internal/lsp: downrank untyped completion candidates

In cases like:

type myInt int
const (
  a       = 1
  b myInt = 2
)
var foo myInt = <>

We now prefer "b" over "a" since b's type matches the expected type
exactly.

Change-Id: I675934761cc17f6b303b63b4715b31dd1af7cea1
Reviewed-on: https://go-review.googlesource.com/c/tools/+/202737
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

internal/lsp/source/completion.go

@@ -1346,7 +1346,15 @@ func (c *completer) matchingCandidate(cand *candidate) bool {
 					// Check that their constant kind (bool|int|float|complex|string) matches.
 					// This doesn't take into account the constant value, so there will be some
 					// false positives due to integer sign and overflow.
-					return candBasic.Info()&types.IsConstType == wantBasic.Info()&types.IsConstType
+					if candBasic.Info()&types.IsConstType == wantBasic.Info()&types.IsConstType {
+						// Lower candidate score if the types are not identical.
+						// This avoids ranking untyped integer constants above
+						// candidates with an exact type match.
+						if !types.Identical(candType, c.expectedType.objType) {
+							cand.score /= 2
+						}
+						return true
+					}
 				}
 				return false
 			}

internal/lsp/testdata/rank/convert_rank.go.in

@@ -12,28 +12,31 @@ func _() {
 }
 
 func _() {
+
+	type myInt int
+
 	const (
 		convC        = "hi"    //@item(convertC, "convC", "string", "const")
 		convD        = 123     //@item(convertD, "convD", "int", "const")
 		convE int    = 123     //@item(convertE, "convE", "int", "const")
 		convF string = "there" //@item(convertF, "convF", "string", "const")
+		convG myInt  = 123     //@item(convertG, "convG", "myInt", "const")
 	)
 
 	var foo int
-	foo = conv //@complete(" //", convertD, convertE, convertC, convertF)
+	foo = conv //@rank(" //", convertE, convertD)
 
-	type myInt int
 	var mi myInt
-	mi = conv //@complete(" //", convertD, convertC, convertE, convertF)
+	mi = conv //@rank(" //", convertG, convertD, convertE)
-	mi + conv //@complete(" //", convertD, convertC, convertE, convertF)
+	mi + conv //@rank(" //", convertG, convertD, convertE)
 
-	1 + conv //@complete(" //", convertD, convertE, convertC, convertF)
+	1 + conv //@rank(" //", convertD, convertE, convertG)
 
 	type myString string
 	var ms myString
-	ms = conv //@complete(" //", convertC, convertD, convertE, convertF)
+	ms = conv //@rank(" //", convertC, convertF)
 
 	type myUint uint32
 	var mu myUint
-	mu = conv //@complete(" //", convertD, convertC, convertE, convertF)
+	mu = conv //@rank(" //", convertD, convertE)
 }

internal/lsp/testdata/summary.txt.golden

@@ -1,10 +1,10 @@
 -- summary --
-CompletionsCount = 219
+CompletionsCount = 213
 CompletionSnippetCount = 39
 UnimportedCompletionsCount = 1
 DeepCompletionsCount = 5
 FuzzyCompletionsCount = 7
-RankedCompletionsCount = 2
+RankedCompletionsCount = 8
 CaseSensitiveCompletionsCount = 4
 DiagnosticsCount = 22
 FoldingRangesCount = 2