internal/astinternal: don't panic on nil pointers in DebugPrint

For example, on an unnamed import, whose ImportSpec.Name *Ident is nil.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: Ica114ad96defb35fa8b86b31c9686d2e5750c066
Dispatch-Trailer: {"type":"trybot","CL":1199936,"patchset":1,"ref":"refs/changes/36/1199936/1","targetBranch":"master"}

internal/astinternal/debug.go

@@ -58,16 +58,21 @@ func (d *debugPrinter) value(v reflect.Value, impliedType reflect.Type) {
 	if v.Kind() == reflect.Interface {
 		v = v.Elem()
 	}
-
-	// Indirecting a nil interface/pointer gives a zero value;
-	// stop as calling reflect.Value.Type on an invalid type would panic.
+	// Indirecting a nil interface gives a zero value.
 	if !v.IsValid() {
 		d.printf("nil")
 		return
 	}
+
 	// We print the original pointer type if there was one.
 	origType := v.Type()
+
 	v = reflect.Indirect(v)
+	// Indirecting a nil pointer gives a zero value.
+	if !v.IsValid() {
+		d.printf("nil")
+		return
+	}
 
 	t := v.Type()
 	switch t {

internal/astinternal/testdata/debugprint/file.txtar

@@ -4,6 +4,15 @@ package p
 -- comments_only.cue --
 // some
 // comment lines
+-- imports.cue --
+package p
+
+import "foo"
+
+import (
+	"bar"
+	name "baz"
+)
 -- out/debugprint/empty.cue --
 *ast.File{
 	Filename: "empty.cue"
@@ -47,3 +56,92 @@ package p
 		}
 	}
 }
+-- out/debugprint/imports.cue --
+*ast.File{
+	Filename: "imports.cue"
+	Decls: []ast.Decl{
+		*ast.Package{
+			PackagePos: token.Pos("imports.cue:1:1")
+			Name: *ast.Ident{
+				NamePos: token.Pos("imports.cue:1:9")
+				Name: "p"
+			}
+		}
+		*ast.ImportDecl{
+			Import: token.Pos("imports.cue:3:1")
+			Lparen: token.Pos("-")
+			Specs: []*ast.ImportSpec{
+				{
+					Name: nil
+					Path: *ast.BasicLit{
+						ValuePos: token.Pos("imports.cue:3:8")
+						Kind: token.Token("STRING")
+						Value: "\"foo\""
+					}
+					EndPos: token.Pos("-")
+				}
+			}
+			Rparen: token.Pos("-")
+		}
+		*ast.ImportDecl{
+			Import: token.Pos("imports.cue:5:1")
+			Lparen: token.Pos("imports.cue:5:8")
+			Specs: []*ast.ImportSpec{
+				{
+					Name: nil
+					Path: *ast.BasicLit{
+						ValuePos: token.Pos("imports.cue:6:2")
+						Kind: token.Token("STRING")
+						Value: "\"bar\""
+					}
+					EndPos: token.Pos("-")
+				}
+				{
+					Name: *ast.Ident{
+						NamePos: token.Pos("imports.cue:7:2")
+						Name: "name"
+					}
+					Path: *ast.BasicLit{
+						ValuePos: token.Pos("imports.cue:7:7")
+						Kind: token.Token("STRING")
+						Value: "\"baz\""
+					}
+					EndPos: token.Pos("-")
+				}
+			}
+			Rparen: token.Pos("imports.cue:8:1")
+		}
+	}
+	Imports: []*ast.ImportSpec{
+		{
+			Name: nil
+			Path: *ast.BasicLit{
+				ValuePos: token.Pos("imports.cue:3:8")
+				Kind: token.Token("STRING")
+				Value: "\"foo\""
+			}
+			EndPos: token.Pos("-")
+		}
+		{
+			Name: nil
+			Path: *ast.BasicLit{
+				ValuePos: token.Pos("imports.cue:6:2")
+				Kind: token.Token("STRING")
+				Value: "\"bar\""
+			}
+			EndPos: token.Pos("-")
+		}
+		{
+			Name: *ast.Ident{
+				NamePos: token.Pos("imports.cue:7:2")
+				Name: "name"
+			}
+			Path: *ast.BasicLit{
+				ValuePos: token.Pos("imports.cue:7:7")
+				Kind: token.Token("STRING")
+				Value: "\"baz\""
+			}
+			EndPos: token.Pos("-")
+		}
+	}
+}