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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"
)
// 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[V comparable] struct {
Err error
stack []buildListErrorElem[V]
vs Versions[V]
}
type buildListErrorElem[V comparable] struct {
m V
// 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 isVersionChange function reports whether a path step is due to an
// explicit upgrade or downgrade (as opposed to an existing requirement in a
// go.mod file). A nil isVersionChange function indicates that none of the path
// steps are due to explicit version changes.
func NewBuildListError[V comparable](err error, path []V, vs Versions[V], isVersionChange func(from, to V) bool) *BuildListError[V] {
stack := make([]buildListErrorElem[V], 0, len(path))
for len(path) > 1 {
reason := "requires"
if isVersionChange != nil && isVersionChange(path[0], path[1]) {
reason = "updating to"
}
stack = append(stack, buildListErrorElem[V]{
m: path[0],
nextReason: reason,
})
path = path[1:]
}
stack = append(stack, buildListErrorElem[V]{m: path[0]})
return &BuildListError[V]{
Err: err,
stack: stack,
vs: vs,
}
}
// Module returns the module where the error occurred. If the module stack
// is empty, this returns a zero value.
func (e *BuildListError[V]) Module() V {
if len(e.stack) == 0 {
return *new(V)
}
return e.stack[len(e.stack)-1].m
}
func (e *BuildListError[V]) 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 && e.vs.Version(stack[0].m) == "" {
stack = stack[1:]
}
if len(stack) == 0 {
b.WriteString(e.Err.Error())
} else {
for _, elem := range stack[:len(stack)-1] {
fmt.Fprintf(b, "%v %s\n\t", elem.m, elem.nextReason)
}
m := stack[len(stack)-1].m
fmt.Fprintf(b, "%v: %v", m, e.Err)
// TODO the original mvs code was careful to ensure that the final module path
// and version were included as part of the error message, but it did that
// by checking for mod/module-specific error types, but we don't want this
// package to depend on module. We could potentially do it by making those
// errors implement interface types defined in this package.
}
return b.String()
}
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