cmd/go/internal/modload: add structured errors for queries matching the main module

For #37438

Change-Id: I7df80ae0917b0b4ecad98947da39ddf8554b07c7
Reviewed-on: https://go-review.googlesource.com/c/go/+/266717
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

diff --git a/src/cmd/go/internal/modload/query.go b/src/cmd/go/internal/modload/query.go
index 2e9d72a6bfe0cae7d2ae999c8e605cc0f1f926aa..99cbac1aa79988906f0ba8411a7c3f5f26594ab7 100644 (file)
--- a/src/cmd/go/internal/modload/query.go
+++ b/src/cmd/go/internal/modload/query.go
@@ -109,8 +109,8 @@ func queryProxy(ctx context.Context, proxy, path, query, current string, allowed
        }
 
        if path == Target.Path {
-               if query != "latest" {
-                       return nil, fmt.Errorf("can't query specific version (%q) for the main module (%s)", query, path)
+               if query != "latest" && query != "upgrade" && query != "patch" {
+                       return nil, &QueryMatchesMainModuleError{Pattern: path, Query: query}
                }
                if err := allowed(ctx, Target); err != nil {
                        return nil, fmt.Errorf("internal error: main module version is not allowed: %w", err)
@@ -579,7 +579,11 @@ func QueryPattern(ctx context.Context, pattern, query string, current func(strin
                m := match(Target, modRoot, true)
                if len(m.Pkgs) > 0 {
                        if query != "latest" && query != "upgrade" && query != "patch" {
-                               return nil, nil, fmt.Errorf("can't query version %q for package %s in the main module (%s)", query, pattern, Target.Path)
+                               return nil, nil, &QueryMatchesPackagesInMainModuleError{
+                                       Pattern:  pattern,
+                                       Query:    query,
+                                       Packages: m.Pkgs,
+                               }
                        }
                        if err := allowed(ctx, Target); err != nil {
                                return nil, nil, fmt.Errorf("internal error: package %s is in the main module (%s), but version is not allowed: %w", pattern, Target.Path, err)
@@ -1023,3 +1027,39 @@ func (rr *replacementRepo) replacementStat(v string) (*modfetch.RevInfo, error)
        }
        return rev, nil
 }
+
+// A QueryMatchesMainModuleError indicates that a query requests
+// a version of the main module that cannot be satisfied.
+// (The main module's version cannot be changed.)
+type QueryMatchesMainModuleError struct {
+       Pattern string
+       Query   string
+}
+
+func (e *QueryMatchesMainModuleError) Error() string {
+       if e.Pattern == Target.Path {
+               return fmt.Sprintf("can't request version %q of the main module (%s)", e.Query, e.Pattern)
+       }
+
+       return fmt.Sprintf("can't request version %q of pattern %q that includes the main module (%s)", e.Query, e.Pattern, Target.Path)
+}
+
+// A QueryMatchesPackagesInMainModuleError indicates that a query cannot be
+// satisfied because it matches one or more packages found in the main module.
+type QueryMatchesPackagesInMainModuleError struct {
+       Pattern  string
+       Query    string
+       Packages []string
+}
+
+func (e *QueryMatchesPackagesInMainModuleError) Error() string {
+       if len(e.Packages) > 1 {
+               return fmt.Sprintf("pattern %s matches %d packages in the main module, so can't request version %s", e.Pattern, len(e.Packages), e.Query)
+       }
+
+       if search.IsMetaPackage(e.Pattern) || strings.Contains(e.Pattern, "...") {
+               return fmt.Sprintf("pattern %s matches package %s in the main module, so can't request version %s", e.Pattern, e.Packages[0], e.Query)
+       }
+
+       return fmt.Sprintf("package %s is in the main module, so can't request version %s", e.Packages[0], e.Query)
+}