Intl.NumberFormat disregards maximumSignificantDigits

[jskeate]

• Version: 10.7, 10.8 (possibly others, tested these two)
• Platform: Darwin 15.6.0, Linux 4.17.10-1-ARCH

$ node
> new Intl.NumberFormat(undefined, { maximumSignificantDigits: 3 }).format(1234500)
'1,234,500'
> new Intl.NumberFormat(undefined, { maximumSignificantDigits: 3 }).format(1234560)
'1,234,560'
> new Intl.NumberFormat(undefined, { maximumSignificantDigits: 1 }).format(1234560)
'1,234,560'

Previously (node v9.2, at least), this behaved correctly:

> new Intl.NumberFormat(undefined, { maximumSignificantDigits: 3 }).format(1234500)
'1,230,000'
> new Intl.NumberFormat(undefined, { maximumSignificantDigits: 3 }).format(1234560)
'1,230,000'
> new Intl.NumberFormat(undefined, { maximumSignificantDigits: 1 }).format(1234560)
'1,000,000'

[devsnek]

@nodejs/intl @nodejs/v8

[vsemozhetbyt]

These are results with some relevant Node.js and V8 (Windows 7 x64, common Node.js builds with small-icu):

new Intl.NumberFormat(undefined, { maximumSignificantDigits: 1 }).format(1234560)

Node.js 06.14.3 V8 5.1
'1,000,000'

Node.js 08.11.3 V8 6.2
'1,000,000'

Node.js 10.8.0 V8 6.7
'1,234,560'

Node.js 11.0.0.2018-08-01.nightly V8 6.8
'1,234,560'

Node.js 11.0.0.2018-07-14.v8-canary V8 6.9
'1,000,000'

Node.js 11.0.0.2018-08-01.v8-canary V8 7.0
'1,234,560'

[srl295]

undefined

• thought 1: it shouldn't matter but it is probably better to pin this to something such as the following, to remove uncertainty

new Intl.NumberFormat(['en-US'], { maximumSignificantDigits: 1 }).format(1234560)

• thought 2: does this work in v8 (d8) directly? what is the behavior there?

[srl295]

• thought 3 - 'there oughtta be a test for this'

[devsnek]

@srl295

V8 version 6.9.0 (candidate)
d8> new Intl.NumberFormat(['en-US'], { maximumSignificantDigits: 1 }).format(1234560)
"1,000,000"

[srl295]

so right now i'm concerned about this

> new Intl.NumberFormat(['en'], { minimumSignificantDigits:1, maximumSignificantDigits: 3 }).resolvedOptions().maximumSignificantDigits
6

and 3 kinda ≠ 6

[vsemozhetbyt]

-p "new Intl.NumberFormat(['en-US'], { maximumSignificantDigits: 1 }).format(1234560)"
Node.js 06.14.3 V8 5.1
1,000,000
Node.js 08.11.3 V8 6.2
1,000,000
Node.js 10.8.0 V8 6.7
1,234,560
Node.js 11.0.0.2018-08-01.nightly V8 6.8
1,234,560
Node.js 11.0.0.2018-07-14.v8-canary V8 6.9
1,000,000
Node.js 11.0.0.2018-08-01.v8-canary V8 7.0
1,234,560

[srl295]

reading http://icu-project.org/apiref/icu4c/classicu_1_1DecimalFormat.html#sigdig

[vsemozhetbyt]

V8 version 7.0.167
d8> new Intl.NumberFormat(['en-US'], { maximumSignificantDigits: 1 }).format(1234560)
"1,000,000"

> process.versions.node
'11.0.0-v8-canary2018080644d0a70123'
> process.versions.v8
'7.0.158-node.1'
> new Intl.NumberFormat(['en-US'], { maximumSignificantDigits: 1 }).format(1234560)
'1,234,560'

[srl295]

There's an ICU bug. https://unicode-org.atlassian.net/browse/ICU-20063 // @sffc

[srl295]

v8 is broken too unless they've mitigated this.

here's a hackaround that will should work for any ICU version:

diff --git a/deps/v8/src/objects/intl-objects.cc b/deps/v8/src/objects/intl-objects.cc
index 60c3a0721b..adbb6b460e 100644
--- a/deps/v8/src/objects/intl-objects.cc
+++ b/deps/v8/src/objects/intl-objects.cc
@@ -274,20 +274,31 @@ void SetNumericSettings(Isolate* isolate, icu::DecimalFormat* number_format,
     number_format->setMaximumFractionDigits(digits);
   }
 
-  bool significant_digits_used = false;
+  int32_t mndig = -1;
+  int32_t mxdig = -1;
+  bool mndig_used = false;
+  bool mxdig_used = false;
   if (ExtractIntegerSetting(isolate, options, "minimumSignificantDigits",
-                            &digits)) {
-    number_format->setMinimumSignificantDigits(digits);
-    significant_digits_used = true;
+                            &mndig)) {
+    mndig_used = true;
   }
 
   if (ExtractIntegerSetting(isolate, options, "maximumSignificantDigits",
-                            &digits)) {
-    number_format->setMaximumSignificantDigits(digits);
-    significant_digits_used = true;
+                            &mxdig)) {
+    mxdig_used = true;
   }
 
-  number_format->setSignificantDigitsUsed(significant_digits_used);
+  // per https://unicode-org.atlassian.net/browse/ICU-20063
+  // the following call trashes the min/max settings. So call it first.
+  number_format->setSignificantDigitsUsed(mndig_used || mxdig_used);
+
+  // Now it's safe to call set min/max
+  if(mndig_used) {
+    number_format->setMinimumSignificantDigits(digits);
+  }
+  if(mxdig_used) {
+    number_format->setMaximumSignificantDigits(digits);
+  }
 
   number_format->setRoundingMode(icu::DecimalFormat::kRoundHalfUp);
 }

[srl295]

v8 does NOT have a mitigation for this that I could see… https://github.com/v8/v8/blob/master/src/objects/intl-objects.cc#L294 … so v8 is broken, depending on the ICU version used.

but :( looks like v8 put a hack into its ICU version — here is the patch

it might be better to just put this same patch into node's ICU for this specific version.