Intermediary name collisions result in mapping issues with 1.15.2 MCP

[DJtheRedstoner]

On 1.15.2, some classes (for example, Widget (mcp name)) aren't obfuscated in the Minecraft jar: https://github.com/FabricMC/intermediary/blob/master/mappings/1.15.2.tiny#L29870-L29885. This means that their obfuscated, intermediary and srg mappings are all the same. However, some other unobfuscated members are given srg names (thanks forge): https://github.com/MinecraftForge/MCPConfig/blob/master/versions/release/1.15.1/joined.tsrg#L57225. This creates a situation where the Map<String, String> model for intermediary to SRG breaks down. This can be observed by importing the below project and breakpointing

architectury-loom/src/main/java/net/fabricmc/loom/util/srg/MCPReader.java

Line 118 in 3019b32

map.put(methodIntermediary, officialToMCP.get(methodTokenObf));

with a condition of methodIntermediary.equals("y") then observing officialToMCP.get(methodTokenObf) each time the breakpoint is hit.

This results in an incorrect mappings file which in turn leads to a jar with incorrect member names, resulting in compilation and remapping problems.

A sample project using 1.15.2 and MCP:

// build.gradle.kts
plugins {
    id("java")
    id("dev.architectury.loom") version "1.3-SNAPSHOT"
}

group = "org.example"
version = "1.0-SNAPSHOT"

repositories {
    // mcp 1.15.1 is missing a pom, need to do this to get it to resolve. is this also an arch-loom bug?
    maven(url = "https://maven.minecraftforge.net/") {
        content {
            includeGroup("de.oceanlabs.mcp")
        }
        metadataSources {
            artifact()
        }
    }
}

dependencies {
    minecraft("com.mojang:minecraft:1.15.2")
    mappings("de.oceanlabs.mcp:mcp_snapshot:20211108-1.15.1@zip")
    forge("net.minecraftforge:forge:1.15.2-31.1.18")
}

// settings.gradle.kts
rootProject.name = "architectury-loom-mcp-fail"

pluginManagement {
    repositories {
        gradlePluginPortal()
        mavenCentral()
        maven("https://maven.fabricmc.net")
        maven("https://maven.architectury.dev/")
        maven("https://maven.minecraftforge.net")
    }
}