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// Copyright 2020 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.
package mvs
import (
"fmt"
"strings"
"golang.org/x/mod/module"
)
// BuildListError decorates an error that occurred gathering requirements
// while constructing a build list. BuildListError prints the chain
// of requirements to the module where the error occurred.
type BuildListError struct {
Err error
stack []buildListErrorElem
}
type buildListErrorElem struct {
m module.Version
// nextReason is the reason this module depends on the next module in the
// stack. Typically either "requires", or "updating to".
nextReason string
}
// NewBuildListError returns a new BuildListError wrapping an error that
// occurred at a module found along the given path of requirements and/or
// upgrades, which must be non-empty.
//
// The isUpgrade function reports whether a path step is due to an upgrade.
// A nil isUpgrade function indicates that none of the path steps are due to upgrades.
func NewBuildListError(err error, path []module.Version, isUpgrade func(from, to module.Version) bool) *BuildListError {
stack := make([]buildListErrorElem, 0, len(path))
for len(path) > 1 {
reason := "requires"
if isUpgrade != nil && isUpgrade(path[0], path[1]) {
reason = "updating to"
}
stack = append(stack, buildListErrorElem{
m: path[0],
nextReason: reason,
})
path = path[1:]
}
stack = append(stack, buildListErrorElem{m: path[0]})
return &BuildListError{
Err: err,
stack: stack,
}
}
// Module returns the module where the error occurred. If the module stack
// is empty, this returns a zero value.
func (e *BuildListError) Module() module.Version {
if len(e.stack) == 0 {
return module.Version{}
}
return e.stack[len(e.stack)-1].m
}
func (e *BuildListError) Error() string {
b := &strings.Builder{}
stack := e.stack
// Don't print modules at the beginning of the chain without a
// version. These always seem to be the main module or a
// synthetic module ("target@").
for len(stack) > 0 && stack[0].m.Version == "" {
stack = stack[1:]
}
if len(stack) == 0 {
b.WriteString(e.Err.Error())
} else {
for _, elem := range stack[:len(stack)-1] {
fmt.Fprintf(b, "%s %s\n\t", elem.m, elem.nextReason)
}
// Ensure that the final module path and version are included as part of the
// error message.
m := stack[len(stack)-1].m
if mErr, ok := e.Err.(*module.ModuleError); ok {
actual := module.Version{Path: mErr.Path, Version: mErr.Version}
if v, ok := mErr.Err.(*module.InvalidVersionError); ok {
actual.Version = v.Version
}
if actual == m {
fmt.Fprintf(b, "%v", e.Err)
} else {
fmt.Fprintf(b, "%s (replaced by %s): %v", m, actual, mErr.Err)
}
} else {
fmt.Fprintf(b, "%v", module.VersionError(m, e.Err))
}
}
return b.String()
}
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