cmd/go: add and use cmd/go/internal/slices.Clip

This will be part of the standard library soon and then
cmd/go can use it directly, but I am writing a few more instances
of this pattern today and wanted to clean these up first.

Change-Id: I3a7336039949ffe95a403aed08d79206c91eafb7
Reviewed-on: https://go-review.googlesource.com/c/go/+/464115
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>

diff --git a/src/cmd/go/internal/generate/generate.go b/src/cmd/go/internal/generate/generate.go
index 3eda6c71453f16d84acbeac206f15cb94e105c63..160a8723a055f169503e8492a2a24f00c95b01e6 100644 (file)
--- a/src/cmd/go/internal/generate/generate.go
+++ b/src/cmd/go/internal/generate/generate.go
@@ -25,6 +25,7 @@ import (
        "cmd/go/internal/cfg"
        "cmd/go/internal/load"
        "cmd/go/internal/modload"
+       "cmd/go/internal/slices"
        "cmd/go/internal/str"
        "cmd/go/internal/work"
 )
@@ -461,7 +462,7 @@ func (g *Generator) setShorthand(words []string) {
        if g.commands[command] != nil {
                g.errorf("command %q multiply defined", command)
        }
-       g.commands[command] = words[2:len(words):len(words)] // force later append to make copy
+       g.commands[command] = slices.Clip(words[2:])
 }
 
 // exec runs the command specified by the argument. The first word is

diff --git a/src/cmd/go/internal/modload/buildlist.go b/src/cmd/go/internal/modload/buildlist.go
index aa59611e8193acebdaf6aa83d75035dca5ff0be7..fddcdb6b5d82e45e7fecc08e24f2c5aee1636d3b 100644 (file)
--- a/src/cmd/go/internal/modload/buildlist.go
+++ b/src/cmd/go/internal/modload/buildlist.go
@@ -9,6 +9,7 @@ import (
        "cmd/go/internal/cfg"
        "cmd/go/internal/mvs"
        "cmd/go/internal/par"
+       "cmd/go/internal/slices"
        "context"
        "fmt"
        "os"
@@ -23,11 +24,6 @@ import (
        "golang.org/x/mod/semver"
 )
 
-// capVersionSlice returns s with its cap reduced to its length.
-func capVersionSlice(s []module.Version) []module.Version {
-       return s[:len(s):len(s)]
-}
-
 // A Requirements represents a logically-immutable set of root module requirements.
 type Requirements struct {
        // pruning is the pruning at which the requirement graph is computed.
@@ -108,7 +104,7 @@ func newRequirements(pruning modPruning, rootModules []module.Version, direct ma
        if pruning == workspace {
                return &Requirements{
                        pruning:        pruning,
-                       rootModules:    capVersionSlice(rootModules),
+                       rootModules:    slices.Clip(rootModules),
                        maxRootVersion: nil,
                        direct:         direct,
                }
@@ -135,7 +131,7 @@ func newRequirements(pruning modPruning, rootModules []module.Version, direct ma
 
        rs := &Requirements{
                pruning:        pruning,
-               rootModules:    capVersionSlice(rootModules),
+               rootModules:    slices.Clip(rootModules),
                maxRootVersion: make(map[string]string, len(rootModules)),
                direct:         direct,
        }
@@ -470,7 +466,7 @@ func (mg *ModuleGraph) WalkBreadthFirst(f func(m module.Version)) {
 // and may rely on it not to be modified.
 func (mg *ModuleGraph) BuildList() []module.Version {
        mg.buildListOnce.Do(func() {
-               mg.buildList = capVersionSlice(mg.g.BuildList())
+               mg.buildList = slices.Clip(mg.g.BuildList())
        })
        return mg.buildList
 }

diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 34b00d50fa11505461cb1726bf8941456b87db1f..b23966d83a06fb38567c4f042c80f0944457807e 100644 (file)
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -26,6 +26,7 @@ import (
        "cmd/go/internal/modconv"
        "cmd/go/internal/modfetch"
        "cmd/go/internal/search"
+       "cmd/go/internal/slices"
 
        "golang.org/x/mod/modfile"
        "golang.org/x/mod/module"
@@ -990,7 +991,7 @@ func makeMainModules(ms []module.Version, rootDirs []string, modFiles []*modfile
        }
        modRootContainingCWD := findModuleRoot(base.Cwd())
        mainModules := &MainModuleSet{
-               versions:           ms[:len(ms):len(ms)],
+               versions:           slices.Clip(ms),
                inGorootSrc:        map[module.Version]bool{},
                pathPrefix:         map[module.Version]string{},
                modRoot:            map[module.Version]string{},

diff --git a/src/cmd/go/internal/modload/query.go b/src/cmd/go/internal/modload/query.go
index c3764b44133b17f784dda769e8adb4dde4f327e0..4affdc03746524cc5e8e99a9be69df659855b10a 100644 (file)
--- a/src/cmd/go/internal/modload/query.go
+++ b/src/cmd/go/internal/modload/query.go
@@ -23,6 +23,7 @@ import (
        "cmd/go/internal/modfetch/codehost"
        "cmd/go/internal/modinfo"
        "cmd/go/internal/search"
+       "cmd/go/internal/slices"
        "cmd/go/internal/str"
        "cmd/go/internal/trace"
        "cmd/internal/pkgpattern"
@@ -768,7 +769,7 @@ func QueryPattern(ctx context.Context, pattern, query string, current func(strin
                        Query:   query,
                }
        }
-       return results[:len(results):len(results)], modOnly, err
+       return slices.Clip(results), modOnly, err
 }
 
 // modulePrefixesExcludingTarget returns all prefixes of path that may plausibly

diff --git a/src/cmd/go/internal/mvs/graph.go b/src/cmd/go/internal/mvs/graph.go
index c5de4866bf467907bafe5d1370b5f2ed39c8c173..94835bcb3f7a8d93e77a629017e172d9a80c0d51 100644 (file)
--- a/src/cmd/go/internal/mvs/graph.go
+++ b/src/cmd/go/internal/mvs/graph.go
@@ -5,6 +5,7 @@
 package mvs
 
 import (
+       "cmd/go/internal/slices"
        "fmt"
 
        "golang.org/x/mod/module"
@@ -30,7 +31,7 @@ type Graph struct {
 func NewGraph(cmp func(v1, v2 string) int, roots []module.Version) *Graph {
        g := &Graph{
                cmp:      cmp,
-               roots:    roots[:len(roots):len(roots)],
+               roots:    slices.Clip(roots),
                required: make(map[module.Version][]module.Version),
                isRoot:   make(map[module.Version]bool),
                selected: make(map[string]string),
@@ -64,7 +65,7 @@ func (g *Graph) Require(m module.Version, reqs []module.Version) {
 
        // Truncate reqs to its capacity to avoid aliasing bugs if it is later
        // returned from RequiredBy and appended to.
-       reqs = reqs[:len(reqs):len(reqs)]
+       reqs = slices.Clip(reqs)
 
        if _, dup := g.required[m]; dup {
                panic(fmt.Sprintf("requirements of %v have already been set", m))

diff --git a/src/cmd/go/internal/slices/slices.go b/src/cmd/go/internal/slices/slices.go
new file mode 100644 (file)
index 0000000..a0adcf4
--- /dev/null
+++ b/src/cmd/go/internal/slices/slices.go
@@ -0,0 +1,12 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// TODO: Replace with slices package when it lands in standard library.
+
+package slices
+
+// Clip removes unused capacity from the slice, returning s[:len(s):len(s)].
+func Clip[S ~[]E, E any](s S) S {
+       return s[:len(s):len(s)]
+}

diff --git a/src/cmd/go/internal/test/test.go b/src/cmd/go/internal/test/test.go
index be024f44647e74ceaf0f7e2290a3ab5b1ca77482..48760ba914acefd95baf84fd7e9b185b7580c8d5 100644 (file)
--- a/src/cmd/go/internal/test/test.go
+++ b/src/cmd/go/internal/test/test.go
@@ -28,6 +28,7 @@ import (
        "cmd/go/internal/lockedfile"
        "cmd/go/internal/modload"
        "cmd/go/internal/search"
+       "cmd/go/internal/slices"
        "cmd/go/internal/str"
        "cmd/go/internal/trace"
        "cmd/go/internal/work"
@@ -1284,7 +1285,7 @@ func (r *runTestActor) Act(b *work.Builder, ctx context.Context, a *work.Action)
        cmd := exec.CommandContext(ctx, args[0], args[1:]...)
        cmd.Dir = a.Package.Dir
 
-       env := cfg.OrigEnv[:len(cfg.OrigEnv):len(cfg.OrigEnv)]
+       env := slices.Clip(cfg.OrigEnv)
        env = base.AppendPATH(env)
        env = base.AppendPWD(env, cmd.Dir)
        cmd.Env = env

diff --git a/src/cmd/go/internal/vcweb/git.go b/src/cmd/go/internal/vcweb/git.go
index 5f9864e2dd83180251787d06b2ff4e7ac0ec0c27..2168d5215683388643cd11fb4922133b545cd13d 100644 (file)
--- a/src/cmd/go/internal/vcweb/git.go
+++ b/src/cmd/go/internal/vcweb/git.go
@@ -5,6 +5,7 @@
 package vcweb
 
 import (
+       "cmd/go/internal/slices"
        "log"
        "net/http"
        "net/http/cgi"
@@ -41,7 +42,7 @@ func (h *gitHandler) Handler(dir string, env []string, logger *log.Logger) (http
                Logger: logger,
                Args:   []string{"http-backend"},
                Dir:    dir,
-               Env: append(env[:len(env):len(env)],
+               Env: append(slices.Clip(env),
                        "GIT_PROJECT_ROOT="+dir,
                        "GIT_HTTP_EXPORT_ALL=1",
                ),

diff --git a/src/cmd/go/internal/vcweb/hg.go b/src/cmd/go/internal/vcweb/hg.go
index 86871710d114f3157e617b6fa185bbbe18b6548f..3c45acab3e9f37ad0b8fbee84b046b1146f01398 100644 (file)
--- a/src/cmd/go/internal/vcweb/hg.go
+++ b/src/cmd/go/internal/vcweb/hg.go
@@ -6,6 +6,7 @@ package vcweb
 
 import (
        "bufio"
+       "cmd/go/internal/slices"
        "context"
        "errors"
        "io"
@@ -54,7 +55,7 @@ func (h *hgHandler) Handler(dir string, env []string, logger *log.Logger) (http.
 
                cmd := exec.CommandContext(ctx, h.hgPath, "serve", "--port", "0", "--address", "localhost", "--accesslog", os.DevNull, "--name", "vcweb", "--print-url")
                cmd.Dir = dir
-               cmd.Env = append(env[:len(env):len(env)], "PWD="+dir)
+               cmd.Env = append(slices.Clip(env), "PWD="+dir)
 
                cmd.Cancel = func() error {
                        err := cmd.Process.Signal(os.Interrupt)

diff --git a/src/cmd/go/internal/work/exec.go b/src/cmd/go/internal/work/exec.go
index 7f2924f73d5055ccbfcd6333c25d58ce7a7928c1..8dde0a9e06412792700ab73079129a848d342941 100644 (file)
--- a/src/cmd/go/internal/work/exec.go
+++ b/src/cmd/go/internal/work/exec.go
@@ -36,6 +36,7 @@ import (
        "cmd/go/internal/fsys"
        "cmd/go/internal/load"
        "cmd/go/internal/modload"
+       "cmd/go/internal/slices"
        "cmd/go/internal/str"
        "cmd/go/internal/trace"
        "cmd/internal/quoted"
@@ -2490,7 +2491,7 @@ func (b *Builder) ccompile(a *Action, p *load.Package, outfile string, flags []s
                        } else {
                                to = filepath.Join("/_", toPath)
                        }
-                       flags = append(flags[:len(flags):len(flags)], "-fdebug-prefix-map="+from+"="+to)
+                       flags = append(slices.Clip(flags), "-fdebug-prefix-map="+from+"="+to)
                }
        }