compileopts: don't filter build tags, use specific build tags instead

This basically reverts https://github.com/tinygo-org/tinygo/pull/3357
and replaces it with a different mechanism to get to the same goal.

I do not think filtering tags like this is a good idea: it's the wrong
part of the compiler to be concerned with such tags (that part sets
tags, but doesn't modify existing tags). Instead, I've written the
//go:build lines in such a way that it has the same effect: WASI
defaults to leveldb, everything else defaults to fnv, and it's possible
to override the default using build tags.

compileopts/config.go

@@ -75,8 +75,7 @@ func (c *Config) GOARM() string {
 
 // BuildTags returns the complete list of build tags used during this build.
 func (c *Config) BuildTags() []string {
-	targetTags := filterTags(c.Target.BuildTags, c.Options.Tags)
+	tags := append(c.Target.BuildTags, []string{"tinygo", "math_big_pure_go", "gc." + c.GC(), "scheduler." + c.Scheduler(), "serial." + c.Serial()}...)
-	tags := append(targetTags, []string{"tinygo", "math_big_pure_go", "gc." + c.GC(), "scheduler." + c.Scheduler(), "serial." + c.Serial()}...)
 	for i := 1; i <= c.GoMinorVersion; i++ {
 		tags = append(tags, fmt.Sprintf("go1.%d", i))
 	}
@@ -552,27 +551,3 @@ type TestConfig struct {
 	BenchMem          bool
 	Shuffle           string
 }
-
-// filterTags removes predefined build tags for a target if a conflicting option
-// is provided by the user.
-func filterTags(targetTags []string, userTags []string) []string {
-	var filtered []string
-	for _, t := range targetTags {
-		switch {
-		case strings.HasPrefix(t, "runtime_memhash_"):
-			overridden := false
-			for _, ut := range userTags {
-				if strings.HasPrefix(ut, "runtime_memhash_") {
-					overridden = true
-					break
-				}
-			}
-			if !overridden {
-				filtered = append(filtered, t)
-			}
-		default:
-			filtered = append(filtered, t)
-		}
-	}
-	return filtered
-}

compileopts/config_test.go

@@ -1,132 +0,0 @@
-package compileopts
-
-import (
-	"fmt"
-	"strings"
-	"testing"
-)
-
-func TestBuildTags(t *testing.T) {
-	tests := []struct {
-		targetTags []string
-		userTags   []string
-		result     []string
-	}{
-		{
-			targetTags: []string{},
-			userTags:   []string{},
-			result: []string{
-				"tinygo",
-				"math_big_pure_go",
-				"gc.conservative",
-				"scheduler.none",
-				"serial.none",
-			},
-		},
-		{
-			targetTags: []string{"bear"},
-			userTags:   []string{},
-			result: []string{
-				"bear",
-				"tinygo",
-				"math_big_pure_go",
-				"gc.conservative",
-				"scheduler.none",
-				"serial.none",
-			},
-		},
-		{
-			targetTags: []string{},
-			userTags:   []string{"cat"},
-			result: []string{
-				"tinygo",
-				"math_big_pure_go",
-				"gc.conservative",
-				"scheduler.none",
-				"serial.none",
-				"cat",
-			},
-		},
-		{
-			targetTags: []string{"bear"},
-			userTags:   []string{"cat"},
-			result: []string{
-				"bear",
-				"tinygo",
-				"math_big_pure_go",
-				"gc.conservative",
-				"scheduler.none",
-				"serial.none",
-				"cat",
-			},
-		},
-		{
-			targetTags: []string{"bear", "runtime_memhash_leveldb"},
-			userTags:   []string{"cat"},
-			result: []string{
-				"bear",
-				"runtime_memhash_leveldb",
-				"tinygo",
-				"math_big_pure_go",
-				"gc.conservative",
-				"scheduler.none",
-				"serial.none",
-				"cat",
-			},
-		},
-		{
-			targetTags: []string{"bear", "runtime_memhash_leveldb"},
-			userTags:   []string{"cat", "runtime_memhash_leveldb"},
-			result: []string{
-				"bear",
-				"tinygo",
-				"math_big_pure_go",
-				"gc.conservative",
-				"scheduler.none",
-				"serial.none",
-				"cat",
-				"runtime_memhash_leveldb",
-			},
-		},
-		{
-			targetTags: []string{"bear", "runtime_memhash_leveldb"},
-			userTags:   []string{"cat", "runtime_memhash_sip"},
-			result: []string{
-				"bear",
-				"tinygo",
-				"math_big_pure_go",
-				"gc.conservative",
-				"scheduler.none",
-				"serial.none",
-				"cat",
-				"runtime_memhash_sip",
-			},
-		},
-	}
-
-	for _, tc := range tests {
-		tt := tc
-		t.Run(fmt.Sprintf("%s+%s", strings.Join(tt.targetTags, ","), strings.Join(tt.userTags, ",")), func(t *testing.T) {
-			c := &Config{
-				Target: &TargetSpec{
-					BuildTags: tt.targetTags,
-				},
-				Options: &Options{
-					Tags: tt.userTags,
-				},
-			}
-
-			res := c.BuildTags()
-
-			if len(res) != len(tt.result) {
-				t.Errorf("expected %d tags, got %d", len(tt.result), len(res))
-			}
-
-			for i, tag := range tt.result {
-				if tag != res[i] {
-					t.Errorf("tag %d: expected %s, got %s", i, tt.result[i], tag)
-				}
-			}
-		})
-	}
-}

src/runtime/memhash_fnv.go

@@ -1,4 +1,7 @@
-//go:build !runtime_memhash_tsip && !runtime_memhash_leveldb
+//go:build (!wasi && !runtime_memhash_tsip && !runtime_memhash_leveldb) || (wasi && runtime_memhash_fnv)
+
+// This is the default for all targets except WASI, unless a more specific build
+// tag is set.
 
 package runtime
 

src/runtime/memhash_leveldb.go

@@ -1,4 +1,7 @@
-//go:build runtime_memhash_leveldb
+//go:build runtime_memhash_leveldb || (wasi && !runtime_memhash_fnv && !runtime_memhash_tsip)
+
+// This is the default for WASI, but can also be used on other targets with the
+// right build tag.
 
 // This is the hash function from Google's leveldb key-value storage system. It
 // processes 4 bytes at a time making it faster than the FNV hash for buffer

targets/wasi.json

@@ -2,7 +2,7 @@
 	"llvm-target":   "wasm32-unknown-wasi",
 	"cpu":           "generic",
 	"features":      "+bulk-memory,+nontrapping-fptoint,+sign-ext",
-	"build-tags":    ["tinygo.wasm", "wasi", "runtime_memhash_leveldb"],
+	"build-tags":    ["tinygo.wasm", "wasi"],
 	"goos":          "linux",
 	"goarch":        "arm",
 	"linker":        "wasm-ld",