Use textwidth and handle precision with wide characters correctly for cfmt (#71)

Author: ScottPJones

Project.toml

@@ -23,7 +23,7 @@ keywords = ["Strings", "Formatting"]
 license = "MIT"
 name = "Format"
 uuid = "1fa38f19-a742-5d3f-a2b9-30dd87b9d5f8"
-version = "1.3.4"
+version = "1.3.5"
 
 [deps]
 

src/printf.jl

@@ -234,21 +234,28 @@ end
 # strings
 function _fmt(buf, pos, spec::FmtSpec{FmtStr}, arg)
     altf, width, prec = spec.altf, spec.width, spec.prec
-    str = altf && (arg isa Symbol || arg isa AbstractString) ? repr(arg) : string(arg)
-    slen = length(str)
-    op = p = prec == -1 ? slen : min(slen, prec)
+    s = altf && (arg isa Symbol || arg isa AbstractString) ? repr(arg) : string(arg)
+    slen = textwidth(s)
+    str, slen = 0 <= prec < slen ? _truncstr(s, slen, prec) : (s, slen)
+    prepad = postpad = 0
+    pad = width - slen
+    if pad > 0
+        if spec.leftalign
+            postpad = pad
+        else
+            prepad = pad
+        end
+    end
+
     # Make sure there is enough room in buffer
-    nlen = max(width, p)
-    buflen = sizeof(buf) - pos
-    buflen < nlen && resize!(buf, nlen + pos)
-    !spec.leftalign && width > p && (pos = padn(buf, pos, width - p))
+    nlen = pos + prepad + sizeof(str) + postpad
+    nlen > sizeof(buf) && resize!(buf, nlen)
+
+    prepad == 0 || (pos = padn(buf, pos, prepad))
     for c in str
-        p == 0 && break
         pos = writechar(buf, pos, c)
-        p -= 1
     end
-    spec.leftalign && width > op && return padn(buf, pos, width - op)
-    return pos
+    return postpad == 0 ? pos : padn(buf, pos, postpad)
 end
 
 const BaseInt = Union{Int8, Int16, Int32, Int64, Int128}

test/cformat.jl

@@ -49,12 +49,18 @@ include("speedtest.jl")
     @test cfmt( "%'f", -Inf ) == "-Inf"
     @test cfmt( "%'s", 1000.0 ) == "1,000.0"
     @test cfmt( "%'s", 1234567.0 ) == "1.234567e6"
+    @test cfmt( "%'g", 1000.0 ) == "1,000"
 end
 
 @testset "Test bug introduced by stdlib/Printf rewrite" begin
     @test cfmt( "%4.2s", "a" ) == "   a"
 end
 
+@testset "Test precision with wide characters" begin
+    @test cfmt( "%10.9s", "\U1f355" ^ 6) == "  " * "\U1f355" ^ 4
+    @test cfmt( "%10.10s", "\U1f355" ^ 6) == "\U1f355" ^ 5
+end
+
 @testset "test format..." begin
     @test format( 10 ) == "10"
     @test format( 10.0 ) == "10"