/embed"
 	"github.com/please-build/go-rules/tools/please_go/filter"
 	"github.com/please-build/go-rules/tools/please_go/generate"
@@ -52,12 +51,6 @@ var opts = struct {
 			Sources []string `positional-arg-name:"sources" description:"Test source files" required:"true"`
 		} `positional-args:"true" required:"true"`
 	} `command:"testmain" alias:"t" description:"Generates a go main package to run the tests in a package."`
-	CoverVars struct {
-		ImportPath string `short:"i" long:"import_path" description:"The import path for the source files"`
-		Args       struct {
-			Sources []string `positional-arg-name:"sources" description:"Source files to generate embed config for"`
-		} `positional-args:"true"`
-	} `command:"covervars" description:"Generates coverage variable config for a set of go src files"`
 	Cover struct {
 		GoTool      string `short:"g" long:"go" default:"go" env:"TOOLS_GO" description:"Go binary to run"`
 		CoverTool   string `short:"t" long:"go_cover" env:"TOOLS_COVER" description:"Go coverage tool to run"`
@@ -170,10 +163,6 @@ var subCommands = map[string]func() int{
 		}
 		return 0
 	},
-	"covervars": func() int {
-		covervars.GenCoverVars(os.Stdout, opts.CoverVars.ImportPath, opts.CoverVars.Args.Sources)
-		return 0
-	},
 	"filter": func() int {
 		filter.Filter(opts.Filter.Tags, opts.Filter.Args.Sources)
 		return 0

tools/please_go/test/BUILD

@@ -9,7 +9,6 @@ filegroup(
 go_library(
     name = "test",
     srcs = [
-        "find_cover_vars.go",
         "gotest.go",
         "write_test_main.go",
     ],
@@ -19,18 +18,6 @@ go_library(
     ],
 )
 
-go_test(
-    name = "find_cover_vars_test",
-    srcs = ["find_cover_vars_test.go"],
-    data = [
-        "test_data",
-    ],
-    deps = [
-        ":test",
-        "//third_party/go:testify",
-    ],
-)
-
 go_test(
     name = "write_test_main_test",
     srcs = ["write_test_main_test.go"],

tools/please_go/test/gotest.go

@@ -2,28 +2,11 @@ package test
 
 import (
 	"log"
-
-	"github.com/please-build/go-rules/tools/please_go/install/toolchain"
 )
 
 // PleaseGoTest will generate the test main for the provided sources
 func PleaseGoTest(goTool, dir, testPackage, output string, sources, exclude []string, isBenchmark, external bool) {
-	tc := toolchain.Toolchain{GoTool: goTool}
-	minor, err := tc.GoMinorVersion()
-	if err != nil {
-		log.Fatalf("Failed to determine Go version: %s", err)
-	}
-	if minor >= 20 {
-		if err := WriteTestMain(testPackage, sources, output, dir != "", nil, isBenchmark, true, true); err != nil {
-			log.Fatalf("Error writing test main: %s", err)
-		}
-		return
-	}
-	coverVars, err := FindCoverVars(dir, testPackage, external, exclude)
-	if err != nil {
-		log.Fatalf("Error scanning for coverage: %s", err)
-	}
-	if err := WriteTestMain(testPackage, sources, output, dir != "", coverVars, isBenchmark, minor >= 18, false); err != nil {
+	if err := WriteTestMain(testPackage, sources, output, dir != "", isBenchmark, true); err != nil {
 		log.Fatalf("Error writing test main: %s", err)
 	}
 }

tools/please_go/test/test_data/test/example_test.go

@@ -24,27 +24,6 @@ func TestReadCopiedPkgdef(t *testing.T) {
 	assert.Equal(t, coverageVars, vars)
 }
 
-func TestFindCoverVars(t *testing.T) {
-	vars, err := FindCoverVars("src/build/go/test_data", []string{"src/build/go/test_data/x"})
-	assert.NoError(t, err)
-	assert.Equal(t, coverageVars, vars)
-}
-
-func TestFindCoverVarsFailsGracefully(t *testing.T) {
-	_, err := FindCoverVars("wibble", []string{})
-	assert.Error(t, err)
-}
-
-func TestFindCoverVarsReturnsNothingForEmptyPath(t *testing.T) {
-	vars, err := FindCoverVars("", []string{})
-	assert.NoError(t, err)
-	assert.Equal(t, 0, len(vars))
-}
-
 func readPkgdef(name string) ([]string, error) {
 	return nil, nil
 }
-
-func FindCoverVars(filename string, vars []string) ([]string, error) {
-	return nil, nil
-}