cmd/go: include packages with InvalidGoFiles when filtering main packages

If a package has files with conflicting package names, go/build
empirically populates the first name encountered and puts the
remaining files in InvalidGoFiles. That foiled our check for packages
whose name is either unpopulated or "main", since the "package main"
could be found in a source file after the first.

Instead, we now treat any package with a nonzero set of InvalidGoFiles
as potentially a main package. This biases toward over-reporting
errors, but we would rather over-report than under-report.

If we fix #45999, we will be able to make these error checks more
precise.

Updates #42088
Fixes #45827
Fixes #39986

Change-Id: I588314341b17961b38660192c2130678dc03023e
Reviewed-on: https://go-review.googlesource.com/c/go/+/317300
Trust: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/load/pkg.go

@@ -87,6 +87,7 @@ type PackagePublic struct {
 	CgoFiles          []string `json:",omitempty"` // .go source files that import "C"
 	CompiledGoFiles   []string `json:",omitempty"` // .go output from running cgo on CgoFiles
 	IgnoredGoFiles    []string `json:",omitempty"` // .go source files ignored due to build constraints
+	InvalidGoFiles    []string `json:",omitempty"` // .go source files with detected problems (parse error, wrong package name, and so on)
 	IgnoredOtherFiles []string `json:",omitempty"` // non-.go source files ignored due to build constraints
 	CFiles            []string `json:",omitempty"` // .c source files
 	CXXFiles          []string `json:",omitempty"` // .cc, .cpp and .cxx source files
@@ -144,6 +145,7 @@ func (p *Package) AllFiles() []string {
 		p.CgoFiles,
 		// no p.CompiledGoFiles, because they are from GoFiles or generated by us
 		p.IgnoredGoFiles,
+		// no p.InvalidGoFiles, because they are from GoFiles
 		p.IgnoredOtherFiles,
 		p.CFiles,
 		p.CXXFiles,
@@ -371,6 +373,7 @@ func (p *Package) copyBuild(opts PackageOpts, pp *build.Package) {
 	p.GoFiles = pp.GoFiles
 	p.CgoFiles = pp.CgoFiles
 	p.IgnoredGoFiles = pp.IgnoredGoFiles
+	p.InvalidGoFiles = pp.InvalidGoFiles
 	p.IgnoredOtherFiles = pp.IgnoredOtherFiles
 	p.CFiles = pp.CFiles
 	p.CXXFiles = pp.CXXFiles
@@ -2493,7 +2496,7 @@ func PackagesAndErrors(ctx context.Context, opts PackageOpts, patterns []string)
 	}
 
 	if opts.MainOnly {
-		pkgs = mainPackagesOnly(pkgs, patterns)
+		pkgs = mainPackagesOnly(pkgs, matches)
 	}
 
 	// Now that CmdlinePkg is set correctly,
@@ -2547,50 +2550,63 @@ func CheckPackageErrors(pkgs []*Package) {
 // mainPackagesOnly filters out non-main packages matched only by arguments
 // containing "..." and returns the remaining main packages.
 //
+// Packages with missing, invalid, or ambiguous names may be treated as
+// possibly-main packages.
+//
 // mainPackagesOnly sets a non-main package's Error field and returns it if it
 // is named by a literal argument.
 //
 // mainPackagesOnly prints warnings for non-literal arguments that only match
 // non-main packages.
-func mainPackagesOnly(pkgs []*Package, patterns []string) []*Package {
+func mainPackagesOnly(pkgs []*Package, matches []*search.Match) []*Package {
-	matchers := make([]func(string) bool, len(patterns))
+	treatAsMain := map[string]bool{}
-	for i, p := range patterns {
+	for _, m := range matches {
-		if strings.Contains(p, "...") {
+		if m.IsLiteral() {
-			matchers[i] = search.MatchPattern(p)
+			for _, path := range m.Pkgs {
+				treatAsMain[path] = true
+			}
 		}
 	}
 
-	matchedPkgs := make([]*Package, 0, len(pkgs))
+	var mains []*Package
-	mainCount := make([]int, len(patterns))
-	nonMainCount := make([]int, len(patterns))
 	for _, pkg := range pkgs {
-		if pkg.Name == "main" || (pkg.Incomplete && pkg.Name == "") {
+		if pkg.Name == "main" {
-			matchedPkgs = append(matchedPkgs, pkg)
+			treatAsMain[pkg.ImportPath] = true
-			for i := range patterns {
+			mains = append(mains, pkg)
-				if matchers[i] != nil && matchers[i](pkg.ImportPath) {
+			continue
-					mainCount[i]++
 		}
+
+		if len(pkg.InvalidGoFiles) > 0 { // TODO(#45999): && pkg.Name == "", but currently go/build sets pkg.Name arbitrarily if it is ambiguous.
+			// The package has (or may have) conflicting names, and we can't easily
+			// tell whether one of them is "main". So assume that it could be, and
+			// report an error for the package.
+			treatAsMain[pkg.ImportPath] = true
 		}
-		} else {
+		if treatAsMain[pkg.ImportPath] {
-			for i := range patterns {
-				if matchers[i] == nil && patterns[i] == pkg.ImportPath {
 			if pkg.Error == nil {
 				pkg.Error = &PackageError{Err: &mainPackageError{importPath: pkg.ImportPath}}
 			}
-					matchedPkgs = append(matchedPkgs, pkg)
+			mains = append(mains, pkg)
-				} else if matchers[i] != nil && matchers[i](pkg.ImportPath) {
-					nonMainCount[i]++
-				}
-			}
-		}
-	}
-	for i, p := range patterns {
-		if matchers[i] != nil && mainCount[i] == 0 && nonMainCount[i] > 0 {
-			fmt.Fprintf(os.Stderr, "go: warning: %q matched no main packages\n", p)
 		}
 	}
 
-	return matchedPkgs
+	for _, m := range matches {
+		if m.IsLiteral() || len(m.Pkgs) == 0 {
+			continue
+		}
+		foundMain := false
+		for _, path := range m.Pkgs {
+			if treatAsMain[path] {
+				foundMain = true
+				break
+			}
+		}
+		if !foundMain {
+			fmt.Fprintf(os.Stderr, "go: warning: %q matched only non-main packages\n", m.Pattern())
+		}
+	}
+
+	return mains
 }
 
 type mainPackageError struct {

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

@@ -143,7 +143,7 @@ stderr '^go: warning: "example.com/cmd/nomatch\.\.\." matched no packages$'
 
 # If a wildcard matches only non-main packges, we should see a different warning.
 go install example.com/cmd/err...@v1.0.0
-stderr '^go: warning: "example.com/cmd/err\.\.\." matched no main packages$'
+stderr '^go: warning: "example.com/cmd/err\.\.\." matched only non-main packages$'
 
 
 # 'go install pkg@version' should report errors if the module contains

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

@@ -0,0 +1,18 @@
+! go run $PWD
+! stderr 'no packages loaded'
+stderr '^package example.net/nonmain is not a main package$'
+
+! go run .
+stderr '^package example.net/nonmain is not a main package$'
+
+! go run ./...
+stderr '^go: warning: "\./\.\.\." matched only non-main packages$'
+stderr '^go run: no packages loaded from \./\.\.\.$'
+
+-- go.mod --
+module example.net/nonmain
+
+go 1.17
+-- nonmain.go --
+// Package nonmain is not a main package.
+package nonmain

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

@@ -1,12 +1,26 @@
+# https://golang.org/issue/39986: files reported as invalid by go/build should
+# be listed in InvalidGoFiles.
+
+go list -e -f '{{.Incomplete}}{{"\n"}}{{.Error}}{{"\n"}}{{.InvalidGoFiles}}{{"\n"}}' .
+stdout '^true\nfound packages m \(m\.go\) and main \(main\.go\) in '$PWD'\n\[main.go\]\n'
+
+
 # https://golang.org/issue/45827: 'go run .' should report the same package
-# errors as 'go build'.
+# errors as 'go build' and 'go list'.
 
 ! go build
 stderr '^found packages m \(m\.go\) and main \(main\.go\) in '$PWD'$'
 
+! go list .
+stderr '^found packages m \(m\.go\) and main \(main\.go\) in '$PWD'$'
+
 ! go run .
-	# TODO(#45827): This error should match the above.
+! stderr 'no packages loaded'
-stderr '^go run: no packages loaded from \.$'
+stderr '^found packages m \(m\.go\) and main \(main\.go\) in '$PWD'$'
+
+! go run ./...
+! stderr 'no packages loaded'
+stderr '^found packages m \(m\.go\) and main \(main\.go\) in '$PWD'$'
 
 -- go.mod --
 module m