go/ast/astutil: describe fewer CallExprs as "conversions"

Only unary CallExprs with no ellipsis, f(x), are ambiguous.

Change-Id: If4f17445ab0725dee916992db133eac5536133a7
Reviewed-on: https://go-review.googlesource.com/24552
Reviewed-by: Robert Griesemer <gri@golang.org>

cmd/guru/testdata/src/describe/main.golden

@@ -206,7 +206,7 @@ Fields:
 	inner.recursive.E bool
 
 -------- @describe call-unknown --------
-function call (or conversion) of type invalid type
+function call of type invalid type
 
 -------- @describe def-iface-I --------
 definition of type I (size 16, align 8)

cmd/guru/testdata/src/what-json/main.golden

@@ -7,7 +7,7 @@
 			"end": 176
 		},
 		{
-			"desc": "function call (or conversion)",
+			"desc": "function call",
 			"start": 175,
 			"end": 178
 		},

cmd/guru/testdata/src/what/main.golden

@@ -7,7 +7,7 @@ import path: what
 
 -------- @what call --------
 identifier
-function call (or conversion)
+function call
 expression statement
 block
 function declaration

go/ast/astutil/enclosing.go

@@ -509,7 +509,10 @@ func NodeDescription(n ast.Node) string {
 			return "fall-through statement"
 		}
 	case *ast.CallExpr:
+		if len(n.Args) == 1 && !n.Ellipsis.IsValid() {
 			return "function call (or conversion)"
+		}
+		return "function call"
 	case *ast.CaseClause:
 		return "case clause"
 	case *ast.ChanType:

oracle/testdata/src/what-json/main.golden

@@ -9,7 +9,7 @@
 				"end": 180
 			},
 			{
-				"desc": "function call (or conversion)",
+				"desc": "function call",
 				"start": 179,
 				"end": 182
 			},

oracle/testdata/src/what/main.golden

@@ -7,7 +7,7 @@ import path: what
 
 -------- @what call --------
 identifier
-function call (or conversion)
+function call
 expression statement
 block
 function declaration