Only show the first parse error (#344)

Parser recovery commonly results in several errors which refer to much
the same location in the broken source file and are not useful to the
user.

Currently the most useful error is the first one, so this PR trims down
error printing to only show that one.

src/parser_api.jl

@@ -17,7 +17,13 @@ end
 
 function Base.showerror(io::IO, err::ParseError)
     println(io, "ParseError:")
-    show_diagnostics(io, err.diagnostics, err.source)
+    # Only show the first parse error for now - later errors are often
+    # misleading due to the way recovery works
+    i = findfirst(is_error, err.diagnostics)
+    if isnothing(i)
+        i = lastindex(err.diagnostics)
+    end
+    show_diagnostics(io, err.diagnostics[1:i], err.source)
 end
 
 """

test/parser_api.jl

@@ -117,28 +117,56 @@ end
 
 @testset "ParseError printing" begin
     try
-        JuliaSyntax.parsestmt(JuliaSyntax.SyntaxNode, "a -- b -- c", filename="somefile.jl")
+        parsestmt(SyntaxNode, "a -- b -- c", filename="somefile.jl")
         @assert false "error should be thrown"
     catch exc
         @test exc isa JuliaSyntax.ParseError
         @test sprint(showerror, exc) == """
             ParseError:
             # Error @ somefile.jl:1:3
             a -- b -- c
-            # └┘ ── invalid operator
-            # Error @ somefile.jl:1:8
-            a -- b -- c
-            #      └┘ ── invalid operator"""
+            # └┘ ── invalid operator"""
         @test occursin("Stacktrace:\n", sprint(showerror, exc, catch_backtrace()))
         file_url = JuliaSyntax._file_url("somefile.jl")
         @test sprint(showerror, exc, context=:color=>true) == """
             ParseError:
             \e[90m# Error @ \e[0;0m\e]8;;$file_url#1:3\e\\\e[90msomefile.jl:1:3\e[0;0m\e]8;;\e\\
             a \e[48;2;120;70;70m--\e[0;0m b -- c
-            \e[90m# └┘ ── \e[0;0m\e[91minvalid operator\e[0;0m
-            \e[90m# Error @ \e[0;0m\e]8;;$file_url#1:8\e\\\e[90msomefile.jl:1:8\e[0;0m\e]8;;\e\\
-            a -- b \e[48;2;120;70;70m--\e[0;0m c
-            \e[90m#      └┘ ── \e[0;0m\e[91minvalid operator\e[0;0m"""
+            \e[90m# └┘ ── \e[0;0m\e[91minvalid operator\e[0;0m"""
+    end
+
+    try
+        # Test that warnings are printed first followed by only the first error
+        parsestmt(SyntaxNode, """
+           @(a)
+           x -- y
+           z -- y""", filename="somefile.jl")
+        @assert false "error should be thrown"
+    catch exc
+        @test exc isa JuliaSyntax.ParseError
+        @test sprint(showerror, exc) == """
+            ParseError:
+            # Warning @ somefile.jl:1:2
+            @(a)
+            #└─┘ ── parenthesizing macro names is unnecessary
+            # Error @ somefile.jl:2:1
+            @(a)
+            x
+            ╙ ── unexpected text after parsing statement"""
+    end
+
+    try
+        # Test that initial warnings are always printed
+        parsestmt(SyntaxNode, """
+           @(a)""", filename="somefile.jl")
+        @assert false "error should be thrown"
+    catch exc
+        @test exc isa JuliaSyntax.ParseError
+        @test sprint(showerror, exc) == """
+            ParseError:
+            # Warning @ somefile.jl:1:2
+            @(a)
+            #└─┘ ── parenthesizing macro names is unnecessary"""
     end
 end