Improve help grammar for field hints (#51178)

stdlib/REPL/src/docview.jl

@@ -643,8 +643,9 @@ function fielddoc(binding::Binding, field::Symbol)
             end
         end
     end
-    fields = join(["`$f`" for f in fieldnames(resolve(binding))], ", ", ", and ")
-    fields = isempty(fields) ? "no fields" : "fields $fields"
+    fs = fieldnames(resolve(binding))
+    fields = isempty(fs) ? "no fields" : (length(fs) == 1 ? "field " : "fields ") *
+                                          join(("`$f`" for f in fs), ", ", ", and ")
     Markdown.parse("`$(resolve(binding))` has $fields.")
 end
 

stdlib/REPL/test/docview.jl

@@ -4,21 +4,17 @@ using Test
 import REPL, REPL.REPLCompletions
 import Markdown
 
-@testset "symbol completion" begin
-    @test startswith(let buf = IOBuffer()
-            Core.eval(Main, REPL.helpmode(buf, "α"))
-            String(take!(buf))
-        end, "\"α\" can be typed by \\alpha<tab>\n")
-
-    @test startswith(let buf = IOBuffer()
-            Core.eval(Main, REPL.helpmode(buf, "🐨"))
-            String(take!(buf))
-        end, "\"🐨\" can be typed by \\:koala:<tab>\n")
+function get_help_io(input)
+    buf = IOBuffer()
+    eval(REPL.helpmode(buf, input))
+    String(take!(buf))
+end
+get_help_standard(input) = string(eval(REPL.helpmode(IOBuffer(), input)))
 
-    @test startswith(let buf = IOBuffer()
-            Core.eval(Main, REPL.helpmode(buf, "ᵞ₁₂₃¹²³α"))
-            String(take!(buf))
-        end, "\"ᵞ₁₂₃¹²³α\" can be typed by \\^gamma<tab>\\_123<tab>\\^123<tab>\\alpha<tab>\n")
+@testset "symbol completion" begin
+    @test startswith(get_help_io("α"), "\"α\" can be typed by \\alpha<tab>\n")
+    @test startswith(get_help_io("🐨"), "\"🐨\" can be typed by \\:koala:<tab>\n")
+    @test startswith(get_help_io("ᵞ₁₂₃¹²³α"), "\"ᵞ₁₂₃¹²³α\" can be typed by \\^gamma<tab>\\_123<tab>\\^123<tab>\\alpha<tab>\n")
 
     # Check that all symbols with several completions have a canonical mapping (#39148)
     symbols = values(REPLCompletions.latex_symbols)
@@ -27,10 +23,7 @@ import Markdown
 end
 
 @testset "quoting in doc search" begin
-    str = let buf = IOBuffer()
-        Core.eval(Main, REPL.helpmode(buf, "mutable s"))
-        String(take!(buf))
-    end
+    str = get_help_io("mutable s")
     @test occursin("'mutable struct'", str)
     @test occursin("Couldn't find 'mutable s'", str)
 end
@@ -75,6 +68,27 @@ end
     @test REPL.summarize(b, Tuple{}) isa Markdown.MD
 end
 
+@testset "Struct field help (#51178)" begin
+    struct StructWithNoFields end
+    struct StructWithOneField
+        field1
+    end
+    struct StructWithTwoFields
+        field1
+        field2
+    end
+    struct StructWithThreeFields
+        field1
+        field2
+        field3
+    end
+
+    @test endswith(get_help_standard("StructWithNoFields.not_a_field"), "StructWithNoFields` has no fields.\n")
+    @test endswith(get_help_standard("StructWithOneField.not_a_field"), "StructWithOneField` has field `field1`.\n")
+    @test endswith(get_help_standard("StructWithTwoFields.not_a_field"), "StructWithTwoFields` has fields `field1`, and `field2`.\n")
+    @test endswith(get_help_standard("StructWithThreeFields.not_a_field"), "StructWithThreeFields` has fields `field1`, `field2`, and `field3`.\n")
+end
+
 module InternalWarningsTests
 
     module A