cmd/go: set default GODEBUG for main packages

For #56986, change the go command to compute and set the
default GODEBUG settings for each main package, based on
the work module's go version and the //go:debug lines in the
main package.

Change-Id: I2118cf0ae6d981138138661e02120c05af648872
Reviewed-on: https://go-review.googlesource.com/c/go/+/453605
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 36 insertions, 35 deletions

diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index 6780c919ae7..084a1046007 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -784,44 +784,45 @@
 // to -f '{{.ImportPath}}'. The struct being passed to the template is:
 //
 //	type Package struct {
-//	    Dir           string   // directory containing package sources
-//	    ImportPath    string   // import path of package in dir
-//	    ImportComment string   // path in import comment on package statement
-//	    Name          string   // package name
-//	    Doc           string   // package documentation string
-//	    Target        string   // install path
-//	    Shlib         string   // the shared library that contains this package (only set when -linkshared)
-//	    Goroot        bool     // is this package in the Go root?
-//	    Standard      bool     // is this package part of the standard Go library?
-//	    Stale         bool     // would 'go install' do anything for this package?
-//	    StaleReason   string   // explanation for Stale==true
-//	    Root          string   // Go root or Go path dir containing this package
-//	    ConflictDir   string   // this directory shadows Dir in $GOPATH
-//	    BinaryOnly    bool     // binary-only package (no longer supported)
-//	    ForTest       string   // package is only for use in named test
-//	    Export        string   // file containing export data (when using -export)
-//	    BuildID       string   // build ID of the compiled package (when using -export)
-//	    Module        *Module  // info about package's containing module, if any (can be nil)
-//	    Match         []string // command-line patterns matching this package
-//	    DepOnly       bool     // package is only a dependency, not explicitly listed
+//	    Dir            string   // directory containing package sources
+//	    ImportPath     string   // import path of package in dir
+//	    ImportComment  string   // path in import comment on package statement
+//	    Name           string   // package name
+//	    Doc            string   // package documentation string
+//	    Target         string   // install path
+//	    Shlib          string   // the shared library that contains this package (only set when -linkshared)
+//	    Goroot         bool     // is this package in the Go root?
+//	    Standard       bool     // is this package part of the standard Go library?
+//	    Stale          bool     // would 'go install' do anything for this package?
+//	    StaleReason    string   // explanation for Stale==true
+//	    Root           string   // Go root or Go path dir containing this package
+//	    ConflictDir    string   // this directory shadows Dir in $GOPATH
+//	    BinaryOnly     bool     // binary-only package (no longer supported)
+//	    ForTest        string   // package is only for use in named test
+//	    Export         string   // file containing export data (when using -export)
+//	    BuildID        string   // build ID of the compiled package (when using -export)
+//	    Module         *Module  // info about package's containing module, if any (can be nil)
+//	    Match          []string // command-line patterns matching this package
+//	    DepOnly        bool     // package is only a dependency, not explicitly listed
+//	    DefaultGODEBUG string  // default GODEBUG setting, for main packages
 //
 //	    // Source files
-//	    GoFiles         []string   // .go source files (excluding CgoFiles, TestGoFiles, XTestGoFiles)
-//	    CgoFiles        []string   // .go source files that import "C"
-//	    CompiledGoFiles []string   // .go files presented to compiler (when using -compiled)
-//	    IgnoredGoFiles  []string   // .go source files ignored due to build constraints
+//	    GoFiles           []string   // .go source files (excluding CgoFiles, TestGoFiles, XTestGoFiles)
+//	    CgoFiles          []string   // .go source files that import "C"
+//	    CompiledGoFiles   []string   // .go files presented to compiler (when using -compiled)
+//	    IgnoredGoFiles    []string   // .go source files ignored due to build constraints
 //	    IgnoredOtherFiles []string // non-.go source files ignored due to build constraints
-//	    CFiles          []string   // .c source files
-//	    CXXFiles        []string   // .cc, .cxx and .cpp source files
-//	    MFiles          []string   // .m source files
-//	    HFiles          []string   // .h, .hh, .hpp and .hxx source files
-//	    FFiles          []string   // .f, .F, .for and .f90 Fortran source files
-//	    SFiles          []string   // .s source files
-//	    SwigFiles       []string   // .swig files
-//	    SwigCXXFiles    []string   // .swigcxx files
-//	    SysoFiles       []string   // .syso object files to add to archive
-//	    TestGoFiles     []string   // _test.go files in package
-//	    XTestGoFiles    []string   // _test.go files outside package
+//	    CFiles            []string   // .c source files
+//	    CXXFiles          []string   // .cc, .cxx and .cpp source files
+//	    MFiles            []string   // .m source files
+//	    HFiles            []string   // .h, .hh, .hpp and .hxx source files
+//	    FFiles            []string   // .f, .F, .for and .f90 Fortran source files
+//	    SFiles            []string   // .s source files
+//	    SwigFiles         []string   // .swig files
+//	    SwigCXXFiles      []string   // .swigcxx files
+//	    SysoFiles         []string   // .syso object files to add to archive
+//	    TestGoFiles       []string   // _test.go files in package
+//	    XTestGoFiles      []string   // _test.go files outside package
 //
 //	    // Embedded files
 //	    EmbedPatterns      []string // //go:embed patterns