1 files changed, 65 insertions, 0 deletions
diff --git a/src/cmd/go/internal/modcmd/fix.go b/src/cmd/go/internal/modcmd/fix.go
new file mode 100644
index 0000000000..bfb51456a6
--- /dev/null
+++ b/src/cmd/go/internal/modcmd/fix.go
@@ -0,0 +1,65 @@
+// Copyright 2018 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.
+
+// go mod fix
+
+package modcmd
+
+import (
+	"cmd/go/internal/base"
+	"cmd/go/internal/modload"
+)
+
+var cmdFix = &base.Command{
+	UsageLine: "go mod fix",
+	Short:     "make go.mod semantically consistent",
+	Long: `
+Fix updates go.mod to use canonical version identifiers and
+to be semantically consistent. For example, consider this go.mod file:
+
+	module M
+
+	require (
+		A v1
+		B v1.0.0
+		C v1.0.0
+		D v1.2.3
+		E dev
+	)
+
+	exclude D v1.2.3
+
+First, fix rewrites non-canonical version identifiers to semver form, so
+A's v1 becomes v1.0.0 and E's dev becomes the pseudo-version for the latest
+commit on the dev branch, perhaps v0.0.0-20180523231146-b3f5c0f6e5f1.
+
+Next, fix updates requirements to respect exclusions, so the requirement
+on the excluded D v1.2.3 is updated to use the next available version of D,
+perhaps D v1.2.4 or D v1.3.0.
+
+Finally, fix removes redundant or misleading requirements.
+For example, if A v1.0.0 itself requires B v1.2.0 and C v1.0.0, then go.mod's
+requirement of B v1.0.0 is misleading (superseded by A's need for v1.2.0),
+and its requirement of C v1.0.0 is redundant (implied by A's need for the
+same version), so both will be removed. If module M contains packages
+that directly import packages from B or C, then the requirements will be
+kept but updated to the actual versions being used.
+
+Although fix runs the fix-up operation in isolation, the fix-up also
+runs automatically any time a go command uses the module graph,
+to update go.mod to reflect reality. Because the module graph defines
+the meaning of import statements, any commands that load packages
+also use and therefore fix the module graph. For example,
+go build, go get, go install, go list, go test, go mod graph, go mod tidy,
+and other commands all effectively imply go mod fix.
+	`,
+	Run: runFix,
+}
+
+func runFix(cmd *base.Command, args []string) {
+	if len(args) != 0 {
+		base.Fatalf("go mod fix: fix takes no arguments")
+	}
+	modload.LoadBuildList() // writes go.mod
+}