Merge pull request #19 from ARCJ137442/master

Detailed message for "rule unreachable" error

Author: exaexa

Project.toml

@@ -1,7 +1,7 @@
 name = "PikaParser"
 uuid = "3bbf5609-3e7b-44cd-8549-7c69f321e792"
 authors = ["The developers of PikaParser.jl"]
-version = "0.6.0"
+version = "0.6.1"
 
 [deps]
 DocStringExtensions = "ffbed154-4ef7-542d-bbb7-c09d3a79fcae"

src/grammar.jl

@@ -42,7 +42,15 @@ function make_grammar(
         end
     end
 
-    all(opened .> 0) || error("some grammar rules not reachable from starts")
+    # At this point, all rules should be opened at least once. If some grammar
+    # rules are unreachable from the starts, report them explicitly in the
+    # error message to ease the debugging.
+    if !all(opened .> 0)
+        unreachable_names = map(Base.first, rules)[opened.==0]
+        error(
+            "grammar rules not reachable from starts: $(join(repr.(unreachable_names), ", "))",
+        )
+    end
 
     reordered = rules[topo_order]
 

test/clauses.jl

@@ -90,6 +90,27 @@ end
     @test_throws DomainError P.flatten(rules, Char)
 end
 
+@testset "Unreachable rules are reported" begin
+    rules = Dict(:xxx => P.seq(:yyy, P.fail), :yyy => P.epsilon, :zzz => P.epsilon)
+
+    @test_throws ErrorException P.make_grammar([:xxx], P.flatten(rules, Char))
+    @test begin
+        # this should simply not throw anything
+        P.make_grammar([:xxx, :zzz], P.flatten(rules, Char))
+        true
+    end
+
+    @test try
+        P.make_grammar([:xxx], P.flatten(rules, Char))
+    catch e
+        b = IOBuffer()
+        showerror(b, e)
+        errorstring = String(take!(b))
+
+        (occursin(":zzz", errorstring) && all(!occursin(errorstring), [":xxx", ":yyy"]))
+    end
+end
+
 @testset "Corner-case epsilon matches" begin
     str = "whateveρ"