cmd/go/internal/modload: cache parsed go.mod files globally

Previously they were cached per mvsReqs instance. However, the
contents of the go.mod file of a given dependency version can only
vary if the 'replace' directives that apply to that version have
changed, and the only time we change 'replace' directives is in 'go
mod edit' (which does not care about the build list or MVS).

This not only simplifies the mvsReqs implementation, but also makes
more of the underlying logic independent of mvsReqs.

For #36460

Change-Id: Ieac20c2fcd56f64d847ac8a1b40f9361ece78663
Reviewed-on: https://go-review.googlesource.com/c/go/+/244774
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 6 insertions, 103 deletions

diff --git a/src/cmd/go/internal/modload/mvs.go b/src/cmd/go/internal/modload/mvs.go
index 873f5891c9..6b6ad945e4 100644
--- a/src/cmd/go/internal/modload/mvs.go
+++ b/src/cmd/go/internal/modload/mvs.go
@@ -6,20 +6,15 @@ package modload
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
 	"sort"
 
-	"cmd/go/internal/base"
-	"cmd/go/internal/cfg"
-	"cmd/go/internal/lockedfile"
 	"cmd/go/internal/modfetch"
 	"cmd/go/internal/mvs"
 	"cmd/go/internal/par"
 
-	"golang.org/x/mod/modfile"
 	"golang.org/x/mod/module"
 	"golang.org/x/mod/semver"
 )
@@ -28,7 +23,7 @@ import (
 // with any exclusions or replacements applied internally.
 type mvsReqs struct {
 	buildList []module.Version
-	cache     par.Cache
+	cache     par.Cache // module.Version → Required method results
 }
 
 // Reqs returns the current module requirement graph.
@@ -42,113 +37,21 @@ func Reqs() mvs.Reqs {
 }
 
 func (r *mvsReqs) Required(mod module.Version) ([]module.Version, error) {
-	type cached struct {
-		list []module.Version
-		err  error
-	}
-
-	c := r.cache.Do(mod, func() interface{} {
-		list, err := r.required(mod)
-		if err != nil {
-			return cached{nil, err}
-		}
-		if index != nil && len(index.exclude) > 0 {
-			// Drop requirements on excluded versions.
-			nonExcluded := list[:0]
-			for _, r := range list {
-				if !index.exclude[r] {
-					nonExcluded = append(nonExcluded, r)
-				}
-			}
-			list = nonExcluded
-		}
-
-		return cached{list, nil}
-	}).(cached)
-
-	return c.list, c.err
-}
-
-func (r *mvsReqs) modFileToList(f *modfile.File) []module.Version {
-	list := make([]module.Version, 0, len(f.Require))
-	for _, r := range f.Require {
-		list = append(list, r.Mod)
-	}
-	return list
-}
-
-// required returns a unique copy of the requirements of mod.
-func (r *mvsReqs) required(mod module.Version) ([]module.Version, error) {
 	if mod == Target {
-		if modFile != nil && modFile.Go != nil {
-			rawGoVersion.LoadOrStore(mod, modFile.Go.Version)
-		}
-		return append([]module.Version(nil), r.buildList[1:]...), nil
-	}
-
-	if cfg.BuildMod == "vendor" {
-		// For every module other than the target,
-		// return the full list of modules from modules.txt.
-		readVendorList()
-		return append([]module.Version(nil), vendorList...), nil
-	}
-
-	origPath := mod.Path
-	if repl := Replacement(mod); repl.Path != "" {
-		if repl.Version == "" {
-			// TODO: need to slip the new version into the tags list etc.
-			dir := repl.Path
-			if !filepath.IsAbs(dir) {
-				dir = filepath.Join(ModRoot(), dir)
-			}
-			gomod := filepath.Join(dir, "go.mod")
-			data, err := lockedfile.Read(gomod)
-			if err != nil {
-				return nil, fmt.Errorf("parsing %s: %v", base.ShortPath(gomod), err)
-			}
-			f, err := modfile.ParseLax(gomod, data, nil)
-			if err != nil {
-				return nil, fmt.Errorf("parsing %s: %v", base.ShortPath(gomod), err)
-			}
-			if f.Go != nil {
-				rawGoVersion.LoadOrStore(repl, f.Go.Version)
-			}
-			return r.modFileToList(f), nil
-		}
-		mod = repl
+		// Use the build list as it existed when r was constructed, not the current
+		// global build list.
+		return r.buildList[1:], nil
 	}
 
 	if mod.Version == "none" {
 		return nil, nil
 	}
 
-	if !semver.IsValid(mod.Version) {
-		// Disallow the broader queries supported by fetch.Lookup.
-		base.Fatalf("go: internal error: %s@%s: unexpected invalid semantic version", mod.Path, mod.Version)
-	}
-
-	data, err := modfetch.GoMod(mod.Path, mod.Version)
+	summary, err := goModSummary(mod)
 	if err != nil {
 		return nil, err
 	}
-	f, err := modfile.ParseLax("go.mod", data, nil)
-	if err != nil {
-		return nil, module.VersionError(mod, fmt.Errorf("parsing go.mod: %v", err))
-	}
-
-	if f.Module == nil {
-		return nil, module.VersionError(mod, errors.New("parsing go.mod: missing module line"))
-	}
-	if mpath := f.Module.Mod.Path; mpath != origPath && mpath != mod.Path {
-		return nil, module.VersionError(mod, fmt.Errorf(`parsing go.mod:
-	module declares its path as: %s
-	        but was required as: %s`, mpath, origPath))
-	}
-	if f.Go != nil {
-		rawGoVersion.LoadOrStore(mod, f.Go.Version)
-	}
-
-	return r.modFileToList(f), nil
+	return summary.require, nil
 }
 
 // Max returns the maximum of v1 and v2 according to semver.Compare.