cmd/go: avoid erroneous canonicalization when trying to resolve imports using replacements

Updates #32700
Fixes #33795

Change-Id: I16897a0a2f3aa2f0b0bf8cf8252f3f39eef2e7ba
Reviewed-on: https://go-review.googlesource.com/c/go/+/212200
Run-TryBot: Bryan C. Mills <[email protected]>
Reviewed-by: Jay Conrod <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: Bryan C. Mills

src/cmd/go/internal/modload/import.go

@@ -203,7 +203,12 @@ func Import(path string) (m module.Version, dir string, err error) {
 		latest := map[string]string{} // path -> version
 		for _, r := range modFile.Replace {
 			if maybeInModule(path, r.Old.Path) {
-				latest[r.Old.Path] = semver.Max(r.Old.Version, latest[r.Old.Path])
+				// Don't use semver.Max here; need to preserve +incompatible suffix.
+				v := latest[r.Old.Path]
+				if semver.Compare(r.Old.Version, v) > 0 {
+					v = r.Old.Version
+				}
+				latest[r.Old.Path] = v
 			}
 		}
 

src/cmd/go/testdata/script/mod_replace_import.txt

@@ -54,13 +54,18 @@ replace (
 	example.com/v => ./v
 )
 
+replace (
+	example.com/i v2.0.0+incompatible => ./i2
+)
+
 -- m.go --
 package main
 import (
 	_ "example.com/a/b"
 	_ "example.com/x/v3"
 	_ "example.com/y/z/w"
 	_ "example.com/v"
+	_ "example.com/i"
 )
 func main() {}
 
@@ -115,6 +120,11 @@ module v.localhost
 -- v/v.go --
 package v
 
+-- i2/go.mod --
+module example.com/i
+-- i2/i.go --
+package i
+
 -- fail/m.go --
 package main