fix(rbac): Custom mutations fallback to FooBaseInput when FooInput isn't available

[benjie]

Fixes #373

If insert(some_column) is not granted on foo then FooInput would have no fields, and thus is not generated.

In this case, a volatile function that accepts a foo parameter will not have a type for said parameter, and so will not add the function to the schema.

The current workaround for this is to use the smart comment in the error message:

COMMENT ON FUNCTION my_func(foo) IS E'@arg0variant base';

This tells PostGraphile to use the "base" input type (like a "super-patch" that contains all columns as nullable).

This patch makes the system fall back to the base input type automatically if no normal input type is available.

[benjie]

On second thoughts; doing this could lead to unexpected changes if you later GRANT INSERT(my_col) ON foo - suddenly the function mutation will use the FooInput (one column) rather than FooBaseInput (all columns).

I think it's better to make the user opt in to this functionality; using the comment that's already generated by the error:

  graphile-build:warn Error: Could not determine type for argument 0 ('post') of function 'post_with_suffix'; you might want to use smart comments, e.g. 'COMMENT ON FUNCTION "a"."post_with_suffix"("a"."post", "pg_catalog"."text") IS E'@arg0variant base';"
  graphile-build:warn     at argTypes.map (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build-pg/node8plus/plugins/makeProcField.js:122:13)
  graphile-build:warn     at Array.map (<anonymous>)
  graphile-build:warn     at Object.map (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build-pg/node8plus/plugins/makeProcField.js:116:32)
  graphile-build:warn     at makeProcField (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build-pg/node8plus/plugins/PgMutationProceduresPlugin.js:37:24)
  graphile-build:warn     at Array.reduce (<anonymous>)
  graphile-build:warn     at reduce (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build-pg/node8plus/plugins/PgMutationProceduresPlugin.js:28:64)
  graphile-build:warn     at SchemaBuilder.hook [as applyHooks] (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build/node8plus/SchemaBuilder.js:157:20)
  graphile-build:warn     at applyHooks (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build/node8plus/makeNewBuild.js:453:40)
  graphile-build:warn     at resolveThunk (/Users/benjiegillam/Dev/graphile-build/node_modules/graphql/type/definition.js:369:40)
  graphile-build:warn     at defineFieldMap (/Users/benjiegillam/Dev/graphile-build/node_modules/graphql/type/definition.js:551:18)
  graphile-build:warn     at GraphQLObjectType.getFields (/Users/benjiegillam/Dev/graphile-build/node_modules/graphql/type/definition.js:518:27)
  graphile-build:warn     at Object.getFields (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build/node8plus/makeNewBuild.js:544:36)
  graphile-build:warn     at newWithHooks (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build/node8plus/plugins/MutationPlugin.js:29:22)
  graphile-build:warn     at SchemaBuilder.hook [as applyHooks] (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build/node8plus/SchemaBuilder.js:157:20)
  graphile-build:warn     at Object.applyHooks (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build/node8plus/makeNewBuild.js:277:27)
  graphile-build:warn     at SchemaBuilder.newWithHooks [as buildSchema] (/Users/benjiegillam/Dev/graphile-build/packages/graphile-build/node8plus/SchemaBuilder.js:205:28)
  graphile-build:warn     at buildSchema (/Users/benjiegillam/Dev/graphile-build/packages/postgraphile-core/node8plus/index.js:200:28)
  graphile-build:warn     at process._tickCallback (internal/process/next_tick.js:68:7) +0ms

[benjie]

I've settled for improving the error message.

[benjie]

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