cmd/compile: have all or no parameter named in exported signatures

Binary export format only.

Make sure we don't accidentally export an unnamed parameter
in signatures which expect all named parameters; otherwise
we crash during import. Appears to happen for _ (blank)
parameter names, as observed in method signatures such as
the one at: x/tools/godoc/analysis/analysis.go:76.

Fixes #15470.

TBR=mdempsky

Change-Id: I1b1184bf08c4c09d8a46946539c4b8c341acdb84
Reviewed-on: https://go-review.googlesource.com/22543
Reviewed-by: Robert Griesemer <gri@golang.org>

diff --git a/src/cmd/compile/internal/gc/bexport.go b/src/cmd/compile/internal/gc/bexport.go
index 9c5d8bd4f8bf2aef15b9f40b81b517cd009d9004..20c1aeba9dc4860de9e5a5af0144551fcc946837 100644 (file)
--- a/src/cmd/compile/internal/gc/bexport.go
+++ b/src/cmd/compile/internal/gc/bexport.go
@@ -819,19 +819,30 @@ func (p *exporter) param(q *Field, n int, numbered bool) {
        }
        p.typ(t)
        if n > 0 {
-               p.string(parName(q, numbered))
-               // Because of (re-)exported inlined functions
-               // the importpkg may not be the package to which this
-               // function (and thus its parameter) belongs. We need to
-               // supply the parameter package here. We need the package
-               // when the function is inlined so we can properly resolve
-               // the name.
-               // TODO(gri) This is compiler-specific. Try using importpkg
-               // here and then update the symbols if we find an inlined
-               // body only. Otherwise, the parameter name is ignored and
-               // the package doesn't matter. This would remove an int
-               // (likely 1 byte) for each named parameter.
-               p.pkg(q.Sym.Pkg)
+               if name := parName(q, numbered); name != "" {
+                       p.string(name)
+                       // Because of (re-)exported inlined functions
+                       // the importpkg may not be the package to which this
+                       // function (and thus its parameter) belongs. We need to
+                       // supply the parameter package here. We need the package
+                       // when the function is inlined so we can properly resolve
+                       // the name.
+                       // TODO(gri) This is compiler-specific. Try using importpkg
+                       // here and then update the symbols if we find an inlined
+                       // body only. Otherwise, the parameter name is ignored and
+                       // the package doesn't matter. This would remove an int
+                       // (likely 1 byte) for each named parameter.
+                       p.pkg(q.Sym.Pkg)
+               } else {
+                       // Sometimes we see an empty name even for n > 0.
+                       // This appears to happen for interface methods
+                       // with _ (blank) parameter names. Make sure we
+                       // have a proper name and package so we don't crash
+                       // during import (see also issue #15470).
+                       // TODO(gri) review parameter encoding
+                       p.string("_")
+                       p.pkg(localpkg)
+               }
        }
        // TODO(gri) This is compiler-specific (escape info).
        // Move into compiler-specific section eventually?