fixed width plot panel, rest hanging in margins

hanging.Rmd

---
title: "Title"
header-includes:
   - \usepackage{lipsum}
output: 
  pdf_document: 
    fig_caption: yes
    fig_crop: no
    keep_tex: yes
geometry: width=5in
---

```{r setup, include=FALSE}
library(ggplot2)
library(dplyr)
library(grid)
library(knitr)
general_fig_width <- 5
```

```{r plot, fig.show=FALSE, echo=FALSE}
p <- diamonds %>%
  sample_frac(0.3) %>%
  ggplot(aes(x = carat, y = price, color = price)) + 
  geom_point() + 
  theme_grey() + 
  theme(plot.margin = unit(c(0,0,0,0), "pt"))

g <- ggplotGrob(p)

panel_id <- g$layout$l[grep('panel', g$layout$name)]
g$widths[panel_id] <- unit(general_fig_width, "in")

fig_width <- convertWidth(sum(g$widths), "in", valueOnly = TRUE)
left_width <- convertWidth(sum(g$widths[seq_len(panel_id-1)]), "in", valueOnly = TRUE)
ggsave('plot-tmp.pdf', width=fig_width, height=4)
```

\lipsum[1]

\begin{figure}[!hb]
\hspace{`r -left_width`in}\includegraphics[width=`r fig_width`in]{plot-tmp}
\end{figure}

\lipsum[2]