Bug 1941380 - Cap console log string substitution precision for floating point numbers. r=baku,devtools-reviewers,jdescottes.

Test cases are added to check we're handling things correctly.

Differential Revision: https://phabricator.services.mozilla.com/D236109

devtools/shared/commands/resource/tests/browser_resources_console_messages.js

@@ -293,6 +293,37 @@ function getExpectedRuntimeConsoleCalls(documentFilename) {
       level: "log",
       arguments: ["Float from number: 1.300000"],
     },
+    {
+      ...defaultProperties,
+      level: "log",
+      arguments: ["Float from number with precision: 1.00"],
+    },
+    {
+      ...defaultProperties,
+      level: "log",
+      arguments: [
+        // Even if a precision of 200 was requested, it's capped at 15
+        `Float from number with high precision: 2.${"0".repeat(15)}`,
+      ],
+    },
+    {
+      ...defaultProperties,
+      level: "log",
+      arguments: ["Integer from number: 3"],
+    },
+    {
+      ...defaultProperties,
+      level: "log",
+      arguments: ["Integer from number with precision: 04"],
+    },
+    {
+      ...defaultProperties,
+      level: "log",
+      arguments: [
+        // The precision is not capped for integers
+        `Integer from number with high precision: ${"5".padStart(200, "0")}`,
+      ],
+    },
     {
       ...defaultProperties,
       level: "log",
@@ -552,6 +583,11 @@ async function logRuntimeMessages(browser, executeInIframe) {
     console.log("Float from not a number: %f", "foo");
     console.log("Float from string: %f", "1.2");
     console.log("Float from number: %f", 1.3);
+    console.log("Float from number with precision: %.2f", 1);
+    console.log("Float from number with high precision: %.200f", 2);
+    console.log("Integer from number: %i", 3.14);
+    console.log("Integer from number with precision: %.2i", 4);
+    console.log("Integer from number with high precision: %.200i", 5);
     console.log("BigInt %d and %i", 123n, 456n);
     console.log(
       "%cmessage with %cstyle",

dom/console/Console.cpp

@@ -2046,7 +2046,7 @@ static bool ProcessArguments(JSContext* aCx, const Sequence<JS::Value>& aData,
             output.AppendFloat(v);
           } else {
             nsCString format;
-            MakeFormatString(format, integer, mantissa, 'f');
+            MakeFormatString(format, integer, std::min(mantissa, 15), 'f');
             output.AppendPrintf(format.get(), v);
           }
         }