gopls/internal/mcp: report one-based reference line numbers

formatReferences currently embeds zero-based LSP line numbers in its
human-readable output. This causes, for example, a declaration on the
third source line to be reported as being on line 2.

Convert reference line numbers to one-based values for display while
retaining zero-based indexing when reading the corresponding source
line.

Update the MCP marker tests accordingly.

Change-Id: I9b7675756e8b828ac7f00fbe371d7e908cfe426c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/805820
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Madeline Kalil <mkalil@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

gopls/internal/mcp/references.go

diff --git a/gopls/internal/mcp/references.go b/gopls/internal/mcp/references.go
index d49bce1..2e82a42 100644
--- a/gopls/internal/mcp/references.go
+++ b/gopls/internal/mcp/references.go
@@ -62,7 +62,7 @@
 		} else {
 			continue
 		}
-		fmt.Fprintf(&builder, "The reference is located on line %v, which has content `%s`\n", r.Range.Start.Line, lineContent)
+		fmt.Fprintf(&builder, "The reference is located on line %v, which has content `%s`\n", r.Range.Start.Line+1, lineContent)
 		builder.WriteString("\n")
 	}
 	return textResult(builder.String()), nil

gopls/internal/test/marker/testdata/mcptools/references.txt

diff --git a/gopls/internal/test/marker/testdata/mcptools/references.txt b/gopls/internal/test/marker/testdata/mcptools/references.txt
index 0172076..455e59b 100644
--- a/gopls/internal/test/marker/testdata/mcptools/references.txt
+++ b/gopls/internal/test/marker/testdata/mcptools/references.txt
@@ -38,13 +38,13 @@
 The object has 3 references. Their locations are listed below
 Reference 1
 Located in the file: $WORKDIR/a/a.go
-The reference is located on line 2, which has content `func Foo() {} //@loc(Foo, "Foo")`
+The reference is located on line 3, which has content `func Foo() {} //@loc(Foo, "Foo")`
 
 Reference 2
 Located in the file: $WORKDIR/a/a.go
-The reference is located on line 5, which has content `Foo()`
+The reference is located on line 6, which has content `Foo()`
 
 Reference 3
 Located in the file: $WORKDIR/b/b.go
-The reference is located on line 5, which has content `a.Foo()`
+The reference is located on line 6, which has content `a.Foo()`
 

gopls/internal/test/marker/testdata/mcptools/symbol_references.txt

diff --git a/gopls/internal/test/marker/testdata/mcptools/symbol_references.txt b/gopls/internal/test/marker/testdata/mcptools/symbol_references.txt
index b08a0a2..fdfc08b 100644
--- a/gopls/internal/test/marker/testdata/mcptools/symbol_references.txt
+++ b/gopls/internal/test/marker/testdata/mcptools/symbol_references.txt
@@ -40,19 +40,19 @@
 The object has 3 references. Their locations are listed below
 Reference 1
 Located in the file: $WORKDIR/a/a.go
-The reference is located on line 2, which has content `func Foo() {}`
+The reference is located on line 3, which has content `func Foo() {}`
 
 Reference 2
 Located in the file: $WORKDIR/a/a.go
-The reference is located on line 5, which has content `Foo()`
+The reference is located on line 6, which has content `Foo()`
 
 Reference 3
 Located in the file: $WORKDIR/b/b.go
-The reference is located on line 5, which has content `a.Foo()`
+The reference is located on line 6, which has content `a.Foo()`
 
 -- @aBar --
 The object has 1 references. Their locations are listed below
 Reference 1
 Located in the file: $WORKDIR/a/a.go
-The reference is located on line 10, which has content `func (T) Bar() {}`
+The reference is located on line 11, which has content `func (T) Bar() {}`