mvdan.cc
1// Copyright 2020 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package mvs
6
7import (
8 "fmt"
9 "strings"
10)
11
12// BuildListError decorates an error that occurred gathering requirements
13// while constructing a build list. BuildListError prints the chain
14// of requirements to the module where the error occurred.
15type BuildListError[V comparable] struct {
16 Err error
17 stack []buildListErrorElem[V]
18 vs Versions[V]
19}
20
21type buildListErrorElem[V comparable] struct {
22 m V
23
24 // nextReason is the reason this module depends on the next module in the
25 // stack. Typically either "requires", or "updating to".
26 nextReason string
27}
28
29// NewBuildListError returns a new BuildListError wrapping an error that
30// occurred at a module found along the given path of requirements and/or
31// upgrades, which must be non-empty.
32//
33// The isVersionChange function reports whether a path step is due to an
34// explicit upgrade or downgrade (as opposed to an existing requirement in a
35// go.mod file). A nil isVersionChange function indicates that none of the path
36// steps are due to explicit version changes.
37func NewBuildListError[V comparable](err error, path []V, vs Versions[V], isVersionChange func(from, to V) bool) *BuildListError[V] {
38 stack := make([]buildListErrorElem[V], 0, len(path))
39 for len(path) > 1 {
40 reason := "requires"
41 if isVersionChange != nil && isVersionChange(path[0], path[1]) {
42 reason = "updating to"
43 }
44 stack = append(stack, buildListErrorElem[V]{
45 m: path[0],
46 nextReason: reason,
47 })
48 path = path[1:]
49 }
50 stack = append(stack, buildListErrorElem[V]{m: path[0]})
51
52 return &BuildListError[V]{
53 Err: err,
54 stack: stack,
55 vs: vs,
56 }
57}
58
59// Module returns the module where the error occurred. If the module stack
60// is empty, this returns a zero value.
61func (e *BuildListError[V]) Module() V {
62 if len(e.stack) == 0 {
63 return *new(V)
64 }
65 return e.stack[len(e.stack)-1].m
66}
67
68func (e *BuildListError[V]) Error() string {
69 b := &strings.Builder{}
70 stack := e.stack
71
72 // Don't print modules at the beginning of the chain without a
73 // version. These always seem to be the main module or a
74 // synthetic module ("target@").
75 for len(stack) > 0 && e.vs.Version(stack[0].m) == "" {
76 stack = stack[1:]
77 }
78
79 if len(stack) == 0 {
80 b.WriteString(e.Err.Error())
81 } else {
82 for _, elem := range stack[:len(stack)-1] {
83 fmt.Fprintf(b, "%v %s\n\t", elem.m, elem.nextReason)
84 }
85 m := stack[len(stack)-1].m
86 fmt.Fprintf(b, "%v: %v", m, e.Err)
87 // TODO the original mvs code was careful to ensure that the final module path
88 // and version were included as part of the error message, but it did that
89 // by checking for mod/module-specific error types, but we don't want this
90 // package to depend on module. We could potentially do it by making those
91 // errors implement interface types defined in this package.
92 }
93 return b.String()
94}