From 2b4f003a6d151380783027c3fe153cbb25028340 Mon Sep 17 00:00:00 2001
From: Sakse <17059936+dalum@users.noreply.github.com>
Date: Fri, 1 Feb 2019 21:54:41 +0100
Subject: [PATCH] Make `startswith`, `endswith` work with `Regex` (#29790)

---
 base/pcre.jl  |  1 +
 base/regex.jl | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++
 test/regex.jl | 12 ++++++++++
 3 files changed, 75 insertions(+)

diff --git a/base/pcre.jl b/base/pcre.jl
index 845187f893443..7aa91076b84ad 100644
--- a/base/pcre.jl
+++ b/base/pcre.jl
@@ -37,6 +37,7 @@ const COMPILE_MASK      =
       CASELESS          |
       DOLLAR_ENDONLY    |
       DOTALL            |
+      ENDANCHORED       |
       EXTENDED          |
       FIRSTLINE         |
       MULTILINE         |
diff --git a/base/regex.jl b/base/regex.jl
index 384d6ca3dfa21..d952f1f6ba4b8 100644
--- a/base/regex.jl
+++ b/base/regex.jl
@@ -174,6 +174,68 @@ function occursin(r::Regex, s::SubString; offset::Integer=0)
                      r.match_data)
 end
 
+"""
+    startswith(s::AbstractString, prefix::Regex)
+
+Return `true` if `s` starts with the regex pattern, `prefix`.
+
+!!! note
+    `startswith` does not compile the anchoring into the regular
+    expression, but instead passes the anchoring as
+    `match_option` to PCRE. If compile time is amortized,
+    `occursin(r"^...", s)` is faster than `startswith(s, r"...")`.
+
+See also [`occursin`](@ref) and [`endswith`](@ref).
+
+# Examples
+```jldoctest
+julia> startswith("JuliaLang", r"Julia|Romeo")
+true
+```
+"""
+function startswith(s::AbstractString, r::Regex)
+    compile(r)
+    return PCRE.exec(r.regex, String(s), 0, r.match_options | PCRE.ANCHORED,
+                     r.match_data)
+end
+
+function startswith(s::SubString, r::Regex)
+    compile(r)
+    return PCRE.exec(r.regex, s, 0, r.match_options | PCRE.ANCHORED,
+                     r.match_data)
+end
+
+"""
+    endswith(s::AbstractString, suffix::Regex)
+
+Return `true` if `s` ends with the regex pattern, `suffix`.
+
+!!! note
+    `endswith` does not compile the anchoring into the regular
+    expression, but instead passes the anchoring as
+    `match_option` to PCRE. If compile time is amortized,
+    `occursin(r"...\$", s)` is faster than `endswith(s, r"...")`.
+
+See also [`occursin`](@ref) and [`startswith`](@ref).
+
+# Examples
+```jldoctest
+julia> endswith("JuliaLang", r"Lang|Roberts")
+true
+```
+"""
+function endswith(s::AbstractString, r::Regex)
+    compile(r)
+    return PCRE.exec(r.regex, String(s), 0, r.match_options | PCRE.ENDANCHORED,
+                     r.match_data)
+end
+
+function endswith(s::SubString, r::Regex)
+    compile(r)
+    return PCRE.exec(r.regex, s, 0, r.match_options | PCRE.ENDANCHORED,
+                     r.match_data)
+end
+
 """
     match(r::Regex, s::AbstractString[, idx::Integer[, addopts]])
 
diff --git a/test/regex.jl b/test/regex.jl
index 6fc5c2f159749..cb3fa965f8a50 100644
--- a/test/regex.jl
+++ b/test/regex.jl
@@ -66,6 +66,18 @@
     # Regex behaves like a scalar in broadcasting
     @test occursin.(r"Hello", ["Hello", "World"]) == [true, false]
 
+    @test startswith("abc", r"a")
+    @test endswith("abc", r"c")
+    @test !startswith("abc", r"b")
+    @test !startswith("abc", r"c")
+    @test !endswith("abc", r"a")
+    @test !endswith("abc", r"b")
+
+    @test !startswith("abc", r"A")
+    @test startswith("abc", r"A"i)
+    @test !endswith("abc", r"C")
+    @test endswith("abc", r"C"i)
+
     # Test that PCRE throws the correct kind of error
     # TODO: Uncomment this once the corresponding change has propagated to CI
     #@test_throws ErrorException Base.PCRE.info(C_NULL, Base.PCRE.INFO_NAMECOUNT, UInt32)