Add ChunkMatch.BestLineMatch to return the best-scoring line (sourcegraph#884)

This PR adds a new field `ChunkMatch.BestLineMatch` with the line number of top-scoring line in the chunk. This will let us address a long-standing issue with our new flexible keyword search, where chunk matches can become very large. Since our search results UX only shows the start of a chunk, the most relevant line may not even be visible. With this information on the best line match, we can adjust the search results UX to center the chunk on the most relevant line.

Relates to [SPLF-188](https://linear.app/sourcegraph/issue/SPLF-188/ensure-the-best-scoring-line-match-is-shown-in-search-results)

Author: jtibshirani

api.go

@@ -161,7 +161,13 @@ type ChunkMatch struct {
 	// beginning of a line (Column will always be 1).
 	ContentStart Location
 
+	// Score is the overall relevance score of this chunk.
 	Score float64
+
+	// BestLineMatch is the line number of the highest-scoring line match in this chunk.
+	// The line number represents the index in the full file, and is 1-based. If FileName: true,
+	// this number will be 0.
+	BestLineMatch uint32
 }
 
 func (cm *ChunkMatch) sizeBytes() (sz uint64) {

api_proto.go

@@ -96,13 +96,14 @@ func ChunkMatchFromProto(p *proto.ChunkMatch) ChunkMatch {
 	}
 
 	return ChunkMatch{
-		Content:      p.GetContent(),
-		ContentStart: LocationFromProto(p.GetContentStart()),
-		FileName:     p.GetFileName(),
-		Ranges:       ranges,
-		SymbolInfo:   symbols,
-		Score:        p.GetScore(),
-		DebugScore:   p.GetDebugScore(),
+		Content:       p.GetContent(),
+		ContentStart:  LocationFromProto(p.GetContentStart()),
+		FileName:      p.GetFileName(),
+		Ranges:        ranges,
+		SymbolInfo:    symbols,
+		Score:         p.GetScore(),
+		BestLineMatch: p.GetBestLineMatch(),
+		DebugScore:    p.GetDebugScore(),
 	}
 }
 
@@ -118,13 +119,14 @@ func (cm *ChunkMatch) ToProto() *proto.ChunkMatch {
 	}
 
 	return &proto.ChunkMatch{
-		Content:      cm.Content,
-		ContentStart: cm.ContentStart.ToProto(),
-		FileName:     cm.FileName,
-		Ranges:       ranges,
-		SymbolInfo:   symbolInfo,
-		Score:        cm.Score,
-		DebugScore:   cm.DebugScore,
+		Content:       cm.Content,
+		ContentStart:  cm.ContentStart.ToProto(),
+		FileName:      cm.FileName,
+		Ranges:        ranges,
+		SymbolInfo:    symbolInfo,
+		Score:         cm.Score,
+		BestLineMatch: cm.BestLineMatch,
+		DebugScore:    cm.DebugScore,
 	}
 }
 

api_test.go

@@ -149,7 +149,7 @@ func TestMatchSize(t *testing.T) {
 		size: 256,
 	}, {
 		v:    ChunkMatch{},
-		size: 112,
+		size: 120,
 	}, {
 		v:    candidateMatch{},
 		size: 80,

build/scoring_test.go

@@ -27,11 +27,12 @@ import (
 )
 
 type scoreCase struct {
-	fileName  string
-	content   []byte
-	query     query.Q
-	language  string
-	wantScore float64
+	fileName          string
+	content           []byte
+	query             query.Q
+	language          string
+	wantScore         float64
+	wantBestLineMatch uint32
 }
 
 func TestFileNameMatch(t *testing.T) {
@@ -79,6 +80,8 @@ func TestBM25(t *testing.T) {
 			language: "Java",
 			// bm25-score: 0.58 <- sum-termFrequencyScore: 14.00, length-ratio: 1.00
 			wantScore: 0.58,
+			// line 5:    private final int exampleField;
+			wantBestLineMatch: 5,
 		}, {
 			// Matches only on content
 			fileName: "example.java",
@@ -91,6 +94,8 @@ func TestBM25(t *testing.T) {
 			language: "Java",
 			// bm25-score: 1.81 <- sum-termFrequencyScore: 116.00, length-ratio: 1.00
 			wantScore: 1.81,
+			// line 3: public class InnerClasses {
+			wantBestLineMatch: 3,
 		},
 		{
 			// Matches only on filename
@@ -130,6 +135,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 5500 (partial symbol at boundary) + 1000 (Java class) + 50 (partial word)
 			wantScore: 6550,
+			// line 37: public class InnerClass implements InnerInterface<Integer, Integer> {
+			wantBestLineMatch: 37,
 		},
 		{
 			fileName: "example.java",
@@ -138,6 +145,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 5500 (partial symbol at boundary) + 1000 (Java class) + 500 (word)
 			wantScore: 7000,
+			// line 32:   public static class InnerStaticClass {
+			wantBestLineMatch: 32,
 		},
 		{
 			fileName: "example.java",
@@ -146,6 +155,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 7000 (symbol) + 900 (Java enum) + 500 (word)
 			wantScore: 8400,
+			// line 16:   public enum InnerEnum {
+			wantBestLineMatch: 16,
 		},
 		{
 			fileName: "example.java",
@@ -154,6 +165,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 7000 (symbol) + 800 (Java interface) + 500 (word)
 			wantScore: 8300,
+			// line 22:     public interface InnerInterface<A, B> {
+			wantBestLineMatch: 22,
 		},
 		{
 			fileName: "example.java",
@@ -162,6 +175,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 7000 (symbol) + 700 (Java method) + 500 (word)
 			wantScore: 8200,
+			// line 44:     public void innerMethod() {
+			wantBestLineMatch: 44,
 		},
 		{
 			fileName: "example.java",
@@ -170,6 +185,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 7000 (symbol) + 600 (Java field) + 500 (word)
 			wantScore: 8100,
+			// line 38:     private final int field;
+			wantBestLineMatch: 38,
 		},
 		{
 			fileName: "example.java",
@@ -178,6 +195,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 7000 (symbol) + 500 (Java enum constant) + 500 (word)
 			wantScore: 8000,
+			// line 18:     B,
+			wantBestLineMatch: 18,
 		},
 		// 2 Atoms (1x content and 1x filename)
 		{
@@ -187,6 +206,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 5500 (edge symbol) + 600 (Java field) + 500 (word) + 200 (atom)
 			wantScore: 6800,
+			// line 5:   private final int exampleField;
+			wantBestLineMatch: 5,
 		},
 		// 3 Atoms (2x content, 1x filename)
 		{
@@ -199,6 +220,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 7000 (symbol) + 700 (Java method) + 500 (word) + 266.67 (atom)
 			wantScore: 8466,
+			// line 54:   private static <A, B> B runInnerInterface(InnerInterface<A, B> fn, A a) {
+			wantBestLineMatch: 54,
 		},
 		// 4 Atoms (4x content)
 		{
@@ -213,6 +236,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 7000 (symbol) + 900 (Java enum) + 500 (word) + 300 (atom)
 			wantScore: 8700,
+			// line 16:   public enum InnerEnum {
+			wantBestLineMatch: 16,
 		},
 		{
 			fileName: "example.java",
@@ -221,6 +246,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 4000 (overlap Symbol) + 700 (Java method) + 50 (partial word)
 			wantScore: 4750,
+			// line 54:   private static <A, B> B runInnerInterface(InnerInterface<A, B> fn, A a) {
+			wantBestLineMatch: 54,
 		},
 		{
 			fileName: "example.java",
@@ -229,6 +256,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 7000 (Symbol) + 900 (Java enum) + 500 (word)
 			wantScore: 8400,
+			// line 16:   public enum InnerEnum {
+			wantBestLineMatch: 16,
 		},
 		{
 			fileName: "example.java",
@@ -237,6 +266,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 5500 (edge Symbol) + 900 (Java enum) + 500 (word)
 			wantScore: 6900,
+			// line 16:   public enum InnerEnum {
+			wantBestLineMatch: 16,
 		},
 		{
 			fileName: "example.java",
@@ -245,6 +276,8 @@ func TestJava(t *testing.T) {
 			language: "Java",
 			// 4000 (overlap Symbol) + 900 (Java enum) + 500 (word)
 			wantScore: 5400,
+			// line 16:   public enum InnerEnum {
+			wantBestLineMatch: 16,
 		},
 	}
 
@@ -640,6 +673,16 @@ func checkScoring(t *testing.T, c scoreCase, useBM25 bool, parserType ctags.CTag
 			t.Fatalf("score: want %f, got %f\ndebug: %s\ndebugscore: %s", c.wantScore, got, srs.Files[0].Debug, srs.Files[0].ChunkMatches[0].DebugScore)
 		}
 
+		if c.wantBestLineMatch != 0 {
+			if len(srs.Files[0].ChunkMatches) == 0 {
+				t.Fatalf("want BestLineMatch %d, but no chunk matches were returned", c.wantBestLineMatch)
+			}
+			chunkMatch := srs.Files[0].ChunkMatches[0]
+			if chunkMatch.BestLineMatch != c.wantBestLineMatch {
+				t.Fatalf("want BestLineMatch %d, got %d", c.wantBestLineMatch, chunkMatch.BestLineMatch)
+			}
+		}
+
 		if got := srs.Files[0].Language; got != c.language {
 			t.Fatalf("want %s, got %s", c.language, got)
 		}