[skjson] NaN while parsing long decimals

When parsing numbers with long decimals, the fast-path decimal factor
may collapse to zero.  Catch this condition (and defer to the slow parse
path).

Bug: skia:8499
Change-Id: I4e364402aecdcca9558d027a55ff297170e2a195
Reviewed-on: https://skia-review.googlesource.com/c/181179
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>

src/utils/SkJSON.cpp

@@ -740,13 +740,14 @@ private:
             f = f * 10.f + (*p++ - '0'); --exp;
         }
 
-        if (is_numeric(*p)) {
-            SkASSERT(*p == '.' || *p == 'e' || *p == 'E');
-            // We either have malformed input, or an (unsupported) exponent.
+        const auto decimal_scale = pow10(exp);
+        if (is_numeric(*p) || !decimal_scale) {
+            SkASSERT((*p == '.' || *p == 'e' || *p == 'E') || !decimal_scale);
+            // Malformed input, or an (unsupported) exponent, or a collapsed decimal factor.
             return nullptr;
         }
 
-        this->pushFloat(sign * f * pow10(exp));
+        this->pushFloat(sign * f * decimal_scale);
 
         return p;
     }

tests/JSONTest.cpp

@@ -414,3 +414,43 @@ DEF_TEST(JSON_DOM_build, reporter) {
                                                             "]"
                                             "}");
 }
+
+DEF_TEST(JSON_ParseNumber, reporter) {
+    static constexpr struct {
+        const char* string;
+        SkScalar    value,
+                    tolerance;
+    } gTests[] = {
+        { "0", 0, 0 },
+        { "1", 1, 0 },
+
+        { "00000000", 0, 0 },
+        { "00000001", 1, 0 },
+
+        { "0.001", 0.001f, 0 },
+        { "1.001", 1.001f, 0 },
+
+        { "0.000001"   ,    0.000001f, 0 },
+        { "1.000001"   ,    1.000001f, 0 },
+        { "1000.000001", 1000.000001f, 0 },
+
+        { "0.0000000001"   ,    0.0000000001f, 0 },
+        { "1.0000000001"   ,    1.0000000001f, 0 },
+        { "1000.0000000001", 1000.0000000001f, 0 },
+
+        { "20.001111814444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444473",
+          20.001f, 0.001f },
+    };
+
+    for (const auto& test : gTests) {
+        const auto json = SkStringPrintf("{ \"key\": %s }", test.string);
+        const DOM dom(json.c_str(), json.size());
+        const ObjectValue* jroot = dom.root();
+
+        REPORTER_ASSERT(reporter, jroot);
+
+        const NumberValue* jnumber = (*jroot)["key"];
+        REPORTER_ASSERT(reporter, jnumber);
+        REPORTER_ASSERT(reporter, SkScalarNearlyEqual(**jnumber, test.value, test.tolerance));
+    }
+}